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SIMATIC TIWAY I Systems Manual

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1. s seen hne nara rau nura ara rana NomnalOperatlon 2 REED rias Exception Procedules ciue sebo erp RRERELRIC cie Primitive Field Definiions 0cocccccccccc nnn nura ra ran Prirmitive Field occccot todo 0 ROTEN ira ata p tt TIWAY I Primitive Code Subset ies cet et el nC c dete d ena Chapter6 TWAY I Cable Installation Overview INTOUCUON i1 rita rai as Scope of Section cia ii ic RT D CR A ZR TR ee TIVAY I Unit Loading Versus Cable Distance sseeeeennn nn n n n n n n n n n n nn TIVAY Hardware Media Components eene nnn A A Twisted Pair Cabling 25e RR ados Three Important Considerations cccccccccccccc nnne nnn nnn nn Syste m EXPANSION rocha maenad ia aai aa arya RR Re red i a deia ach ds Sytem He XD A EET Noise Contents vii 6 6 6 7 6 8 6 9 Local Line Tap Spacing cooccccoccccccc nnne nnn nn General Rules for Tap Line Installations sssssssssse ett 6 11 Cable Routing 0 cece cece eee eee nana aaa a a aai i a n a n Other Considerations eR da epe RE RR RR ERR RACER E RT Rd do RC 6 12 xeu M ida aa ia dd ls 6 12 Installing RedundantCableS oooccccccccccc nnn nnne nnn Reconlkeeping 232 3442 EGER VIXERIT AREE ARES RR AA ELE RAE RUE E Appendix A Glossary 60s cece cece cece n e A Appendix B TIVAY I Primitives B l B 2 el T Organization of this Appendix sssssssssssssssse nett nnn Applicabale Documents
2. ccoocccccccccc nennen Contents 3 12 3 13 3 14 3 15 3 16 3 17 3 18 3 19 TIVAY I Relationship to the PM550 CIM Local Line nnn n nn nnn Local Line Performance Characteristics 0 00 3 31 TIWAY Enhancements to the Local Line 0 0 eee 3 31 TIWAY Protocols de ER ELE RI bedded a eed RR ERR ite Rs 3 32 TIVAY I Conformant Compatible Products i iie n Category E scorsi rra phat a ue PEE bee ba Racing ak 3 33 Categon Rm 3 33 TAY I ConformantProducts c cece cece cece eee ssh TIWAY Compatible Products sseee nnnm Functions of the Network Primary sseeeeenm mnn nnn Message Flow Control cese RR esha ee bea DPF RA EX eg kd ge das 3 36 NetworcinitialiZation xcu oppo Rer RER E Cere REREURF PED FR Expte 3 37 Error Detection and Recovery cc cece eene ener 3 37 TIVAY I Primary Host Support Requirements enn nnm mmn Siemens 5100 Network Primary ssssssse me 3 38 TAY I Performance Example sssssn m me emen nn nnn 9 6KbpsOperatiOh 2o xx anc ben a ee e debacle d AWE ES e o ttr e ucl 3 41 115 2 Kbps Operation vere eee RR RE apes FCR edo aU eae nea 3 42 Network Planning Service NPS seen mme Level One Level Two Level Three Level Four Chapter4 Network Architecture 4 1 4 2 Introduction i ILE verear os ace Ere race ei REOR UN UE Ron E Rs EORR ORT RR Network Arc hitecture P rpos
3. 6 e Hmmm HDLC Unbalanced Link UN ssssses RR RRR HR HDLC Symmetrical LINK UA 1 0 0 ccc ccc cece mmn HDLC Balanced Link BA Combined Stations 0 0 ccc cece I HDLC Frame SUUCtUIG oai eee pe da Ri aad e e RC Oke HDLC Command Response Sequence ssssssse ens Contents ix 5 1 5 2 5 3 5 4 5 5 5 7 5 8 5 10 5 11 5 12 5 13 5 14 5 15 5 16 5 17 5 18 5 19 5 20 5 21 5 22 5 23 5 24 5 25 5 26 5 27 5 28 6 2 6 3 6 4 B 1 B 2 B 3 B 4 B 5 B 6 B 7 TIWAY VOSI Model Relationships 0ooccooccccccccccc m m TIWAY OSI Model Relationships Physical Layer 00 000 c cece eee Low Speed Modem Interface Connector Pin Assignments 00000 c cece TIWAY I OSI Model Relationships Data Link Layer 0000 c ccc ee TIWAY LHDEC Fraime emite eR ed ed oe eae PER Era ce Ace ia ZENO BIE ASS MEO I s P Um HDLC Frame Span of Zero Bit Insertion 6 eee TIWAY HDLC Frame AddressField 0000s TIWAY HDLC Frame Control Field 0 000 Control Feld Format shacicndeosercivinnerns Rice E bondage sie Barba Robur Gabe hd onan FRMR Response I Field Format 00 cece cece ttt eee Control Field Format 525 ed eR REDE RE eee eed dci a ae E eda TIWAY HDLC Frame Information Field ssssssssseee eee TIWAY VHDLC Frames FCS Field 2c encanta ease eee Rea HDLC Frame Span 0fCRC 2 isch eee kcex A CRUCE RUE le eg TIWAY I
4. Nevertheless there are many similarities between Local Area Networks and Long Haul Networks Packet communication techniques became well known after the U S Defense Department developed the long haul network called ARPANET and at the sametime the costs of computer hardware decreased sharply As the need for low cost high speed communications between a wide variety of small computing devices gave riseto Local Area Networks LAN structure and protocols grew out of the continuing evolution of long haul packet technology although LAN hardware technology came from both long haul packet networks and digital computer I O buses Traditional local computing system configurations have been clustered as shown in Figure 2 1 Such a system has frequently consisted of a minicomputer with disks printers and nonintelligent terminals attached The present trend however is toward systems with more and more powerful individual workstations which will allow many users to share common resources and which feature a high degree of interconnection between users 2 4 Introduction to Local Area Networks SIMATIC TIWAY I Systems Manual CLUSTER OTHER NETWORKS PROFESSIONAL PROFESSIONAL COMPUTER COMPUTER PERSONAL PERIPHERALS Figure 2 1 Multi User Systems Become Local Area Networks A Local Area Network can answer all these needs It can help an organization achieve lower cost and higher performance levels through the sharing of network resources
5. Relationship to the OSI Model een n nnn n n nnn Media Access Control Protocol Overview n nnnm nnns Major Data Link Protocol Mechanisms enn nnn nnn nn nnn Physical Layer ccc cece cece cece nnns reece eee ee eee aaa raa aaa EleciicalCapablllY carita er RIDE SURE SO Reo Physical Layer Interfacesto the Physical Media cc cece eee ees J aDDelstop i oed oh iex vean v exa e Craw PU ete e Epp E dcr dps waded CERE SignalEevels cocos irrestricto don ee Modern Interface sirope Data Link Media Access Control Layer 0oooocccccc nnn nnn Link Control Protocol iussssesseeese IH ha Data Link Error Detection and Recovery 00occcccoccccc ens Network Initialization isssesseee er Station Mitala ton acere e BE ae ee IN EN OLE a a dE Data Ue ALS 21 ee haa a EA EEA NIM Timing Considerations 0 e Media AccessControl Hierarchy 1 0 0 cette SUPEIVISONY SCAN iii been RR odd Ho ea ia Paes Network Layet 2 23234 dota oda ROTER RR EORR TCR CUR RC ACRI CR a OR Overview of Network Layer Protocol 6 6 cece Permanent Virtual Circ uit Initia liza tion Network Layer Initialization sarei iiiam e Transport Layer 2 ccc cece eee Session Layer wu eee aaa a a ak i a a a a i a a n n n a n n TIVAY I Presentation and Application Layers 0ccccoccc n nnn n nnn SpecialConsiderations 2 0 ccc eect e ESAS TIWAY T PritrllblVBS ontario rita aaa ad a Primitive FUN
6. e Autoboct which permits automatic reload of the operating system and application programs from the hard drive starts execution at a user defined program location e Selectable double high and double wide character display e Automatic self diagnostics during power up Hardware error messages are displayed on both screen and printer e User selectable CRT saver Automatically shuts screen down after 45 minutes at idle restarts automatically upon activity from keyboard or host SIMATIC TIWAY Systems Manual The Siemens 5100 can be programmed to alert an operator to equipment malfunctions to critical operations occurring on the plant floor or to any other situation requiring supervisory attention It can be used with all Programmable Controllers having TI WAY interfaces See Figure 3 18 COLOR ee se VIDEO A QUEE PDOS REAL TIME DISK MEMORY MATRIX PRINTER MULT TASKING UNIT OPERATING SYSTEM DEVICE DRIVER COMMUNICATIONS CONTROL CONTROL UNIT UNIT PROCESSOR Figure 3 18 Siemens 5100 as TIVAY I Primary Siemens 5100 System Components The 5100 system components are e Siemens 5110 Control Unit e Siemens 5120 Memory Unit e Siemens 5130 Color Terminal and keyboard e Siemens 820 RO Printer SIMATIC TIWAY Systems Manual TIWAY Overview 3 39 TIWAY I Primary Host Support Requirements continued Siemens 5100 System Characteristics The 5100 is a powerful system in a small package Designe
7. 32 HH 33 CC TT AAAA DDDD DDDD lt gt Repeated 33 HH SS TWATI Primitives B 31 Primitive Definition continued Remove Define Write and Gather Request Response Program Condition Request Response Poll Condition Request Response B 32 TIWAY Primitives Table B 9 Summary of Primitives c ontinued 40 AA DDDD EEEE 40 HH AAAA DDDD 41 AAAA NNNN 41 HH 42 AAAA DDDD DDDD lt gt lt gt Repeated 42 HH 50 CC TT NNNN AAAA 51 HH EEEE DDDD DDDD lt gt Repeated 52 EEEE TT AAAA DDDD DDDD lt gt lt gt Repeated 52 HH EEEE DDDD DDDD lt gt Repeated 53 CC SS TT AAAA DDDD lt gt lt gt Repeated 54 HH CC TT AAAA DDDD ucc gt lt gt Repeated SIMATIC TIWAY Systems Manual Appendix C Referenced Documents The following documents are referenced in this manual Siemens publications listed may be ordered by calling 423 461 2500 during regular working hours EST USA Reference A ISO TC97 SC16 N 537 Reference model of Open Systems I nterconnectin December 3 1980 Reference B ANSI Standard X3 66 1979 Advanced Data Communication Control Procedures Reference C EIA Standard RS 449 General purpose 37 position and 9 position interface for data terminal equipment and circuit terminating equipment employing serial binary data interchange November 1977 Reference D EIA Standa
8. O structure of the network station The device oriented half usually performs message translation functions Figure 2 3 shows the network interface device SIMATIC TIWAY I Systems Manual Introduction to Local Area Networks 2 9 LAN Elements continued CONNECTED TO THE NETWORK 1 TRANSMISSION MEDIA CONNECTED TO THE B NETWORK COMPUTING DEVICE mr Pr mo muo N E T Ww O R K H A L F Figure 2 3 Network Interface Device The network interface device is usually a small computer which removes some of the signal processing load from the station computing device on which it is installed Functional Description Thenetwork oriented half of the network interface module observes transmissions on the network determines when it may send a message of its own and provides certain transformations between the signals on the network which require some modification to be compatible with different models of computers attached to the network F or example the interconnected network computers might be manufactured by different companies and not have the same protocol characteristics The network interface device usually ensures signal compatibility Typically when the network half of the interface module receives an incoming message it transfers the message to the device half of the interface The device half of the interface usually provides a half or full duplex interface to the central processor of the stati
9. The Poll Final bit and the Receive Sequence Number perform the same functions here as they doin an Information frame Unnumbered Supervisory Frame An Unnumbered Supervisory frame is identified by the first two bits in the Control Field which are set to 1 The supervisory functions which can be executed by an Unnumbered Supervisory Frame are shown in Figure 4 15 and provide a wide range of services For a specific example of a service provided see the HDLC Command Response sequence described below Cyclic Redundancy Code n this method of error detection the data message is continuously divided by a cyclic polynomial at the transmitter The resulting remainder is appended to the message frame see Figure 4 15 as the Frame Check Sequence FCS The receiver performs the same polynomial division and then compares the resulting remainder with the transmitted FCS Any discrepancy between the remainder and the FCS indicates a bit error has occurred 4 30 Network Architecture SIMATIC TIWAY Systems Manual In TIWAY I the Cyclic Redundancy Check CRC CCITT is calculated on the address control and information fields of each message frame The CRC CCITT generator polynomial is represented by the polynomial X19 X12 4X5 1 which corresponds to a 16 bit value of 1000100000010001 The CRC detects e All single double and triple bit errors e All burst errors with an odd number of bits e All burst errors of length 16 bits or less e
10. and provided as data symbols to the receiver s Data Link layer Some management functions of the physical layer are e Modecontrol such as RS 232 C line management e Clocking and synchronization for modems etc e Fault detection SIMATIC TIWAY Systems Manual Network Architecture 413 Open Systems Interc onnection OSI Model continued NOTE TIWAY uses theinternationally accepted RS 232 C 423 standard as well as the Siemens Local Line interface Local Line is a differential current drive providing long distance transmission without modems and extremely high noise immunity Siemens provides all connectors necessary for Local Line implementation The Data Link Since Layer 1 accepts and transports streams of bits without concern for Layer Layer2 their meaning it is up to the Data Link Layer to tame the raw transmission power available on the Physical Layer This task is accomplished by breaking the data up into frames ensuring sequential frame transmission and processing acknowledgement frames sent back by the receiver Layer 2 also transforms the transmission facility at Layer 1 into a line that appears error free to the Network Layer Layer 3 NETWORK LAYER LOGICAL LINK CONTROL M INTRO DATA UNIT ASSY S DE SERE DATA UNIT PROC ADDRESS FLOW CONTROL ROUTING SEQUENCE POLLING ERROR DETECT NETWORK MANAGEMENT FUNCTION DATA LINK LAYER FRAMING MEDIA ACCESS CONTROL PREAMBLE MODE LOGICAL ENTRY FRA
11. it can help promote communication within a workgroup and it is a natural system architecture for integrated office function like electronic mail filing speech store and forward and word processing It is easy to expand and it involves low initial investment because resources are shared SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 5 2 3 2 6 Local Area Networks Within a limited area such as a single building or a small group of buildings high speed data transfer between computing devices terminals and peripherals is available at a fraction of the cost of comparable long haul service over a tariffed common carrier such as the public telephone system Local Area Networks LANs are the tools which enable this high speed communication to occur A LAN consists of one or more host Central Processing Units CPUs interconnected via a local communications mechanism with a number of peripherals and memory storage units LANs are typically distinguished by their topologies their network access methods and their routing methods Three noteworthy characteristics of LANs are e Ownership by a single organization e A reach distance of not more than a few kilometers e A high total data rate throughput Introduction to Local Area Networks SIMATIC TIWAY Systems Manual 2 4 LAN Elements Local Area Networks have a combined hardware software approach to data communications They are made up of two basic har
12. 2 K Bps MAXIMUM CABLE TYPE R 1000 FT CIFT DISTANCE BELDEN 9860 ETIN HEN OM 10 9 PF 10263 FT 124 OHM BELDEN 9271 12 2 PF 3525 FT 124 OHM Figure 6 2 Maximum Cable Distance Versus Cable Type SIMATIC TIWAY Systems Manual TIWAY Cable Installation Overview 6 5 6 4 TIWAY I Hardware Media Components The media hardware components of a TIWAY network consist of the following e Siemens T Taps e Customer supplied twisted pair cabling NOTE The TIWAY network is designed for shielded twisted pair cable with a nominal characteristic impedance of 124 ohms Use of any other cable impedance will reduce network performance Flaps The Siemens custom designed T Tap is shown in Figure 6 3 below This tap is manufactured by Siemens specifically for the TI WAY Local Area Network In a typical installation the tap can be firmly mounted to the building Its design is such that it not only provides a precision engineered method for tapping into a twisted pair but also contains termination resistors is moisture proof and provides both strain relief and noise isolation for attached cabling TIWAY PRIMARY AAA TERMINATING RESISTOR TERMINATING RESISTOR INSTALLED NOT INSTALLED NOT INSTALLED INSTALLED SELECTED NOT SELECTED NOT SELECTED SELECTED Figure 6 3 Flap 66 TIWAY Cable Installation Overview SIMATIC TIWAY Systems Manual Twisted Pair Siemens recommends Belden 9860 twisted pair cabling or its equivalent for Cabli
13. 2 Manual Organization sese enne nhanh Chapter 2 Introduction to Local Area Networks cee sees Chapter3 TIWAY I Overview ssssssssse eem Chapter4 Network Architecture ssssssssseeeeee eese Chapter5 TIWAY Network Operation ssssssssseseeer Chapter6 TIWAY Cable Installation Overview 60 00 SIMATIC TIWAY Systems Manual Overview 1 1 1 1 Introduction This manual contains the information necessary to understand the Siemens Local Area Network SIMATIC TIWAY I It provides the reader with all of the following information e Thehistorical development of Local Area Networks LANs e A description of the hardware elements of LANs e LAN topologies and other LAN characteristics e A history of the development of worldwide LAN standards including the organizations involved and some defacto standards e A detailed functional description of the 7 layer Open Systems Interconnection OSI Model e High Level Data Link Control HDLC fields and functions e A detailed description of TI WAY e TheTIWAY network architecture e TIWAY installation 1 2 Overview SIMATIC TIWAY I Systems Manual 1 2 Manual Organization Section 2 Introduction to Local Area Networks Chapter3 TIMAY I Overview Chapter4 Network Architecture Chapter 5 TIVAY I Network Operation Chapter 6 TIVAY I Cable Installation Overview SIMATIC TIWAY Systems Manual
14. 99 997 of all 17 bit error bursts e 99 998 of all 18 bit and longer error bursts SIMATIC TIWAY Systems Manual Network Architecture 431 4 7 HDLC Command Response Sequence Unbalanced Mode Figure 4 16 shows a simple example of an HDLC unbalanced configuration with one Primary and one Secondary Time is plotted down the page and each arrow across the page represents a single HDLC frame moving between stations SECONDARY Bie STATION SNRM POLL BIT 1 UA FINAL BIT 1 1 NS 0 N R 0 I NS 1 N R O NS 0 N R 2 I N S 2 N R 2 FINAL BIT 1 1 NS 2 N R 1 i N S 3 N R 1 POLL BIT 1 4 FINAL BIT 1 DISC POLL BIT 1 UA FINAL BIT 1 Figure 4 16 HDLC Command Response Sequence 4 32 Network Architecture SIMATIC TIWAY I Systems Manual Function of the Primary Atthe beginning of the process the Primary wishes to send data to the Secondary so it sends an Unnumbered Supervisory F rame instructing the Secondary to Set Normal Response M ode SNRM If the Secondary is not on line it will not respond and the Primary will time out and try again later However the secondary will normally acknowledge the SNRM with an Unnumbered Acknowledge UA frame with the Final bit set returning media access back to the Primary The SNRM reset all the station variables so the next expected receive and the next send are O The Primary will now start with message O and count u
15. A two way alternate transfer of a single N protocol data unit in each direction of an N 1 connecti on N Transaction time The period between the time when an N entity requests an N transaction at an N 1 service access point and the time when the returned N protocol data unit is available at the N 1 service access point Transformation An algorithm which converts between two images Transmission line A physical means of connecting two or more locations to each other for purpose of transmitting and receiving data Transmission medium The technology coaxial cable fiber optics etc used in a given transmission line Transmitter Any station which is sending signals over a data highway Transport Layer Layer 4 of the OSI architecture Thetransport service relieves its users from any concern with the detailed way in which reliable and cost effectivetransfer of data is achieved Transport functions allow the Network Layer to be composed of more than one communication resource in tandem e g a public packet switched network used in tandem with a circuit switched network Two way alternate communication Data communication in which N protocol data units are transferred in both directions at the same time Two way simultaneous communication Data communication in which N protocol data units are transferred in both directions one direction at a time Unbalanced configuration An HDLC or ADCCP configuration involvi
16. Field PP ThePrimitive CodeField is eight bits in length The assignment of the Primitives is given in Section 4 Descriptor Field The Descriptor Field consists of different field types to define data element types location of a data element type also called address number of locations to access and current status of the attached device The Descriptor Field can contain a single descriptor or multiple descriptors as defined by the Primitives in Section 4 Attached Device Status HH Thecurrent status of the attached device when the Primitive is executed is returned with most Primitives as defined in Section 4 The format of this field is defined in the operational status component symbol of the Status Primitive Code 04 in Section 4 The attached device Descriptor Field shall be denoted HH in this Appendix Data Element Types TT The definition of the different data types to be accessed is given in Table B 2 The length of the data element type Descriptor Field is eight bits A descriptor of this type shall be denoted TT in this Appendix Table B 2 Data Element Type Descriptor Field Definition TT Data Element Type Fo 9 Instruction Execution Ladder L ogic L Variable Constant Discrete Input X Discrete Output Y Control Register CR Discrete Input Packed X Discrete Output Packed Y Control Register Packed CR Work Input WX or 7M T Word Output WY Discrete Force N e SIMATIC TIWA
17. M is theMore data bit used to control a logical sequence of data packets A data packet sequence consists of consecutive data packets where at least one data packet in the sequence has the M bit set to 1 Thelast data packet in the sequence has the M bit set to 0 Only maximum length data packets havethe M bit set to 1 NOTE TIWAY Secondaries do not support More data bit procedures Q is the data qualifier bit bit O in byte O This bit allows two levels of data over the same PVC This bit will always be set to 0 The sequence numbering of packets is performed in modulus 8 as it is done in theHDLC DataLink layer protocol The P R valueis the packet receive sequence number and the P S valueis the packet send sequence number Error Recovery An error exists at the Network Layer when the send variable does not match the expected receive variable at a network station service point or is outside of the maximum allowed window size Error recovery will consist of sending a reset request packet resetting the send and receive variables and waiting for a reset confirmation or reset request packet Flow control will start at the next data packet that was unacknowledged TheNetwork Controller Data Link service layer resetting will automatically reset and re initialize the network service layer for the entire network If the data link service layer in a secondary resets it will reset the network service layer in the secondary At this point th
18. Mode Places the secondary in the normal response mode Response to this command is UA The send receive variables are set to zero upon acceptance of this command In this mode the secondary cannot transmit until a command frame with the P bit set to one is received C U X NOTE If the PM550 CIM has a pending frame for transmission it will not discard thel frame but retains it for later transmission The send and recei ve variables are deared The only way to dear this condition is to read any pending frames SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 17 Data Link Media Access Control Layer continued DISC Disconnect Command Used to inform secondaries that the primary is suspending operation with the addressed secondary The secondary is placed in the disconnect mode and is limited to accepting a mode setting command Response to this command is UA C U DM Disconnected M ode response Response to any non mode command when the secondary is in the disconnected DI SC mode R U UI Unnumbered I nformation An I nformation command or response is provided to allow transmission of link layer data such as status broadcast or download information without impacting the N S or N R numbering at either station There is no specified secondary response required to the UI command C R U I UP Used to solicit response frames from a secondary or group of secondaries The mechanism employed to control the re
19. N 1 connection PROWAY A data highway for process control proposed by IEC TC65 SC65A Quarantine unit One or more session service data units which are only meaningful when all of them are available SIMATIC TIWAY Systems Manual Glossary A 7 Realization The specific hardware firmware and software elements that comprise a unit cf Implementation Reassembling A function in data communication of an N entity to get one N service data unit out of the multiple N protocol data units the reverse function of segmenting Recombining A function of an N entity to identify one N connection which is supported by more than one N 1 connections the reverse function of splitting Recovery procedure n data communication a process whereby a specified data station attempts to resolve conflicting or erroneous conditions arising the transfer of data Recovery unit A data unit defined and managed by the presentation entities It is nested within a commitment unit and specified for the purpose of recovery roll back when data integrity service requires Redundancy check An automatic or programmed check based on the systematic insertion of components or fields used especially for checking purposes Reset A function which permits correspondent N entities to come back to a predefined state with a possible loss or duplication of data Residual error rate undetected error rate The ratio of the number of bits incorrectl
20. OrderManual Number PPX TIWAY 8101 Refer to this history in all correspondence and or discussion about this manual Event Date Description Original Issue 06 84 Original Issue 2704941 0001 Second Edition 10 95 Second Edition 2704941 0002 LIST OF EFFECTIVE PAGES Pages Cover Copyright History Effective Pages iii xi 1 1 1 3 2 1 2 27 3 1 3 43 4 1 4 33 5 1 5 57 6 1 6 15 A 1 A 11 B 1 B 32 C 1 Registration Description Second Second Second Second Second Second Second Second Second Second Second Second Second Pages Description Contents Chapter1 Overview 1 1 12 InBodUctUoln icc aid Manual Organization s esee nnns Section 2 Introduction to Local Area Networks Chapter3 TIWAY Overview isssssssssssssss see enn Chapter4 Network Architecture ssssssssssssse nnn Chapter5 TIWAY Network Operation oooooccccccccc eee Chapter 6 TIWAY Cable Installation Overview Chapter2 Introduction to Local Area Networks 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 2 10 2 11 2 12 Introduction iii A waa ce XO RR ER c Rn 2 2 P rpose of SECTION sii cse Erb aco be aee st ore o ees A Ia td 2 2 Scope of Section io coz waste t A ORG RC n URSUS Lae ee Do EA 2 2 Classification of Networks by Size 2 nnns 2 3 Local Area Networks Long Haul Networks 0 ccseeeeeeee eee eee eee n n n n n n n n nn Simil
21. Rd ea a eat a TIWAY System Block Diagram Transmission Media ssssssssseeereeeee IWAYIModem Types sssssse eee A ORE Rad paca CR n e OS Reference Model 2 d aate A dp ey Rua e PR EP at e TIWAY I OSI Model Relationships sssssssse ee Actual Information Flow Diagram sssssssseeeee ee eas Bus Topology 2 optet blot UN AAA A A Ec Raed TIWAY I Local Line Multidrop Bus Configuration 0 cece eee TIWAY Multidrop Bus Configuration with Redundant Media ssssese TIWAY Multidrop BusConfiguration saesae serseri aa p aiaa a aa ee TIWAY I Modem Multidrop Configuration With Redundancy ssssssssseeees TIWAY I Network Polling Sequence sssssses en Siemens 5100 as TIWAY I Primary iess irice issii iato iaai danona AE A AAE E Communications Standards Organizations cc cece cts OS Model Standard Vendor Implementations 0 0c cece Open Systems Interconnection OSI Model ccc ccc cee cece eet ne OSI Model Frame Construction and Reduction 0 cee ccc eee OS Model Physcal Layer oiea iiaii iiaa a bier aa e eed e aay henge OSLModel Data Link Layer d Rei A Gd Run ERR RPG RUE RE OJ Model Network Layer sssssssssss eee OS Model Transport Eayer Casia cede deri bec ez doa eed voee ede bd deae OSI Model Session Layer ssssssssees m OSI Model Presentation Layer sssssssssssseeeee eese ees OS Model Application Layer
22. Single Poll Technique soria ae cece cece II mn TIWAY I Circular Poll Technique seiis aiai HH TIWAY l OSI Model Network Layer ci cette e The X25 Packet 1 4 cued testa a de Rd d dace ae ees Format of the Request Reset Packet sssssseseee een Format of the Reset Confirmation Packet ccc cece eee Format of the Receive Not Ready Packet ccc cece ccc ttt ees Format of the Receive Ready Packet ccc cece ett enn Format of Network Layer Data Packet Header suunas cece eect o TIWAY I OSI Model Relationships Layers6 and 7 0 cece eee Basic Primitive Struc ture ics iets hacked RPG REG aeg dash epic coe ean ws Binary Weight of the Field Sissi miiirn ei tet me Primitive Fields and Their Binary Weights sssssseeeeee TIWAY Unit Loading Versus Cable Distance and Data Rate cc cece eee oo Maximum Cable Distance Versus Cable Type 6 0 Ip T Network Cable Tap Configuration Examples ssssssssseeese ne Basic Primitive Structure eiris simini iaeaea e a nett enn Binary Weight of The FieldS 0 I nnn DEP Location FOME 3 poderoso Xeon ift a de ad eke s booa ade d oed Definition of Packed Discrete IR Data Type ssssssssss rr Definition of Loop Status Data Element uususueesssssssss nee Floating Point NUMBER eret eee e eed dae iade eR aee t aes Floating Point Examples erro De ende ee eR wi UR ae eh a
23. TIWAY Local Line constructed of shielded twisted pair cable has four major components e Atrunkline spine which can be up to 25 000 feet long e Droplines which can be up to 100 feet long e Connectors T taps e Terminators 3 14 TIWAY Overview SIMATIC TIWAY Systems Manual Connectivity Asmany as 254 stations can be linked together on a single TIWAY trunkline although at distances above 10 000 feet some compromises must be made regarding baud rates and or the number of stations Thetwisted pair cable is customer supplied and wire sizes can vary Line connectors which have pin sizes suitable for 22 to 26 AWG wire are supplied by Siemens Cable with controlled performance characteristics such as but not limited to Belden 9860 and Belden 9271 are recommended by Siemens in order to achieve high network performance Performance considerations in cable selection include distance data rate and noise immunity Terminators Signals transmitted on a twisted pair sometimes reflect at the ends of an unterminated cable and interfere with other signals on the line In TIWAY I 2 5 watt line terminating resistors located in cable blocks taps along the line act as a load to dissipate signals and minimize signal reflections The cable blocks also provide a means of connecting cable drops tothe main trunkline Media Redundancy TIWAY interface modules are especially designed to accommodate transmission media redundancy as discuss
24. TRUNK 254 SECONDARIE lt DROP CABLES gt SECONDARY SECONDARY SECONDARY SECONDARY Figure 3 12 Bus Topology TIWAY I Bus In TIWAY I the bus is a passive medium with each connecting station Characteristics listening for a message No routing decisions are required by any Secondary on the network The Primary station controls who transmits and when Each Secondary has a specific address stored in the Primary s memory When the Primary transmits the message flows away to the ends of the bus and each Secondary examines it Only the Secondary to whom it is addressed accepts it and transmits a response A Secondary on TIWAY must respond to a message from the Primary within a specific time frame A response from a Secondary flows away from the Secondary to the ends of the Bus but is accepted only by the Primary 3 22 TIWAY Overview SIMATIC TIWAY Systems Manual Any Secondary on the network can fail without disrupting the rest of the network because it fails in a manner representing a high impedence nontransmission state to the bus Since each Secondary on the bus in TI WAY has its own intelligence and can continue to operate without constant prompting by the network Primary experience has shown that this topology can be made soreliable that the possibility of catastrophic failure on the factory floor can essentially be ignored in a real world installation Bus Configurations The physical configurations of
25. The gather primitive allows reading of data from specific blocks defined by a mask The data acquisition primitives are non retentive in the event of a power loss or entering the logically disconnected state in the device addressed Any initialization or reinitialization procedures must use the data acquisition define primitive to establish simple data acquisition Define Primitive Code 50 The define Primitive specifies up to 32 random blocks of data element types E ach block can be a maximum of 128 words The blocks are referenced by number ranging from 1 to 20 hex Only the maximum number of blocks defined by one define Primitive is allowed per device Some specific devices may support only 16 random blocks and is indicated as such by the response A block once defined can be redefined to a different data element type and location by simply specifying that block number and providing the required information for a new block A block can be defined to the initial state of undefined by specifying the number of words in the block to zero Request 50 CC TT NNNN AAAA CC TT NNNN AAAA lt amp a al a gt Repeated where CC is the number assigned to that block Allowable range is 1 to 20 hex Response 50 HH SIMATIC TIWAY Systems Manual TIWATI Primitives B 23 Primitive Definition continued Gather Primitive Code 51 Thegather Primitive specifies which blocks defined by the define Primitive will be read the b
26. assuming responsibility for the organization of data flow and for the overall control of the link The controlling or responsible station is referred to as the Primary or Network Controller and the frames it transmits are called commands The other stations in the link are referred to as the secondary stations and the frames they transmit are called responses TIWAY Data Link Frame Structure Information flows between Primary and Secondary on TIWAY inside HDLC frames See Figure 5 5 The destination of the frame is specified by the address field the nature of the frame by the control field and any data specified by the control field For a general discussion of an HDLC frame and a definition of these fields see Chapter 4 of this manual The TI WAY commands and responses are encapsulated inside HDLC frames according to the following format BIT 0 8 16 24 ADDRESS CONTROL INFORMATION FCS Figure 5 5 TIWAY I HDLC Frame Flag Fields Theflagfields are HDLC message delimiters that consist of one zero followed by six ones and ending with a zero 7E hex No other bit streams on the communication link can havethis pattern This requires that the sender and the receiver perform bit stuffing and bit removal on any bit streams of five consecutive bits of ones Zero Bit Insertion The objective of zero bit insertion is to achieve complete transmission transparency of the TI WAY bit stream while maintaining the flag as a unique sequen
27. at the Network Layer Intra networking and I nter networking Intra networking Many networks consist of a collection of point to point data links with intermediate nodes through which a message must be routed on the way to its destination Such routing is performed at the network layer of each node For example an incoming frame from the data link layer is examined here to determine if the packet should be routed out a different data link to another node or whether the receiving station is a termination point and the frame needs to be routed to a higher layer within the receiving station itself A key element in intra network routing is that the network protocol is common over the network Communication oriented Sublayer The primary duties if the communication oriented sublayer of the intra networking function are e Packet assembly and disassembly e Theestablishment of calls between stations preparatory to actual message transmission e Segmentation e Blocking Packets are the units of information exchanged in Layer 3 This layer accepts data from the higher layers and converts them into packets by appending the correct headers The headers contain routing information which is determined at the beginning of a conversation between stations The establishment of calls at this layer is analogous to the establishment of calls on a public telephone Numbers can be obtained from tables in memory listing network addresses or the
28. bits Such a number divided into the bit stream at the transmitter always gives a remainder unique to the bit stream upon which the operation is performed This remainder is then appended to the data stream as the Frame Check Sequence FCS SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 23 Data Link Media Access Control Layer continued The bits which are divided by the polynomial are shown in Figure 5 15 They include the Address Control Length Information and FCS fields The FCS remainder will be unique as long as thetotal number of bits in the dividend is less than 32 767 Thereceiver performs the sametype of polynomial division on all incoming data At the completion of the message the receiver should come up with a remainder which it compares to the number carried in the FCS field of the HDLC frame Any discrepancy between the FCS and the receiver s remainder indicates that a bit error has occurred Frame Check Sequence Performance Characteristics Typical communication lines yield one bit error in 10 tothe sixth power By using the Frame Check Sequence with the 16 bit CRC error rates of one bit in 10 tothe tenth power can be achieved Further the 16 bit CRC e Detects all single double and triple errors e Detects all burst errors with an odd number of bits e Detects all burst errors of length sixteen or less e Detects 99 997 of burst errors of a length of seventeen e Detects 99 998 of burst errors on a
29. connector used by most asynchronous terminals ThelEEE is an international professional society which contributes to ANSI and also issues standards of its own The membership is composed of dues paying individuals and whileit is a U S organization its membership is international Network Architecture 4 5 Communications Standards Organizations continued Architectures Examples of Layered Architecture Two examples of layered architectures encountered in everyday activities arethe postal service and the telephone system Table 4 1 Architectures Postal Service Telephone System Layer 4 Dialogue Letter s Contents Conversati on Layer 3 Language Written Language Spoken Language Layer 2 Carrier Envelope P aper Dialing Speaking Layer 1 Media Postal Truck Communications Systems like the postal service and the public telephone network are layered somewhat as shown in Table 4 1 Each layer provides a needed service to the layer above it Furthermore each layer has its own unique protocol or set of conventions which enable it to function Protocol Examples Therouting of a letter from one address to another within the U S postal system is made possible by adherence to an orderly system of codes which control routing Those codes are zip codes street names and house numbers and in a broad sense they can be thought of as protocols since the procedures they govern are standard at both the origin and destination of a
30. contained in this data type and the definition of the contents is dependent on the spedific device type being accessed Variable The variable data type length is 16 bits Contents of this field is a 16 bit hex number in which the interpretation is application dependent B 6 TIWAY Primitives SIMATIC TIWAY I Systems Manual Constant The constant data type length is 16 bits Contents of this field is a 16 bit hex number in which theinterpretation is application dependent Discrete Input The discrete input data type length is 8 bits Contents of this field is defined in Table B 3 Discrete Output The discrete output data type length is 8 bits Contents of this field is defined in Table B 3 Control Register The control register data type length is 8 bits Contents of this field is defined in Table B 3 Table B 3 Definition of Discrete IR Data Type Data Units SIMATIC TIWAY Systems Manual TWATI Primitives B 7 Introduction continued Discrete Input Packed Thediscrete input packed data type length is 8 bits The number of locations to access descriptor field defines the number of IR bits to be packed into one or more packed discrete input data units Contents of this field is defined in Figure B 4 Discrete Output Packed Thediscrete output data packed type length is 8 bits The number of locations to access descriptor field defines the number of IR bits to be packed into one or more packed discrete output data units cont
31. data circuit Data integrity The ability of a communication system to deliver data from its origin to its destination with an acceptable residual error rate Data Link layer Layer 2 of the OSI architecture It provides functional and procedural means to establish maintain and release data link connections among network entities A data link connection is built upon one or several physical connections The objective of this layer is to detect and possibly correct errors which may occur in the physical layer In addition the Data Link Layer conveys to the Network Layer the capability to request assembly of data circuits within the physical layer i e the capability of performing control of circuit switching Data Network The means of transmitting messages between a data source and one or more data sinks A data network may contain one or more data highways interconnecting the same or different sets of devices A data network consists of these highways and the Network Layers of the stations interconnected by these highways Data signalling rate The rate expressed in bits per second at which data is transmitted or received by data terminal equi pment Data Station The set of functional units that consists of a data terminal equipment DTE data circuit terminating equipment DCE and their common interface Also called a station Data terminal equipment DTE All parts of a data station except the DCE Data transmission line A medi
32. data network by means of message switching SIMATIC TIWAY I Systems Manual Glossary A 5 Message switching The process of routing messages by receiving storing and forwarding complete messages within a data network Modem A physical entity typically part of a DCE which encodes an information signal onto or off of an analog carrier signal by varying its amplitude frequency or phase and decodes the information signal from the analog carrier by sensing this variation Multiplexing A function within the N layer by which one N 1 connection is used to support more than one N connection N Generic designator of a layer in the OSI architecture Layer numbering and the corresponding names are 7 Application 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link Control 1 Physical Network Layer Layer 3 of the OSI architecture It provides to the transport entities independence from routing and switching considerations associated with the establishment and operation of a given network connection This includes the case where several transmission resources are used in tandem or in parallel It makes invisibleto transport entities how the Network Layer uses underlying resources such as data link connections to provide network connections Open System A system which can be interconnected to others according to established standards Open System Interconnection OSI architecture A model of system archit
33. dosing flag of a message ever contains six 1 bits in a row 1Raw0111111111001111110111111110 data 2 Bit stuffed 0 1 1 1 1 101111001111101011 11101110 data Stuffed Bits SIMATIC TIWAY Systems Manual Network Architecture 425 High Level Data Link Control HDLC continued Modes of HDLC defines two primary modes of operation Operation e Normal Response Mode NRM In this mode the network Secondary must receive explicit permission from the Primary to transmit NRM is used in TI WAY I e Asynchronous Response M ode ARM or ABM In this mode any station on the network can transmit point to point whenever it wants ARM is supported only in point to point configurations but is not supported in TI WAY I HDLC Station HDLC defines three primary types of station configurations Configurations Unbalanced Link UN Theunbalanced link is the configuration used in TIWAY I In it the network Primary is responsible for overall flow control and error control on the data link See Figure 4 12 Characteristics are e OnePrimary e Multiple Secondaries e Usually referred to as a multidrop line e Uses NRM operation SECONDARY A SECONDARY B Commands gt PRIMARY il Responses SECONDARY C SECONDARY D Figure 4 12 HDLC Unbalanced Link UN 4 26 Network Architec ture SIMATIC TIWAY I Systems Manual NOTE TIWAY uses the unbalanced normal response mode UNRM si
34. dropline length are considered as a double drop from the dosest tap SIMATIC TIWAY Systems Manual TIWAY Cable Installation Overview 611 6 7 Cable Routing Cable routing should be planned as if the path between all stations on the on the network were free of obstructions after which all three dimensional aspects of the installation should be considered The next step is to modify the first routing to account for obstructions then calculate the amount of cable needed NOTE All local and national electrical and fire codes should be observed when installing this network Other Aside from physical obstructions such as posts walls partitions and the Considerations like electrical interference should also be avoided Some sources of such interference are e Power distribution mains switching mains The main lineis not a problem e Arcing motors e Welders e General EMR sources Routing In general there are three routes network cabling may take e Under flooring e n ceiling e Inside surface ducting Any combination of these three routes may be used on a single network The choice is often determined by whether the building or buildings in which the network is being installed already exists or is under construction In under floor routing the cable can be enclosed within ducts or in the case of raised flooring in the open air Duct enclosed underfloor systems are usually expensive and while they are b
35. ice tee REGE RE REE Head Rha ded bhi ded geek ede d e Signal Leve lS zi srpen ma dx ERR De AEN Pea UR ERU eRe eiu Ede Re au Modern Interface setae etos dados i dh due An aide e bd dde Sade ad de ded Contents 5 6 57 5 8 5 9 5 10 5 11 5 12 6 1 6 2 6 3 6 4 6 5 Data Link Media Access Control Layer cccccccccccccc n nn n n n n n nnn nnn Link Control Protocol ss sirit eee eee Data Link Error Detection and Recovery ssici isda ioaea aokii eese Network Initialization si seris icira e aii Hmmm Station InitializatiOn iciatis trece Aa ecce cec Ferca dich cic ce Cc bEN NEITUIae TIE NIM Timing Considerations ssssssseeeee A O RA Media Acces Control Hierarchy ssssssssssssseeeeee eee Supervisory SC ali eus br hte ER tace C AAA AAA ee e OR Ge e hate er ls WEA Network Layet cia a TR CERE ROO ROCA CEU VOR UR AA se Overview of Network Layer Protocol 2 0 0 nnns Permanent Virtual Circuit Initialization ssssssssseeeen m Network Layer lnitializatioNn oooooccooccccrrrrr m A Hmm Transport Layer ccoccccccoc hn nhanh aes Session Layer wie eee aaa a a aa a a i a a n i a n n n a n n TIVAY Presentation and Application Layers seen n nnn nnn Special Considerations Tasc Codes ceca a RA dorem eric xac eic ee a d ded TIAS EPI IBIVO S dain adap da reo Ace rae od ene wv fend eR e do a UE d eai C a Primitive FUNC TONS oz acc CE eR OR ci Basic Procedure Rules
36. in a layer A sublayer can be bypassed in the establishment of phase as well as in the data phase a sublayer uses entities and connections of its layer Switched Virtual Circuit SVC Also called Virtual Call A Network facility providing a temporary association between two network connecti on endpoints initiated by a call request to the Network layer as specified in CCITT Recommendation X 25 Switchover A change from using one data path or data circuit to using another Normally used in the context of fault tolerance where the switchover is made to utilize a redundant path or circuit SIMATIC TIWAY I Systems Manual Glossary A 9 Synchronous transmission A mode of data transmission such that the time of occurrence of each signal representing a bit is related to a fixed time frame System A set of one or more programmable devices with associated software peripherals terminals human operators physical processes information transfer means etc that forms an autonomous whole capable of information processing System management appli cati on process An application process which executes system management functions ultimately responsible for controlling and supervising open systems Time division multiplex A means of supporting more than one link connection on a single data circuit by enabling data transmission by each station intermittently generally at a regular intervals and by means of an automatic distribution N Transaction
37. in the yellow band H gt P Spare Set to zero Method Of Expansion The method of expansion will take one or both of two forms The first is the extension of the basic structure formats when the need is to extend the addressing range or other fields beyond sixteen bits The second is the expansion of the Primitive set or data type set beyond the number of unique codes eight bits can provide SIMATIC TIWAY I Systems Manual TWATI Primitives B 11 Introduction continued B 12 TIWAY Primitives Structure Formats The most significant bit of the Primitive Field being set shall indicate the Primitive is in the extended structure format In this format the following fields are redefined to have the indicated lengths The Primitive definitions and assignments in Section 4 remain unchanged except for the indicated field lengths Data Element Location Thelength of the data element location descriptor shall be thirty two bits Field Expansion The primitive and the data element type Descriptor Fields shall have an extended length when the field contains all ones Note that the most significant bit of the Primitive Field is the extended structure indicator The extended field shall be the next eight bits following the field indicating expansion For example the Primitive Field containing 7F will indicate that the following next eight bits contain the Primitive definition A Primitive Field containing FF will indicate that the following n
38. letter Another orderly system semantic in nature is language itself While the traditional definition of protocol does not make it synonymous with language a language is nevertheless a connected orderly method of transferring meaning and therefore data between entities The contents of a letter for example make sense to a reader because of an agreement between a writer and a reader about the meaning of marks on paper and the arrangement of those marks into words and sentences Such marks must of course be understandable to all users In languages dissimilar protocols like F rench and English requiretranslation This is alsotrue of dissimilar network protocols In the postal service architecture shown in Table 4 1 Layer 3 language provides a service with which everyone is familiar to the next higher layer the person using it in dialogue Note that language as a layer has no interest in the meaning of the dialogue itself The language merely provides a servicetothe higher level by enabling manual recording of the writer s thoughts The contents Layer 4 of the letter can thus be said to be transparent to the language Layer 3 4 6 Network Architecture SIMATIC TIWAY Systems Manual Computer Architectures System Operation Each Layer of the postal service architecture provides a serviceto all the higher levels The use of dialogue and language in a letter is of little value for example unless some means of trans
39. maximum of 32 PCs e TM990 Secondaries on a Local Line have a maximum address capacity of 63 but have a maximum of only 32 active stations at any given time e Local Line throughput is limited to 9 6 Kbps and below TMWAY I TIWAY enhancements to the Local Line are Enhancements to the Local Line e Connectivity provided for 520 530 5TI and PM 550 controllers e increase by a factor of 8 the number of addressable stations from 32 to 254 e Increase by a factor of 12 the physical throughput from 9 6 Kbps to 115 2 K bps e Better error detection through the inclusion of an information Length Field in the HDLC frame data field e Higher system availability through redundancy both on the transmission media and the Network Interface Devices e Theimplementation of device independent high level Primitive Task Codes which enable the network primary to converse with all computing devices on the network in the same language e Increased geographical coverage up to 10 000 feet with 254 stations up to 25 000 feet with premium cable and fewer stations e Modem interface up to 19 2 Kbps asynchronous RS 232 C limit up to 115 Kbps synchronous using a clock signal from modem e Architecture conforms to the industry standard OSI 7 layer model SIMATIC TIWAY Systems Manual TIWAY Overview 3 31 TIWAY Relationship to the PM550 CIM Local Line continued TIVAY I Protocols TIWAY Data Link Layer Layer 2 protocol and
40. not responded previously Any stations found in the DISC state shall be issued an SNRM command and upon a UA response logged into the station active log unless higher level services have requested that a station be put in the DI SC mode The Supervisory Scan will always be performed The active station log is accessible to higher level services SIMATIC TIWAY Systems Manual TIWAY Network Operation 527 Data Link Media Access Control Layer continued TIWAY I Single Poll Technique The polling technique in which the TIWAY network primary requests data from a particular secondary and does not proceed to a second secondary until the first response has come back is called the Single Poll Technique This technique is illustrated in Figure 5 16 PRIMARY SECONDARY XMIT I FRAME TO SEC 1 RESPONSE DELAY SETUP DELAY XMIT RR TO SEC 1 RESPONSE DELAY RNR SEC NOT DONE SETUP DELAY XMIT RR TO SEC 1 RESPONSE DELAY RECEIVE FRAME FROM SEC 1 XMIT FRAME TO SEC 2 RESPONSE DELAY SETUP DELAY XMIT RR TO SEC 2 RESPONSE DELAY RECEIVE FRAME FROM SEC 2 Figure 5 16 TIWAY I Single Poll Technique 5 28 TIWAY Network Operation SIMATIC TIWAY Systems Manual For the Primary to request information from a particular Secondary in TIWAY I it must first transmit an frame to the Secondary In the case which is illustrated in Figure 5 16 Secondary 1 is polled with an frame In the Sec
41. performing its specified function tothe total time that function is scheduled to be performed Bit error rate The ratio measured at the physical interface between the number of errors received in a bit stream and the number of bits originally transmitted Bit rate See Data Signalling Rate Block A series of characters considered as a unit for error and sequence checki ng purposes SIMATIC TIWAY Systems Manual Glossary A 1 Blocking A function of an N entity to map multiple N service data units on one N protocol data unit Bridge A data station providing a Network layer relay function Broadcast or group message A message addressed to two or more but not necessarily all stations on a data highway Busy state A state in which an entity is unavailable for communication because of internal activity Byte An assembly of several bits usually eight in number Call Clearing Release of a network connection conforming to the X 25 packet level protocol for Switched Virtual Circuits Call Establishment Establishment of a network connection conforming to the X 25 packet level protocol for Switched Virtual Circuits Centralized connection A type of multi endpoint connection in which data sent by the entity associated with the central connection endpoint is received by all other entities Data sent by one of the other entities is only received by the central entity Character A group of bits usually between 5 and 8
42. point and is his entry into the network Because of this the content of the application layer is up to the user himself There are primarily three types of application users e An operator e An application program such as a data base containing sales figures inventory information etc e A peripheral device such as a printer a terminal or a programmable controller NOTE It is here that TI WAY has implemented a protocol service known as Primitives Primitives offer many benefits to industrial LAN users and are rapidly growing in industry acceptance Congratulations on your choice of TIWAY and Siemens programmable controllers Application Services TheApplication Services are itemized in Figure 4 11 and are self explanatory APPLICATION PERIPHERAL OPERATOR PROGRAM DEVICE END USER APPLICATION SERVICES NETWORK DATA UNIT ASSY ME MAPPING bey PROC oe AUTHENTICATION 1 MANAGEMENT AUTHORIZATION ERROR DETECT FUNCTION END USER AVAILABILITY CO OUNTING DIALOG DISCIPLINE DATA SYNTAX ERROR RECOVERY RESP Figure 4 11 OSI Model Application Layer 4 24 Network Arc hitecture SIMATIC TIWAY I Systems Manual 4 5 High Level Data Link Control HDLC HDLC Overview Protocol Features Bit Stuffing As previously noted Siemens TI WAY Local Area Network uses the Data Link Layer protocol known as HDLC Because of its importance to network integrity a more detailed explanation is p
43. reach the N entity which serves the corresponding N service access point N Service data unit An amount of N interface data whose identity is preserved over the N connection Session synonym for session connection A cooperative relationship between two application entities characterizing the communication of data between them Session dialogue service A session service controlling data exchange delimiting and synchronizing data operations between two presentation entities Session layer Layer 5 of the OSI architecture Its purpose is to provide the means for cooperating presentation entities to organize and synchronize their dialogue and manage their data exchange Signal level The rms voltage measured during an RF signal peak usually expressed in microvolts referred to an impedence of 75 ohms or in dBmV the value in decibels with respect to a reference level of 0 dBmV which is 1 millivolt across 75 ohms N 1 Si mplex transmission N 1 data transmission of N 1 service data units in one preassigned direction only Slave station A station that is selected by a master station to receive data and or respond with data Station Synonym for data station Station address Synonym for data link connection endpoint identifier Store and forward mode A manner of operating a data network in which packets or messages are stored before transmission to the ultimate destination Sublayer A grouping of functions
44. remainder of this section requires an understanding of the internal operating parameters of all computing devices attached to any given TIWAY network Some examples of the kinds of knowledge required are an understanding of programmable controller e Ladder memory which is used to store the ladder logic portion of a user s program e Variable or V memory which is used to store and manipulate numbers e Timer Counter and drum storage used to store the preset and dynamic values for timer counter and drum instructions e Status words which contain the online monitored status of internal functions such as battery low current CPU scan time etc e mage Registers which provide storage for the current status of each discrete X input Y output C control relay Word WX input or WY output in the PC e Characteristics such as CPU memory size CPU controlled I O loops task codes diagnostics program execution processes and the like Of particular importance for a good understanding of the Primitives defined in the following paragraphs is a grasp of the methods by which a programmer or other specialist communicates with a PC in a language coherent to that PC For this reason a brief discussion of Task Codes is provided here Ordinarily instructions sent to a single PC from a host or controlling device such as a Video Programming Unit VPU are called commands Answers returned to a host from the PC are called
45. responses At their most basic level these commands take the form of serial bit streams sent out over the communications media between the computers These bit streams must conform to certain conventions in order to be understood by the computing devices involved Commands issued to the PM 550 and the Series 500 Programmable Controllers are Task Codes A Task Code usually consists of a two digit hexadecimal number embedded in a character oriented message format F or example the Series 500 Task Code instructing a Programmable Controller to switch from Program Mode to Run Mode is the hexadecimal number 32 SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 47 TIWAY I Presentation and Application Layers continued Thetotal number and complexity of Task Codes varies for any given PC However in any instance where the TI WAY network includes computing devices such as the PM550 CIM which are not fully TI WAY conformant the network controller Primary software will be required to communicate with these computing devices using Task Codes or functional commands rather than the Primitives described here n other words conformant TI WAY devices as defined in Chapter 3 use the Primitives to convey data and instructions Compatible devices as defined in Chapter 3 may communicate using Task Codes TIVAY Primitives Primitives are high level commands that allow a user to access data types in all different secondaries in
46. second computer and thetask in which it has an interest In establishing a session the user must provide the remote address of the computer with which he wants to converse Session addresses are intended for use by users or their programs whereas transport addresses are intended for use by transport stations See Figure 4 9 4 20 Network Architecture SIMATIC TIWAY Systems Manual PRESENTATION LAYER QUARANTINE QUENE SESSION MANAGEMENT IMITIATIONITERMIN bd SPEAKER RULES A UNIT PR MANAGEMENT ae CHAINING ane SESSION FUNCTION SEQUENCE ee ERROR DETECT LAYER SYNCHRONIATION CHECKPOINTING TRANSPORT LAYER Figure 4 9 OSI Model Session Layer A session might be also be used for example to log into a remote time sharing system or transfer a file between two computers Other functions at the Session Layer are e Theinitiation of the session e Thetermination of the session e Establishing which station has speaker rights e Chaining e Bracketing e Quiescing e Synchronizing e Checkpointing SIMATIC TIWAY I Systems Manual Network Architecture 421 Open Systems Inter onnection OSI Model continued Presentation Layer Chaining An example of chaining If a printer is page oriented and the Transport Layer connection can only accept lines a chain is started by breaking a page into lines The lines are transmitted to the receiving computer with an indicator of the end of the chain marking the e
47. secondary is manually switched to a mode that will disconnect it from a primary Under these conditions the Network Controller will log that a secondary is disconnected and will reestablish the information transfer state ITS Error Recovery A Secondary station that has accumulated a specified number of consecuti ve checkpoint errors shall be issued a DISC command and logged out of the active station log which is maintained in the network Primary Higher level services in the Primary and the Secondary shall be notified of this action The Secondary station that is disconnected must wait until the next Supervisory Scan poll cycle for disconnected stations to respond with a DM and havethe primary issue an SNRM command Higher level services must monitor the performance of all secondary stations and instruct the Data Link services to permanently log out a troublesome station A primary that receives power loss a fatal error condition or a restart reset command will perform Network Initialization upon removal of the fault condition A secondary that receives a power loss fatal error condition or a restart reset command shall initialize its Data Link variables enter the LDS state and wait for the primary to poll the Secondary station SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 25 Data Link Media Access Control Layer continued Network Initialization Station Initialization Data Transfer NIM Timing Considerati
48. shielded twisted pair cable is simply two wires twisted together to form a single line It is inexpensive readily available and easy to use Depending on the original drive method chosen it can offer high performance for minimum cost Baseband Coaxial Cable A coaxial cable is more expensive than shield twisted pair cable but offers the advantage of less data loss at very high transmission rates Fiber Optic Fiber optic transmission is a relatively new technology Electrical signals are translated to light pulses by a modulator and transmitted as light signals over a fiber cable At the end of their route the light signals are detected by the receiving node and reconverted to electric signals by photoelectric diodes The light source can bea light emitting diode LED or laser diode Laser diodes provide the highest signal throughput While fiber optic provides excellent electrical isolation with low error rates current receiver transmitter technology limits its practical applications in industrial networks Network Interface Network interface hardware is the hardware which connects all the Hardware separate computing devices on the network to the network communications media and enables the devices to interact with each other A network interface module may be viewed as having two parts a network oriented part that performs transmission control functions as required on the network media and a device oriented part that fits into the
49. short bursts and much time can be wasted routing each burst Packet switching on the other hand divides whole messages into packets and transmits each along with its source and destination address The route is established as the packet travels Each packet is assigned a flow control sequence number so that any individual packet of a message that may arrive out order can be assembled at the receiving node Packet switching is a very efficient method of data transmission and is the method chosen for TIWAY I SIMATIC TIWAY Systems Manual Introduction to LocalArea Networks 2 19 28 LAN Reliability Enor Detection Redundancy LAN reliability requirements are extremely high Users often require and designers usually provide reliability in excess of 99 996 This means that not only the combined hardware software components must be near perfect but that any LAN installation possess a high degree of redundancy A corollary to reliability is the capacity to diagnose and respond to failures on the network Error detection in transmitted messages and redundant hardware are the two principle methods by which LAN designers insure virtually error free operation The purpose of error detection is to insurethat a transmitted message arrives unchanged at a receiver This means that a receiver must be able to recognize inaccuracies in incoming bit streams and correct for them There aretwo fundamental methods for doing this error correcting method
50. structure shown in Figure B 1 The binary weight associated with the definition of the fields used in the Appendix is shown in Figure B 2 The minimum field length is 8 bits with a minimum field increment of 8 bits This will allow for octet testing of data links frames at the data link media access control layer The maximum length of Descriptor and Data Unit fields is 270 bytes for TI WAY network interface modules attached to programmable controllers The 270 bytes exdude the Primitive Code and protocol control fields Other devices connected to TI WAY will support frame lengths in excess of 270 bytes The actual length supported is dependant on device type and must be ascertained with the primitive format configuration primitive Each of the basic field types shown in Figure B 1 is described in the following sections LENGTH PRIMITIVE DESCRIPTOR FIELDS s DATA UNIT FIELD s MAY BE REPEATED Figure B 1 Basic Primitive Structure FIRST BIT TRANSMITTED LEAST SIGNIFICANT BIT MOST SIGNIFICANT BIT Figure B 2 Binary Weight of The Fields SIMATIC TIWAY Systems Manual TIWATI Primitives B 3 Introduction continued B 4 TIWAY Primitives Length Field LLLL TheLength Field is sixteen bits in length The Length Field contains the number of octets in the Primitive which includes the Primitive Code Field Descriptor Field s and Data Unit Field s A Length Field containing a zero has no Primitive fields Primitive Code
51. the packet header The session control word value 20007 is the same for input and output data packets TI WAY will not support session control or task IDs The session control word value is not interpreted but it must be included in input and output data packets to ensure proper operation of the Primary station software LEAST SIGNIFICANT BIT 0 7 BIT POSITION X 25 LOGICAL CHANNEL NUMBER PACKET HEADER s D o9 CONTROL DESTINATION ID DESTINATION ID ENCODED ASK DESTINATION ID DESTINATION ID Mos FOR RECEIVER SOURCE ID SOURCE ID AND SENDER SOURCE ID SOURCE ID USER DATA Q DATA QUALIFIER BIT ALWAYS SET TO O Figure 5 24 Format of Network Layer Data Packet Header SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 41 Network Layer continued The destination and source I Ds follow the session control word They are binary coded decimals assigned at network generation by the Network Controller Data packets arriving at a Secondary station are referred to as arriving at the destination ID In data packets sent from the secondary station the same ID is referred to as the source ID The IDs are included in every data packet entering and leaving the secondaries ThelDs are used by theNetwork Controller internally to identify different data link service points with the same data link addresses on different physical links They can also be used by the Network Controller to identify different internal tasks
52. time and decrease cycle time Plant operations can be monitored constantly and trouble spots can be identified before they become real problems Programs can be developed that assemble production and process data and store it at single point for use in process analysis and resulting optimization decisions SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 23 2 12 Unique Features 2 24 A LAN has several unique features that are not found within traditional communication networks The high transmission speed and low error rates are almost the inverse of classical communications The ability to interconnect different devices over the same medium offers several advantages One LAN cable may be used to attach many devices This can simplify cable installation costs since the network can be shared by many different users or user groups Most LANs arerelatively low in cost for their performance The network is a one time cost and there are no monthly line costs as with public networks Most LANs also provide a method to broadcast packets to all broadcast nodes or a select set multicast of nodes on the network This feature can be used to simplify many network problems Introduction to Local Area Networks SIMATIC TIWAY I Systems Manual 2 13 LAN Advantages As noted a number of user benefits can be realized using local area networks These benefits are summarized as follows e Modular growth path e Access t
53. to a primary with FRMR or CM DR Command Reject when the primary elicits a retransmission Subsets of Commands and Responses TIWAY supports the following subsets of commands and responses for the dass of procedures defined as U nbalanced Normal Response Mode See Table 5 1 TIWAY I Network Operation SIMATIC TIWAY Systems Manual Table 5 1 TIWAY Command Response Subsets Primary Station Secondary Station Command Response Command Response Transmission Reception Reception Transmission Not supported by PM550 CiM Encoding of Command Response Fields TheNumbered and Unnumbered commands responses formatted in Figure 5 12 havethe following values in the bit fields indicated See Table 5 2 The encoding is most significant bit to least significant bit Table 5 2 Encoding of Command Response Field SIMATIC TIWAY Systems Manual TIWAY Network Operation 521 Data Link Media Access Control Layer continued 5 22 BIT POSITION INFORMATION e NUMBERED SUPERVISORY FIRST BIT TRANSMITTED LEAST SIGNIFICANT BIT Figure 5 12 Control Field Format Information Field Thelnformation Field contains the message of higher level services to corresponding stations The X 25 packet header may be contained in the message body depending on the higher level services selected The higher level Primitive will be contained here or in the case of the PM550 CIM the Task Code See Reference
54. 01 On Unforced 81 On Forced F Renove Fare Not all device types support force Used in write primitives only Table B 5 Definition of Word Force Data Type Data Units Value Hex Data Unit Definition 00 DDDD Unforced Word Value 01 DDDD On Word Value FF Remove F orce Not all device types support force Used in write primitives only Timer or Counter Preset Thetimer or counter preset data type length is 16 bits Contents of this field is a 16 bit hex number Timer or Counter Current Thetimer or counter current data type length is 16 bits Contents of this field is a 16 bit hex number Drum Step Preset The drum step preset data type length is 8 bits Contents of this field is restricted to the number of steps a drum instruction type has defined in a specific device type Drum Step Current Thedrum step current data type length is 8 bits Contents of this field is restricted to the number of steps a drum instruction type has defined in a specific device type SIMATIC TIWAY Systems Manual TIWAT Primitives B 9 Introduction continued B 10 TIWAY Primitives Drum Count Preset The drum count preset data type length is 16 bits Contents of this field is defined by the drum instruction type defined in a specific device type Loop Gain Theloop gain data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Reset Theloo
55. 15 eerie kae di Sick Parr ne EXER E t RC iced se p Primitive Definition 0occccccccc hh aa nara ra kara nara nana Primitive Assignment Rules is sasapi iie aea a aa i ener Exception and Status Primitive Codes COMO ME m EE Data Acquisition Primitive Codes seseerirerreri ereden is ep EE E e Basic Procedure Rules 23 34 eaaa a di nice baad erac e Floaating Point Representation 6 ccc ene Primitive SUMMA ze ERE te knee ape RO ERR Eae Ed ear re Caci Appendix C Referenced Documents 00s0ceeeeeeeeeeeeeeeeees Cl viii Contents List of Figures 2 1 2 2 2 3 2 4 2 5 2 6 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 3 10 3 11 3 12 3 13 3 14 3 15 3 16 3 17 3 18 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 4 10 4 11 4 12 4 13 4 14 4 15 4 16 Multi User Systems Become Local Area NetWorkS 00 cece eee eee en Hardware Elements of a Typical Local Area Network cece cece eee eae Network Interface Device 20 ccc cece hh Bus Topology m xac tbc ice te eae dee d i Au ack M ge Atle eat dae et Re A The Ring Topology sic iiec teen Rte b EM CERE Rey ee PIG CEDE e E qo du ees The Star Topology scene khpEERRESORIR ERREUR e ae TIWAY I System Block Diagram sssssssssseeeeeeeee eem ee TIWAY System Block Diagram NCM ssssssseeene eem ms TIWAY System Block Diagram NIM ssssssseeen e eae Block Diagramot NIM es cte exte ERR naa RR TR
56. 26 SUMMAI arice narar IILIIUILIILDILIDCILLITUUTIT 2 27 SIMATIC TIWAY I Systems Manual Introduction to Local Area Networks 2 1 2 1 Introduction Purpose of Section Scope of Section Until the early 1970s a company could purchase communications facilities for less money than it could buy additional computing power This led tothe growth of centralized computing centers connected to remote input output devices such as printers and terminals H owever the rapid development of microprocessors reversed that Today the cost of a small computer makes it very economical to process data close to its source and then transmit summaries back to a control center rather than to purchase and operate a mainframe computer to do all the processing This has led tothe development of computer networks which are defined as the interconnecting of computing devices so that they can communicate with each other The purpose of this section is to introduce and define Local Area Networks LANs This section will discuss the general characteristics of LANs Topics covered are e Classification of networks by size e Elements and characteristics of LANs e Transmission media characteristics e LAN topology and media control e LAN media access methods e LAN interface hardware characteristics e LAN software e Reliability error detection and redundancy e Gateways e LAN applications e LAN standards 2 2 Introduction to Local Area Networks SIMATIC
57. AY conforms to the OSI standard in most major respects OSI MODEL TIWAY 3 27 7 APPLICATION COMMUNICATION PRIMITIVES PRESENTATION SESSION MANAGER REDUNDANT TRANSPORT MEDIA SELECTION SESSION MULTI TASK MEN X 25 PVC a LOCAL Figure 3 10 TIVAY I OSI Model Relationships 3 20 TIWAY Overview SIMATIC TIWAY Systems Manual Summary Figure 3 11 shows how a typical transmitted data block is built as it passes from one level to another prior to transmission across the physical connection The data or message generated by the primary resident task is processed at each level Headers are added to each level as required for identification and control and the combined result is passed to the Data Link line control level OUTGOING FRAME INCOMING FRAME CONSTRUCTION REDUCTION END A C i APPLICATION APPLICATION PRESENTATION PRESENTATION session L sssw i TRANSPORT o O DATA UNIT COMMUNICATIONS PATH PHYSICAL TRANSMISSION MEDIA Figure 3 11 Actual Information How Diagram SIMATIC TIWAY Systems Manual TIWAY Overview 3 21 3 9 TIWAY I Topology Network topology is the pattern of interconnection used among various stations on the network TI WAY topology is the Bus Multi access channel illustrated in Figure 3 12 or a Star configuration which is logically identical tothe bus described NETWORK PRIMARY BUS MAIN
58. CUONS 2i aae ire E dee Oe Ede A de e CER e adn Basic Procedure RuleS 0 oocccccocccccc nennen eee eee Normal Operation ssec RRIC DERI ROG HERE DEA RR ROO Oa KE doing Exception Procedutes 22 eee bed ee aee E CERRO ARR Primitive Field Definitions 0oooococococ e Imm Primitive Fle lg 2 cobra oa o CORR c on eR Wa E pr ba pha CR kee Ed eo Rc TIWAY Primitive Code Subset sssssee RR IR SIMATIC TIWAY I Systems Manual TIWAY Network Operation 5 1 5 1 Introduction As discussed in Chapter 3 TI WAY is designed to provide multidrop communications services for all Siemens Energy amp Automation products over a common transmission media This transmission media may consist of industrial Local Line LL constructed of twisted pair cable as described in Chapter 3 or other customer selected media utilizing customer supplied modems The TI WAY local line will provide multidrop communications for as many as 254 stations at distances up to 10 000 feet Geographic coverage for systems with customer supplied modems is dependent on the characteristics of the modems In general TI WAY interfaces will operate compatibly with systems currently employing the Local Line with existing PM 550 Computer Interface Modules CI M s and the 990 308 Industrial Communication Modules TI WAY interfaces are described in Chapter 3 and consist of the network controller cards and network interface modules which are defined as TIWAY
59. DD where Symbol Value Diagnostic Definition DD 00 Diagnostics passed 01 Attached device diagnostic tests failed 02 Network module diagnostic tests failed 03 Network module and attached device diagnostic tests failed Read Read Block Primitive Code 20 Read block will access contiguous data element locations from a given data element location Request 20 TT NNNN AAAA Response 20 HH DDDD DDDD lt gt lt gt Repeated where DDDD is defined by data element type being accessed Read Random Primitive Code 21 Read random will access data element locations that may or may not be contiguous Each data location accessed is specified Request 21 TT AAAA TT AAAA oa gt lt gt Repeated Response 21 HH DDDD DDDD lt gt Repeated where DDDD is defined by data element type being accessed and returned in the same order in which they were requested SIMATIC TIWAY Systems Manual TIWAT Primitives B 19 Primitive Definition continued Write Write Block Primitive Code 30 Write block will replace contiguous data element locations from a given data element location with the data specified in the Request Request 30 TT AAAA DDDD DDDD gt lt gt Repeated where DDDD is defined by data element type being accessed Response 30 HH Write Random Primitive Code 31 Write random will replace data element locations that may or may not be contiguous with the d
60. F SecCtIOfr metes doit Tace bre edu Saada ai peia re eee o dde ed 2 2 Classification of Networks by Size ooccooccccccccccc 2 3 Local Area Networks Long Haul Networks 00cceeeeeeee eee nnn n n n n n n n n n n nn Similarities of LANs to Long Haul Networks sssusa aena 2 4 Traditional Local Communications SysteMsS 0 0 ees 2 4 Local Area Networks ccc cece eee cece e eens cece ar rr LAN Elements 00sec cece eee eee eee eee a ra a aa a an n n n The Hardware Elements 0 ccc cece cect menn Transmission Media 2 2 0 eee m Network Interface Hardware The LAN Software Element 0 00 cece cece me Network Topology and Media Conttol ccccceeeeeeeeeee eee nnn n n n n n n n n n n nnn 2 12 Bus lopology rivero rre REE MENU ERA 2 13 Message ThrO0UYGApUt occcccocccccccc nra rr rn n n n Message Routing ssssssssssssnuununnnnnnnnnnnsnnsnusnusuunnunnnnnnnnnnnno A A o endo ue ub Ens Eno Detecti M c 2 20 Redundangc ya sui ae ci rs te Ce ele et e A A de E E at 2 20 LAN Applications sssssssssssssuunusnnnnnnnnnnnnnsnusnusuunnunnnnnnnunnnno 2 23 Resource Shartllig seccion ide Y rope ae 2 23 Unique Features ccccocccccccc nnns nna raa ra rn n nn LAN AdvamtageS ccoocccccocccc nana aaa aa aa aa aa a aa n a n n n n n 2 25 LAN Standards isissssssssses sse aa aaa aar aia a ri n n Additional Information cc Ree RR RE ER E ER ER ER TERR 2
61. I Layer3 sssssssssssssse teas Transport Layer OS Layer4 secisisiiciana ii teens The SESSION Layer x ness id Satie de edie e a Bree a etna PY wen EA Presentation La Ver isse ba niet ee a Rieke Ade dle det ote ce e e dente arated A Application Layer uci cepe pads hie es ahaa e FR eda RT ac CR cedo dea he High Level Data Link Control HDLC cece ccc eee eee eee n nnn nn nn ADEC ONGIVIGW i dus scena era does cae Ere ied ues Ad ed ene du Roca he OA RO Rs Protocol Fea tU cio ce edad e EIER e a ewe die E e t Rs Bit SUMING p EEUU Modesof Operation ues ere eem eedem dock eI I Rd REOR aca bcd ied ead HDLC Station Configurations HDLC Frame Structure on cece csc c eee aaa ra ar ra aaa Hag Fields eer REF Rete obese Ws Me e ER e IU edo ce t AddressField scraps Control Field eese rte oett e D nac e RT ona E Ri e a e COR TR Frame Check Sequence FCS Field HDLC Command Response Sequence Unbalanced Mode IntiodUc On i uso ci caia CR 8 73 8 ERER RE CR 4 ORT RR EA sept is Terminology seis Ex kee hit Aen Pa eae A Sea epo aie aoe TIVAY I Relationship to the OSI Model een n nnn n n nn Media Access Control Protocol Overview een n n n n n n n n n nn Major Data Link Protocol Mechanisms nnn nnn n nnn nnn nn Physicallayer sis ccc ee recaps dee eee eed ee ElectncalCompatibiliby 1 eee Dia keri i e exer a dd Rd Physical Layer Interfacesto the Physical Media suusa Jabberstop jas c
62. ITIONING OF ALL COM MUNICATION FUNCTIONS INTO A UNIVERSAL FRAMEWORK OF SERVICES AND PROTOCOLS PROVIDE COMMON BASIS FOR COOR DINATION OF STANDARDS DEFINITION DEVELOPMENT AND VALIDATION PROMOTE FLEXIBILITY I E LAYER IM PLEMENTATION SELECTED TO MATCH APPLICATION AVAILABLE TRANSMIS SION MEDIA AND DESIRED SERVICES PROMOTE UNIVERSAL CONNECTIVITY STARTED IN 1977 MEMBER NATION APPROVAL EXPECTED 1983 Figure 4 3 Open Systems Interconnection OSI Model SIMATIC TIWAY Systems Manual Network Architecture Open Systems Inter onnection OSI Model continued OSI Model Functions Layers and Services The function of the OSI Model shown in Figure 4 3 is to partition all network communication functions into a universal framework of services and protocols By doing so it provides a common basis for the coordination of standards definition development and validation Networks using the OSI Model or variations of it are open to other networks using the same standard While the number name and function of each network layer may differ from application to application the purpose of each layer in all networks is to offer specific services to the next higher layer At the same time each higher layer is shielded from the details of how the lower layer services are actually implemented This approach is designed to promote both flexibility and universal connectivity In the OSI Model each system is composed of a
63. IWAY unit loading versus cable distance and data rate e TIWAY hardware components e Threeinitial planning considerations e Tapspadng e Cable routing e Record keeping SIMATIC TIWAY Systems Manual TIWAY Cable Installation Overview 63 6 3 TIWAY I Unit Loading Versus Cable Distance Figure 6 1 illustrates the relationship of cable distance to unit loading and data rate for two types of twisted pair cable Notethat the cable distance in thousands of feet is shown vertically the maximum number of units that may be attached is shown horizontally 19 2 K bps DM OR LOWER 38 4 K bps l O lt 57 6 K bps S 115 K bps o 2 n o e o ul o z T o e ul Q Oo n 50 CABLE UNIT LOADING NUMBER OF STATIONS Figure 6 1 TIWAY I Unit Loading Versus Cable Distance and Data Rate 6 4 TIWAY Cable Installation Overview SIMATIC TIWAY Systems Manual As shown in Figure 6 1 up to 75 stations using Belden 9860 cable or its equivalent can be attached to a network operating at 38 K bps and having a spine length of 20 000 feet At 115 2 Kbps the maximum length of a TI WAY Local Area Network having 254 stations is 10 000 feet Figure 6 2 shows a formula for empirical calculations at various data rates for different cable manufacturers based on cable parameters FORMULA DISTANCE 1000s OF FEET V 1800 X RESISTANCE 1000 FT X CAPACITANCE FT X DATA RATE EXAMPLES AT 115
64. M in Appendix C or Reference K in Appendix C depending on the secondary station The X 25 Packet Header is explained beginning in Section 5 7 and the TI WAY Primitives are defined and explained beginning in Section 5 10 of this manual 0 8 16 24 ADDRESS CONTROL INFORMATION Figure 5 13 TIWAY I HDLC Frame Information Field TIWAY I Network Operation SIMATIC TIWAY Systems Manual Frame Check Sequence n factory environments the control of a production process is critical which means that the data flowing on the network must be error free To achieve the necessary signal reliability the TIWAY Frame Check Sequence uses the CCITT 16 bit Cydic Redundancy Check CRC as specified in Chapter 12 of Reference B in Appendix C The CRC is calculated on the address control and information fields excluding the 0 bits inserted during the HDLC bit stuffing procedure Refer to Figure 5 14 and Figure 5 15 0 8 16 24 FLAG ADDRESS CONTROL INFORMATION Figure 5 14 TIWAY I HDLC Frame FCS Field BIT 0 8 16 24 FLAG ADDRESS CONTROL INFORMATION FLAG SPAN OF CRC Figure 5 15 HDLC Frame Span of CRC CRC Cyclic Redundancy Check The CRC employed in TIWAY isa method for checking all the data transmitted by any computing device on the network by continuously dividing the data stream by a cyclical polynomial An example of a 16 bit polynomial is a 16 bit word with all bits set to zero except the 16th 12th 5th and 1st
65. ME PROCESS DELIMITERS TRAFFIC MONITOR ROUTING CONTROL RIGHT TO XMIT ERROR DETECT SRCIDEST ADDR CONTENTION RESOLUTION FCS ERROR RECOVERY PHYSICAL LAYER Figure 4 6 OS Model Data Link Layer 4 14 Network Arc hitecture SIMATIC TIWAY I Systems Manual Data Link Layer Block Diagram n Figure 4 6 an outgoing message travels down the left path of the figure and an incoming message travels up the right Typical questions answered here are When does a message start and when does it end Arethere any errors in the message When can this station transmit Thetwo major subdivisions of the Data Link Layer are e TheLogical Link Control Sublayer e TheMedia Access Control Sublayer Logical Link Control Sublayer This sublayer is responsible for overall mode control of the data link Station connect disconnect normal response etc are established here Within this sublayer there is a logical link service access point address which provides some routing within the data link Flow control is accomplished using message sequence numbers Media Access Control Functions of the Media Access Control sublayer are e Delimits the frame e Defines the type of frame e Adds the actual source and destination of the physical address e Adds an Error Check Sequence e Controls when a station may transmit on the media e Acts asa media traffic monitor to determine which traffic belongs to it e Performs contention resolut
66. OSI Model HDLC e HDLC Command Response Sequence 4 2 Network Arc hitecture SIMATIC TIWAY I Systems Manual Teminology Many features used here may be unfamiliar to someone not fully conversant in data communications n some cases the definition of a new term is provided within the text but in cases where that would interrupt the flow of the information being presented the unfamiliar term should be found in the Glossary at the end of the manual It is assumed that the reader is familiar with basic computer networking theory and this manual makes no attempt to provide a comprehensive overview of that subject The assumption is also made that the reader has read and understands the material covered in Chapters 2 and 3 SIMATIC TIWAY Systems Manual Network Architecture 4 3 4 2 Communications Standards Organizations Many organizations around the world are trying to establish standards for telephone telegraph and data communication interfaces Their work encompasses the architecture of computer networks Sincethere are many different approaches to standards and many different organizations throughout the world working on them some familiarity with those organizations will be helpful in gaining an overview of the current state of the art Some of the organizations involved are listed in Figure 4 1 with a brief discussion of each organization and its approach to network architectures following Organization and Membership geog
67. Overview MOOG TON 33 duced d GER edd ka EG da e KO aaa Saeed sexe ERA WE KEY Ead CES TMAY I System Characteristics ierieueesesseseeeenn nennen enhn TAY I System Components 00 ccc cece cece nennen Network Control Module NCM The TIWAY I Primary nnn nnn nnn Non Siemens Computer Interface Module The TIWAY Adapter Network Interface Module NIM sssssssn n nnn Tansmission awe TIVAY asa Hosted Network issssssssee nennen nnns TIMAY I Topology sseeeeeeeen n Inna nna naar aa n rr nnn Baseband Signalling sese NEA PP m TIVAY Relationship to the PM550 CIM Local line eee nn TAY Conformant Compatible Products seeenennn n n n n nnn TMAY I Conformant Products euseueruessesee enne nnne nnn TMAY I Compatible Products ccccce cece ee ee eee ene eeen nnne nnn nnn Functions of the Network Primary sssssrrrssrrrrnnrrrnnrrrnunrrnnnrrrunnni TIWAY I Primary Host Support Requirements enn nmm TIVAY I Performance Example enn 3 41 Network Planning Service NPS 00cccoccccc nmm SIMATIC TIWAY Systems Manual TIWAY Overview 31 3 1 Introduction Scope of Section Teminology 3 2 TIWAY Overview This chapter provides an overview of Siemens TIWAY Local Area Network Each of the system components is introduced and discussed and network perfo
68. Primitive Definition continued Control B 18 TIWAY Primitives Change State Primitive Code 10 The change state Primitive Code will allow certain operational states to be entered Specific operational states as defined by each unique device can be entered with the Primitive command Request 10 DD where Symbol Value Device Definition DD Operational Status 00 Enter execution of instruction data type and execution of loops state 01 Enter non execution of instruction data type and execution of loops state 02 Enter non execution of instruction data type and loop state Not all devicetypes support loops Loop I nput Output modules not included NOTE Theissuing of this command to enter the non execution of instruction data type will cause specific devices to turn off or freeze their input and output systems depending on the specific device Response 10 HH Self Diagnostics Primitive Code 11 Theself diagnostic Primitive will command either the attached device or the network interface module to perform non network disturbing diagnostics The exact diagnostics executed are defined by each specific device or network interface module Request 11DD where Symbol Value Diagnostic Definition DD 00 Perform attached device diagnostic tests only 01 Perform network module diagnostic tests only 02 Perform network module and attached device diagnostic tests SIMATIC TIWAY Systems Manual Response 11
69. SEND SEQ RECEIVE SEC POLL FINAL BIT FRAME NUMBER N S NUMBER N R ad TO SOLICIT SECONDARY NSE USED BY SECONDARY TO DENOTE FINAL FRAME USED IN COMBINED STATIONS FOR CHECKPOINTING T a iae Function Bits RR RECEIVE READY 3 REJ REJECT 10 RNR RECEIVE NOT READY D NUMBERED SUPERV RECEIVE SEQ 117 RE CIERRES SUPERVISORY FUNCT P F NUMBER N R M Modifier Function Bits FRAME S 00 UNNUMBERED INFORMATION ENAM SET NORMAL RESPONSE MODE DISCONNECT REQUEST DISCONNECT UNNUMBERED POLL UNNUMBERED ACKNOWLEDGE SET INITIALIZATION MODE REQUEST INITIALIZATION MODE CMDR COMMAND REJECT SARM SET ASYNGHRONOUS RESPONSE MODE lt UM DISCONNECT MODE SARME SET ASYNC RESP MODE EXTENDED UNUMBERED MODIFI MODIFIER SNRME SET NORMAL RESP MODE EXTENDED SUPERVISORY 4 FUNCT P F FUNCTION XID EXCHANGE IDENTIFICATION FRAME M M Figure 4 15 HDLC Frame Structure 4 28 Network Architecture SIMATIC TIWAY Systems Manual Hag Fields Address Field Control Field As stated previously the opening and closing flags delimit the beginning and the end of an HDLC frame and consist of the bit pattern 01111110 HEX 7E which will appear nowhere else in the message The address field is used to identify a specific station on a network In TI WAY I for example there are 254 possible Secondary addresses When the TIWAY Primary wants to communicate with a Secondary the address of the Secondary is in
70. SIEMENS efesotomasyon com SIMATIC TIWAY Systems Manual efesotomasyon com Order Number PPX TIWAY 8101 Manual Assembly Number 2587871 0001 Second Edition ADANGER DANGER indicates an imminently hazardous situation that if not avoided will result in death or serious injury DANGER is limited to the most extreme situations A WARNNG WARNING indicates a potentially hazardous situation that if not avoided could result in death or serious injury and or property damage A CAUTION CAUTION indicates a potentially hazardous situation that if not avoided could result in minor or moderate injury and or damage to property CAUTION is also used for property damage only accidents Copyright 1995 by Siemens Energy amp Automation Inc All Rights Reserved Printed in USA Reproduction transmission or use of this document or contents is not permitted without express consent of Siemens Energy amp Automation Inc All rights including rights created by patent grant or registration of a utility model or design are reserved Since Siemens Energy amp Automation Inc does not possess full access to data concerning all of the uses and applications of customer s products we do not assume responsibility either for customer product design or for any infringements of patents or rights of others which may result from our assistance MANUAL PUBLIC ATION HISTORY SIMATIC TIWAY Systems Manual
71. SS CONTROL INTELLIGENT INTELLIGENT INTELLIGENT PC PC PC INTELLIGENT PC Figure 3 1 Distributed Industrial Control Local Area Distributed industrial control increases the effective use and reliability of Networks computers by dispersing the computing power away from a central node to positions closer to where the intelligence is actually needed However the dispersed computers must communicate with each other and this has led to the development of Local Area Networks LANs A LAN isa privately owned multiple access limited distance high speed communications channel used to move data in the form of digital bit streams between a wide range of computing devices SIMATIC TIWAY Systems Manual TIWAY Overview 3 3 32 TIWAY System Characteristics TIVAY Defined 3 4 TIWAY Overview TIWAY is an industrial Local Area Network LAN which provides a means of obtaining evaluating modifying and replacing data stored in the separate program memories of a network of interconnected operating Siemens Programmable Controllers PCs The PCs can consist of any mix of the following products e Series 500 PCs SIMATIC 520 and SIMATIC 530 e SIMATIC PM550 PCs e SIMATIC 5TI Series 102 103 PCs TIWAY is designed to satisfy today s factory requirements for data acquisition and supervisory control of manufacturing processes It is a significant enhancement of Siemens Local Line which has suppo
72. Secondary 2 after a short delay acknowledges the frame with an RR and the Primary repeats the process until Secondary 2 responds with the desired frame Notethat in the single poll technique time is lost becausethe Primary always wafts until a given Secondary has responded with the desired information before moving on I nefficiency is the major shortcoming of the single poll technique TIWAY I Circular Poll Technique Thecircular poll technique uses some of the features of the HDLC protocol to improve the efficiency of the network Theturnaround time in the secondary device can be on the order of milliseconds depending on the amount of data requested by the Primary In the PM550 CIM for example it can be on the order of 5 6 milliseconds per word requested n order to remove the PC execution time as another delay on the network TI WAY makes use of circular polling as shown in Figure 5 17 SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 29 Data Link Media Access Control Layer continued PRIMARY SECONDARY XMIT I FRAME TO SEC 1 RESPONSE DELAY XMIT I FRAME TO SEC 2 RESPONSE DELAY XMIT RR TO SEC 1 RESPONSE DELAY RECEIVE FRAME FROM SEC 1 XMIT RR TO SEC 2 RESPONSE DELAY RECEIVE FRAME FROM SEC 2 XMIT FRAME TO SEC 1 RESPONSE DELAY Figure 5 17 TIVAY I Circular Poll Technique In circular polling the Primary interleaves its requests to the multiple secon
73. See Chapters 3 and 4 Transmission of bit streams between TI WAY computing devices is half duplex The Physical layer delivers bits in the same order in which they are submitted Hectrical TI WAY electrical levels and signal encoding techniques are compatible Compatibility with those currently used by the PM 550 CIM and 990 308 for the Local Line See Referencel in Appendix C Modem interface electrical parameters are compatible with the RS 232 C specification see Reference K in Appendix C SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 7 Physical Layer continued Physical Layer Interfaces to the Physical Media Jabberstop Signal Levels Modem Interface There are two categories of interfaces to the physical media Twisted pair and modem Physical Coupling Physical coupling to the cable is by means of a connector which will provide continuous shielding for the signal lines up to the point of interconnection with the Network Interface Module Sufficient grounding is provided to protect the system against currents induced by lightning strikes to adjacent wiring but not necessarily against direct strikes tothe cable Signals are coupled between the transmission line and the transmit receive circuits in such a manner that the coupling circuit provides some level of rejection to normal AC power frequency interference Data Rates Information is transferred on TI WAY twisted pair media as follows Async
74. TE An input packet with a bad LCI is ignored by the packet layer and does not require resetting SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 37 Network Layer continued Reset Confirmation A reset confirmation packet is transmitted to acknowledge the reception of a reset request packet after reset procedures have been performed If a reset request packet has been sent and a reset request packet is received no reset confirmation packet is sent The reset request received is treated as the confirmation The format of the Reset Confirmation packet is as shown in Figure 5 21 LEAST SIGNIFICANT BIT BIT POSITION a 4 5 6 7 LCG LOGICAL CHANNEL NUMBER Figure 5 21 Fomatof the Reset Confirmation Packet Receive Not Ready Packet RNR An RNR packet is used under the following conditions 1 RNR sent the sender of the RNR is not able to receive incoming data packets on the PVC This condition is cleared by Sending a receive ready RR packet after the RNR condition is corrected Receipt of a reset request packet Sending a reset request packet After RNR is sent the sending station can continue to send data packets on the PVC 2 RNR received The receiver of the RNR cannot send data packets on the PVC The condition is cleared when A receive ready RR packet is received A reset request packet is received A reset request packet is sent and either a reset confirmation
75. TIWAY I Systems Manual Classification of Table 2 1 classifies networks by size The smallest is the Local Area Networks by Size Network which is usually but not always limited to single or multiple buildings Next in sizeis the Long Haul Network and finally interconnected Long Haul Networks Table 2 1 Networks According to Size Geographical Area Network Type 10 meters 32 feet Single Building to to 7 64 kilometers Multiple Building 25 000 feet 7 64 kilometers to Intra City 400 kilometers C is t 1248 miles ees Uy Long Haul Network 400 En eem Cross Country Interconnected i to Long Haul 10 000 kilometers 6 200 miles Cross Planet Networks SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 3 2 2 Local Area Networks Long Haul Networks Similarities of LANs to Long Haul Networks Traditional Local Communic ations Systems Table 2 1 makes a geographical distinction between Local Area Networks and Long H aul Networks There are also other differences One key difference is that legal and economic factors often force the designers of Long haul Networks to use telephone lines satellite circuits and private microwave links as the transmission media regardless of their technical suitability H owever the owners of a Local Area Network can install their own high bandwidth media twisted pair coaxial cable etc and thus achieve complete independence from all other transmission media
76. The purpose of the Presentation Layer is to perform data transformation which can take place at either the transmitting or receiving end See Figure 4 10 4 22 Network Arc hitecture SIMATIC TIWAY I Systems Manual APPLICATION LAYER COMPACTION NETWORK COMPRESSION DECOMPRESS PRESENTATION MANAGEMENT FUNCTION PRESENTATION LAYER ENCRYPTION SERVICES DECRYPTION MANAGER DATA UNIT ASSY DATA UNIT PROC ROUTING ERROR DETECT SESSION LAYER Figure 4 10 OSI Model Presentation Layer As an example a host computer on a Local Area Network might be using one set of universal codes which are sent to many different types of computing devices on the network When a message arrives at the presentation layer of a particular device the universal code must then translated into a form coherent to the receiving computer Specific examples of data transformation are e Word compaction taking a string of the same character and replacing it with a code and a byte count e Compression such as Hoffman Encoding e Encryption for security e Conversion between character codes such as ASCII and EBCDIC e File conversion between incompatible file formats e Reconciling differences between terminals for items like line length page versus scroll mode etc SIMATIC TIWAY Systems Manual Network Architecture 4 23 Open Systems Inter onnection OSI Model continued Application Layer TheApplication Layer is the user s service access
77. Thefollowing paragraphs describe the contents of this manual In order to fully comprehend TI WAY each chapter should be studied carefully Chapter 2 introduces and defines Local Area Networks The information contained here is intended to provide the background information necessary to understand the remainder of the manual Chapter 3 contains a description of TI WAY Hardware and software elements are defined as are such collateral subjects as TI WAY I s relationship to Siemens Local Line and Siemens Network Planning Service Chapter 4 presents a history and a detailed description of the I nternational Standard Organization s Open System Interconnection OSI 7 layer model for Local Area Network Architectures E ach layer is discussed separately with the features of the High Level Data Link Control HDLC operating at Layer 2 receiving special attention Chapter 5 describes each layer of the TIWAY network architecture in sufficient detail to enable a computer programmer to write the software needed for a non Siemens computer to operate as the TI WAY network Primary Chapter 6 defines many of the basic points to consider when planning and installing a TIWAY Local Area Network Overview 1 3 2 1 2 2 2 3 2 4 25 2 6 2 7 2 8 2 9 2 10 2 11 2 12 2 13 2 14 2 15 Chapter 2 Introduction to Local Area Networks Introduction ee ra raa arr n 2 2 Purpose of Section soepen tenet nn 2 2 Scope O
78. WAY poll is based on a table of active inactive Secondaries maintained by the primary for all devices on the network This tableis updated whenever the status of a Secondary changes Secondary to Secondary Communications TIWAY Secondaries cannot communicate directly with each other If data transfer is required between two Secondaries the network Primary must ask fob and receive the information and then forward it to the Secondary which needs it Network Initialization consists of broadcasting a Disconnect command to all of the Secondaries to reset their received message counts The Primary then polls all the Secondaries for a responses and the network is considered to bein a state of total disconnect The Primary then polls each Secondary with a Set Normal Response M ode command and logs the response of each Secondary in its Secondary Station Log The network has then been initialized and a record of the status of each Secondary is available in the host computer software Errors at the Data Link Level are Message Sequence Numbering Errors Checkpoint Timeout Errors Frame Check Sequence Errors and F rame Reject Errors It is the responsibility of the network Primary to recover from these errors when they do occur These errors are discussed in the context of TI WAY in Chapter 5 of this manual SIMATIC TIWAY Systems Manual TIWAY Overview 3 37 3 17 TIMAY I Primary Host Support Requirements Siemens 5100 Netwo
79. Y Systems Manual Table B 2 Data Hement Type Descriptor Field Definition TT continued 10 Drum Step Preset DSP Drum Step Current DSC 3 24 Loop Low Alarm Lamp Process Variabile 26 Loop High Process Variable 7 2 Loop Low Process Variable 28 Loop Orange Deviation 29 Loop Yellow Deviation 2A Loop Sample Rate 2C Loop Output 2D Loop Status Data Element Location Descriptor AAAA Data element types are accessed by a location number Certain data element types require specific formatting of the location Descriptor Field and are given in the following sections The first data element type has a location value dependant upon the spedific device type and data type being accessed as specified by the users manual for that device type This will allow this field to be specified from existing documentation existing for that device type For example the first I O input point in a PM550 can be specified by O and the first I O input point in a Model 530 can be specified by 1 The length of the location descriptor field is sixteen bits unless otherwise specified A descriptor of this type shall be denoted AAAA in this Appendix SIMATIC TIWAY Systems Manual TIWATI Primitives B 5 Introduction continued DCP Memory Location Descriptor Format Thelength of the drum count preset data element type location descriptor field is sixteen bits The first eight bits form the number of the drum instruction data type to be acces
80. acknowledge receipt of a data packet SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 39 Network Layer continued Receive Ready Packet Format The Receive Ready Packet packet format is shown in Figure 5 23 LEAST SIGNIFICANT BIT BIT POSITION i 7 LOGICAL CHANNEL NUMBER Figure 5 23 Formatof the Receive Ready Packet Network Layer Data Packet Header The data packet header is used to exchange user data on the Permanent Virtual Circuit PVC Send data packets are sequentially numbered using the P S parameter and the data packet carries an embedded acknowledgement to the last data packet received P R P R is the sequence number of the next expected input data packet P R and P S counters are maintained for each PVC The data packet can be sent when the following conditions exist 1 TheLCI has been assigned and the PVC is in the data transfer state 2 AnRNR has not been received 3 Thesend window is not full 5 40 TIWAY Network Operation SIMATIC TIWAY Systems Manual Data Packet Format The data packet format is distinguished by the bit value of O found in the low order least significant bit of byte 2 Figure 5 24 The data packet header is followed by a session control word and encoded destination and sourcetask IDs This is the data packet format that TI WAY Secondaries will always receive from and send to the Primary of a PVC The session control word is a fixed value and always follows
81. agraphs PRIMITIVE FIELDS LENGTH PRIMITIVE FIELD DESCRIPTOR FIELD s DATA UNIT FIELD s FIRST BIT TRANSMITTED BINARY WEIGHT LEAST SIGNIFICANT BIT MOST SIGNIFICIANT BIT Figure 5 28 Primitive Fields and Their Binary Weights Primitive Field The Primitive Field is eight bits in length which allows for 255 unique primitives Of this number the series 500 NIM currently utilizes a subset 00 01 02 03 04 10 20 30 33 32 50 51 52 Each of these is described in detail in Appendix B NOTE Theuser must refer tothe individual NIM installation and operation manual to identify those primitives utilized in that particular model NIM Primitive Code 255 FF hex is reserved for primitive field expansion SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 55 Primitive Field Definitions continued All Siemens network Primitives have been categorized into logical groups according to their function as shown in Table 5 4 Each Primitive has a request and a response format The device initiating the transaction formats a request Primitive and the device answering the request formats a responsive primitive The TI WAY I Primitive Code subset is taken from the categories listed in Table 5 4 Table 5 4 Logical Primitive Code Assignment ra Primitive Code then Function Primitives 50 5F Undefined 60 7E Field Symbols The symbols used in Appendix B to denote the different types of Primitive Descriptor Field
82. and 5 The structure of the communications package which includes the NCM the NIMs thetransmission media and all the associated software is compatible with the 7 layer International Standards Organization ISO Open Systems Interconnection Model known as the OSI model Figure 3 9 shows the various levels of software that are implemented in the network at both the TI WAY Primary and Secondaries The OSI Model is discussed in detail in Chapter 4 f Name of unit COMPUTER A COMPUTER B exchanged 7 tocol CEN Sayer EUG Application Message Presentation Message Session Message Transport Message Network Packet Data Link Frame 1pr a Layar 1 protocol Physical Bit Figure 3 9 OSI Reference Model SIMATIC TIWAY I Systems Manual Primary to Secondary Communication Secondary to Primary Communication TIVAY Software Levels A task resident in the network Primary computer at Layer 7 communicates with a task residing at Layer 7 in a network Secondary This communication takes place via the intervening software levels Data generated by the Primary task for transmission to the Secondary is passed downward from Level 7 toL evel 1 where it is transmitted to the Secondary over a physical communications line At the secondary station the reverse process takes place and the data is passed upward to the Secondary task The opposite process occurs when the Secondary station transmits to the Primary station Data generate
83. ansition in incoming signal level is sensed This transition occurs whenever subsequent bits in the serial bit stream change value i e 1 to 0 or O to 1 To maintain synchronization over extended periods of time the serial bit stream must contain these transitions on a frequent basis SIMATIC TIWAY Systems Manual TIWAY l Overview 3 29 3 11 NRZ NRZ Baseband systems require a self docking signal in each message bit stream in order to maintain overall system timing In TI WAY the recommended technique is known as NRZI Switch selected NRZ is also available to ensure full operating conformancy with the widest number of computing devices Siemens recommends use of NRZI because of its inherent clocking advantages when coupled with HDLC bit stuffing techniques NRZ is only recommended for use with synchronous modems 3 30 TIWAY Overview SIMATIC TIWAY Systems Manual 3 12 TIWAY I Relationship to the PM550 CIM Local Line Early versions of TI WAY were based on Siemens Local Line LL implemented in the PM 550 Computer Interface Module CI M and in other products such as the DS990 F our Channel Communications Controller F CCC the TM 990 308 I ndustrial Communications M odule and in the Industrial HDLC Communications Package for the DX10 Operating System Local Line Some performance characteristics of different configurations of the Local Performance Line are Characteristics e PM550 CIM Local Line installations can support a
84. anuals Excellent Good Fair Poor Accuracy Organization Clarity Completeness Graphics Examples Overall design Size Index Would you be interested in giving us more detailed comments about our manuals Yes Please send me a questionnaire No Thanks anyway Your Name Title Telephone Number Company Name Company Address Manual Name SIMATIC TIWAY Systems Manual Edition Second Manual Assembly Number 2587871 0001 Date 10 95 Order Number PPX TIWAY 8101 FOLD NO POSIAGE NEC ESSARY IF MAILED IN THE UNITED STATES BUSINESS REPLY MAIL FIRST C LASS PERMITNO 3 JOHNSON CMY TN POSTAGE WILL BE PAID BY ADDRESSEE ATTN Technical Communications M S 519 SIEMENS ENERGY amp AUTOMATION INC 3000 BILL GARLAND RD P O BOX 1255 JOHNSON CITY TN 37605 1255 FOLD SIMATIC is a trademark of Siemens AG Series 505 Series 500 PM550 5TI and TIWAY are trademarks of Siemens Energy amp Automation Inc Belden is a registered trademark of Belden Wire amp Cable Company
85. aracteristics of the modem selected SIMATIC TIWAY Systems Manual TIWAY Overview 3 5 3 3 TIWAY System Components The TIWAY system components which enable a host computer to gain access to information located in remote programmable controllers are e Network Control Module NCM This is the network Primary e Network Interface Modules NIMs These are the network Secondaries e Thenetwork media transmission lines e Software packages used by the primary host computer Figure 3 3 shows the block diagram TIWAY PRIMARY HOST COMPUTER INTERFACE TRANSMISSION MEDIA TIWAY Figure 3 3 TIVAY System Block Diagram 3 6 TIWAY Overview SIMATIC TIWAY Systems Manual 3 4 Network Control Module NC M The TWAY I Primary The TIWAY Network Control Module NCM is used as the TI WAY network Primary It functions as a communications controller with duties split between communicating on the network and interfacing with the host computer s Central Processing Unit The network can include a maxi mum of 254 NIMs attached to the Primary communication card on a single multi point line See Figure 3 4 TIWAY 1 PRIMARY HOST COMPUTER INTERFACE TRANSMISSION MEDIA NCM Figure 3 4 TIVAY System Block Diagram NCM TIWAY The TIWAY communication card governs network operation See Communication Figure 3 4 It controls which Network Interface M odule NIM may Card Functions transmit messages on the comm
86. archial addressing task identification and communication protocols are not defined in this Appendix Device type operating modes that govern which primitives are allowable are not defined in this document Device type operating modes that govern which Primitives are allowable are not defined in this document The Primitive Codes defined in this Appendix apply to all Industrial Systems Division Products that will attach to TI WAY This Appendix does not exclude other request and response Task Codes from the TI WAY network such as existing PM550 CIM but such use is discouraged The primitives that are supported in a specific device are defined by that specific device system or subsystem specification As a minimum all devices will support the primitive defined in Table B 1 Table B 1 Minimum Primitives Supported Exception Status Change State Write Block SIMATIC TIWAY Systems Manual Organization of this Appendix Applicabale Documents Basic Structure Section 2 outlines the applicable documents Section 3 defines the elements of commonl y used fields of request and response Primitives and method of expansion The Primitives and data units are defined in Section 4 along funcional needs Section 5 deals with procedural elements in using the Primitives TIWAY System Specification Document 2557706 Rev A TIWAY Protocol Specification Document 2457778 Rev B P1 PRIMITIVE ELEMENTS Primitives have the basic
87. arities of LANsto Long Haul Networks 00 cece cette 2 4 Traditional Local Communications Systems ooccooocccccncccn 2 4 Local Area Networks cc cece eee eee ee cece rara ar LAN ROMO IWS ii 5 aaron aia Madea a aaa aed ee The Hardware Elements 0 ccc teens Transmission Media 1 ieee Network Interface Hardware The LAN Software Element 0c ccc cece ee Network Topology and Media Conttol cccceeeeeeeeeeee eee eee ee n n n n n n n n n n nn 2 12 BUS TOPOlOGY MEUM 2 13 Message ThrO0UYGApUt cccccocccccccccc eee eee eee eee Message Routing 0oocccoococccocccc eee eee eee ee eee eee Sc MC PE Eror Detection scientist Edad Pn a 2 20 Redundancy iss ce e ei ieee a Pr Bele e na de rh dee d tl Rai 2 20 LAN Applications oooocccocccc anne na aa raa rr ar nna 2 23 Resource Sharing se ei ERREUR ERR A sado 2 23 Unique Features ccccocccccc nnn nnns anna naa nana ar aa ra a n n n na Contents iii 2 13 2 14 2 15 LAN AdvantageS cc cece i riuin asa hanenn n anna aa aa aaa aa rn an rn n nn 2 25 LAN Sanda S soii arado Additional Information sssse IR s 2 26 SUMMAI coccion 2 27 Chapter3 TIVAY I Overview 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 3 10 3 11 IOC UCTION 2 2 osa E hexHOx UOCE ER SERIES REA DECRE Gu EEZANGRR Ra EAE E EG OR Scope of Section sd asi nice o eae Wad Gee Wa Ga ea RR a c Terminology tesina Cena
88. ata specified in the Request Each data element location with data has to be specified Request 31TT AAAA DDDD TT AAAA DDDD gt lt gt Repeated where DDDD is defined by data element type being accessed Response 31 HH Fill Block Primitive Code 32 Fill block will replace contiguous data element locations with single specified value The starting location number of locations and data value are specified in the request Request 32 TT NNNN AAAA DDDD where DDDD is defined by data element type being accessed Response 32 HH B 20 TIWAY Primitives SIMATIC TIWAY Systems Manual Buffered Write Primitive Code 33 Buffered write will temporarily store contiguous data element locations from a given data element location with the data specified in the request in a separate memory area other than attached device memory On command the separate memory area will replace like memory area in the attached device This temporary storage area is destroyed if any other primitive accesses the attached device Request 33 CC TT AAAA DDDD DDDD lt gt lt gt Repeated where DDDD is defined by data element type being accessed Symbol CC Response 33 HH SS where Symbol SS Value 00 01 02 03 Value 00 01 Command Definition Set storage RAM null and start temporary storage of data Continue storage of data in temporary memory at address Replace attach device memory w
89. ation 5 5 5 4 Major Data Link Protocol Mechanisms The use of the Normal Unbalanced Link HDLC configuration provides for the orderly flow of information and acknowledgement between the two participating stations The controlling or responsible station is referred to as the Primary station and its transmissions are called commands Its task is to organize data flow and maintain overall control of the data link The other stations on the link are called Secondaries and the frames they transmit are called responses TIWAY uses the HDLC format with a window size of 1 to insure response time on the network and to keep buffer sizes used in the secondaries to a practical size 5 6 TIWAY Network Operation SIMATIC TIWAY I Systems Manual 5 5 Physical Layer The Physical layer is Layer 1 in the OSI Model See Figure 5 2 The following paragraphs present an overview of the TI WAY Physical layer in terms of the OSI reference model OSI MODEL TIWAY 7 APPLICATION COMMUNICATION PRIMITIVES PRESENTATION MULTI TASK SESSION SESSION MANAGER REDUNDANT TRANSPORT MEDIA SELECTION X 25 PVC USER OPTION DATA LINK NN HDLC PHYSICAL mcer RN peg pee RS 232 C LOCAL LINE Figure 5 2 TMAY I OS Model Relationships Physical Layer NETWORK The TI WAY Physical layer provides for the transmission of transparent bit streams across physical connections twisted pair modems between computing devices attached to the network
90. ations Controller This controller allows redundancy on the media It listens to both NIM input ports and processes signals arriving on either port During signal transmission the controller sends the NIM response out over the port which received the last message In this way the TIWAY Primary can select either media channel for message transmissions SIMATIC TIWAY I Systems Manual TIWAY Overview 3 11 Network Interface Module NIM continued NIM Controller TheNIM controller contains a microprocessor and a control program which enables it to process message traffic both to and from the programmable controller to which it is attached It performs signal translation functions diagnostics and communication duties with either the Interface Controller or the Dual Port Communications Controller as applicable Interface Controller Thelnterface Controller ensures signal electrical compatibility between the Network Interface M odule and the programmable controller NIM Data Rates TheNIM supports asynchronous data rates from 110 bps to 115 2 K bps as itemized below Synchronous data rates in this range can also be supported At 115 2 K bps the NIM can send or receive a byte of data every 69 4 microseconds NIM Indicators The NIM has the following visual indicators which provide its operating status to the user e Testilluminated in the self test mode e NIM Good illuminated when power is applied to the NIM and all applicable
91. ayer allows different application programs in the network Primary to communicate with corresponding programs in any Secondary The ability to have several tasks running at the sametime is particularly important in real time environments such as process control and manufacturing where it is important to react quickly to changes in real events SIMATIC TIWAY Systems Manual TIWAY Overview 3 19 TIWAY I asa Hosted Network continued Layer 6 Presentation Layer Thislayer implements a language common to all the different types of programmable controllers In a TI WAY network utilizing all the different types of Programmable Controllers 520 530 PM 550 and 5TI PCs Level 6 services give the user device transparency between all PC types For example Series 500 PCs have Task Codes which differ somewhat from those used in the PM 550 The 5TI PC does not have Task Codes at all Some common language is needed to allow a network Primary to converse with all these different PC types The Primitives make up this common language and the purpose of the Presentation Layer in conjunction with the Application Layer is to implement them Layer 7 Application Layer This layer provides the interface between the tasks and the lower levels Communication between the Primary and the Secondaries at the Application Layer is normally by means of the Primitives discussed above Figure 3 10 illustrates the relationship of TI WAY tothe OSI Model TIW
92. bus physical configuration is shown in Figure 3 15 It may consist of one or more NIMs attached to modems which are interconnected NETWORK PRIMARY NETWORK Note M Modem Figure 3 15 TIMAY I Multidrop Bus Configuration Notethat with this configuration the NCM also requires a modem 3 26 TIWAY Overview SIMATIC TIWAY Systems Manual TIWAY I Redundant Modem Multidrop Bus A redundant modem multidrop bus physical configuration is shown in Figure 3 16 below NETWORK PRIMARY NETWORK Note M Modem Figure 3 16 TIWAY Modem Multidrop Configuration With Redundancy Redundant modem configurations can only be used with NIMs which have multiple RS 232 C cards installed In the configuration shown in Figure 3 16 only one communication card NCM is active at any given time with the second communication card disabled Transport Layer OSI Layer 4 software services in the network Primary will command which communication card and therefore which modems will be used to carry any given TI WAY message SIMATIC TIWAY I Systems Manual TIWAY Overview 3 27 3 10 Baseband Signalling Two methods of data transmission in Local Area Networks are baseband and broadband In baseband the message is transmitted and received on the same frequency In Broadband a network interface unit attached to any given secondary transmits data on a specified frequency and a headend unit shifts the information to a different frequency and th
93. cal Layer Figure 4 5 represents the physical layer at either the transmitting or the Layer 1 recei ving computer Outgoing messages reach the Transmitter down the left path in the figure and incoming messages enter the Data Link Layer along the right path The task of the Physical Layer is to transport raw bits over a transmission channel This layer ensures that when one side sends a 1 bit it arrives at the other side as a 1 bit not as a O Typical questions at this level are e What voltage level equals a one e What voltage level equals a zero e How much time a bit occupies e Whether transmission is half or full duplex e How theinitial connection is established e How the connection is torn down e Thephysical design of the network connectors 4 12 Network Architec ture SIMATIC TIWAY I Systems Manual In atypical installation thetransmitter s physical layer takes bits from the layers above it modulates them onto a carrier as required by the system s operating parameters then provides the driving and isolation needed to place the signal on the transmission media DATA LINK LAYER ENCODING l DECODING PHYSICAL LAYER MANAGEMENT MANAGEMENT FUNCTION MODE CONTROL PHYSICAL CLOCKING SYNC FAULT DETECTION LAYER MODULATION DEMODULATION MEDIA INTERFACE EMIR RCVE ISOLATION TRANSMISSION MEDIUM Figure 4 5 OS Model Physical Layer When a signal is received it is demodulated by the receiving Physical Layer
94. cations requested exceeds the maximum allowed The number assigned to a data acquisition block exceeds the maximum allowed The block number requested has not been defined The number of data bytes in the requested blocks exceeds the maximum allowed The request number report by condition data type locations exceeds the maximum allowed Primitive not allowed while device is in local mode SIMATIC TIWAY Systems Manual 16 17 18 19 1A 1B 1C Data type spedified by TT has not been programmed in the attached device The attached device did not respond properly e g error in attached device communications Data type Specified by TT is not implemented in the NIM but exists in the attached device The resulting data element location specified by TT formed by the starting address plus the number of data elements to access is out of range The attached device communications is not established The store and forward buffer is full and the store and forward message discarded The data element field specified by TT is improperly formatted 80DD E xception generated in the attached device is not identified DD contains the attached device error code Native Primitive Code 01 Native allows the unique device Task Codes and data types to be accessed for a given specific device Request 01 DDDD where DDDD is defined by the task codes of the device type being accessed Response 01 HH DDDD wh
95. ce The bit stuffing bit removal is accomplished by the TI WAY hardware the Receiver Transmitter See Figure 5 6 and Figure 5 7 512 TIWAY Network Operation SIMATIC TIWAY Systems Manual Procedure Transmitter examines the frame content for five consecutive ones and inserts a zero after the fifth one Receiver examines the frame content for five consecutive ones and if the sixth bit is a one the flag is assumed If the sixth bit is a zero the zerois removed from the bit stream and discarded EXAMPLE 01111111110 TRANSMITTER 011111011110 RECEIVER 01111111110 Figure 5 6 Zero Bit Insertion BIT o 8 16 24 FLAG ADDRESS CONTROL INFORMATION SPAN OF ZERO BIT INSERTION Figure 5 7 HDLC Frame Span of Zero Bit Insertion Address Field Theaddress field will contain the destination Secondary address when sent with a Primary command and it will also contain the Secondary address when sent with a Secondary response This address is switch selectable in the Secondary See Figure 5 8 SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 13 Data Link Media Access Control Layer continued RIT 0 8 16 24 Figure 5 8 TIWAY I HDLC Frame Address Held In addition to the switch selectable address there is the broadcast address Every secondary will accept a broadcast address and not reset the send and receive sequence numbering There are 254 address combinations with the 0 addre
96. ception condition is then considered an error condition and treated as such Exceptions generated by the attached device when using the native Primitive shall return a Primitive exception whenever possible Exception when Reading The device performing the primitive operation will abort the Primitive execution upon encountering an exception condition and return the appropriate reason The device requesting the Primitive should examine the exception reason take appropriate corrective measures and attempt the Primitive Exception when Writing The device performing the primitive operation will abort the primitive execution upon encountering an exception condition and return the appropriate exception condition Exceptions concerning primitive format contents or device state will abort the entire Primitive that is to say that no data element locations have been modified Exceptions concerning the execution of the primitive are reported when they are first encountered Data element locations specified by the primitive can not be guaranteed to be unmodified or modified All the data element locations specified by the Primitive should be rewritten The device requesting the Primitive should examine the exception reason take appropriate corrective measures and attempt the Primitive P3 Length Field Exceptions Primitives in which the received number of octets for the Primitive do not match the received Length Field shall be considered an exception and di
97. computing devices isolates the entire system from normal AC power frequency interference e Continuous shielding is provided for the signal lines between the Primary and all Secondaries up to the point of interconnection with the interface modules e Local Line connectors are 9 pin D type with three large power distribution type pins active A modem interface in TI WAY is provided for modems with data rates up to 19 2K bps asynchronous RS 232 C limit and up to 115 Kbps synchronous using a clock signal from the modem Modems compatible with RS 232 C connections but with increased asynchronous data rates may also be used The user may request assistance from Siemens in selecting this hardware This interface provides control of 2 way alternate data transmission using both half and full duplex modems at both the network Primary and all Secondaries Male 25 pin D type receptacles for connection to the communications cables are provided and interchange circuit usage conforms to the standard functional descriptions given in the EIA Standard RS 232 C nterface Between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange J une 1981 Modem types are shown in Figure 3 8 SIMATIC TIWAY Systems Manual NOTE The TIWAY modem interface supports attachment of full duplex modems however in multi point configurations the secondary modems must support carrier on off control Carrier control i
98. conformant in that section Scope The first four sections of this manual contain the background information necessary to understand material covered here The intent of this section is to provide a detailed explanation of the services to be provided by the TIWAY network interfaces and an overview of the principal protocol mechanisms which are employed The material contained in this section is intended for use only by Computer Programming Specialists System Design Engineers It is assumed that such specialists and engineers have access to the references listed in Appendix C which are referred to throughout this section Topics covered here are e TIWAY relationship to the OSI Model e TIWAY Architecture e A detailed functional description of the TIWAY Physical Layer e TheTIWAY Data Link Layer including a field by field description of the HDLC Frame Format e A detailed description of the TI WAY optional X 25 Network Layer e TIWAY Transport and Session Layer capabilities e A brief description of the Series 500 Task Codes e TheTIWAY Primitives 5 2 TIWAY Network Operation SIMATIC TIWAY Systems Manual Terminology Certain terms are used throughout this manual which may be unfamiliar to those who are not conversant in data communications n some instances the definition of a new term is provided within the text but in cases where that would interrupt the flow of the information being presented the unfamiliar te
99. d SIMATIC TIWAY Systems Manual TWATI Primitives B 1 B 1 Intoduction Purpose Scope B 2 TIWAY Primitives This Appendix defines a set of user friendly Primitives for the TI WAY network The Primitives allow like data types residing in different device types connected to TI WAY and TIWAY II to be accessed in the same manner The Primitives eliminatethe need to write an information handler in the host with each unique device type connected to TI WAY Ample expansion capability will allow new data types in devices connected to TI WAY to be specified without changing the Primitive handling software The Primitives defined in this Appendix serve the basic functional needs to read and write data elements control the operating mode and ascertain the status and configuration of attached devices Primitives are defined to serve the additional functional needs of data acquisition report by condition and program modification The program modification aids offer rudimentary tools for updating an executional program E xtensive executional program modification is envisioned to occur at the host with the resulting program downloaded to the device Certain device types may have highly specialized commands or data elements which are unique tothat device type and will not generally be found in other device types Access to those commands shall be through a primitive that allows access to the unique device commands and data types Hier
100. d and receive variable N S and N R C R is set to 1 if the frame which caused the FRMR was a response frame It is set to 0 if the frame was a command frame e Byte2 Contains flags specifying the exact nature of the rejection NOTE Bit 7 is the LSB in memory and the first bit transmitted SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 19 Data Link Media Access Control Layer continued 5 20 Bit 7 W is set to 1 if the command returned in byte 0 was invalid or not implemented Bit 6 X is set to 1 if the command returned in byte O was followed by an field that is considered invalid because the command does not permit an associated field If this bit is set bit W must also be set Bit5 Y isset tolifthel field exceeded the length of the available buffer This bit is mutually exdusive with bit W Bit 4 Zis set to 1 if the command field received and returned in byte 0 contained an invalid N R count Following the receipt of a FRMR a secondary station will at its first response opportunity transmit either a UA responseto indicate that it will take action to correct the FRMR condition or transmit a FRMR response to indicate that no corrective action will be taken or that FRMR processing is not implemented In this case the field byte O will contain the FRMR command NOTE The PM550 does not support receiving a FRMR from a primary in response to its own transmission However the PM 550 will respond
101. d by the Secondary in response to a command from the Primary is passed downward from Level 7 to L evel 1 where it is transmitted to the Primary on the data link Dueto the transparency of the communications software Primary and Secondary tasks appear to communicate directly with each other A logical interface may be said to exist between the tasks in contrast to the actual physical interface that exists between the Primary and Secondary stations In the same manner logical interfaces exist between Primary and Secondary stations at Data Link line control level the Transport level and all intervening levels through L evel 7 The software functional levels are as follows Layer 1 Physical Layer Thisis the actual physical communications line connection between a primary station and the associated secondary stations Layer 2 Data Link Layer This area of the software controls the physical line in accordance with the High Level Data Link Control HDLC protocol Layer 3 Network Layer This software area controls and alternates the flow of information to and from the primary resident tasks and the various secondary level tasks Layer 4 Transport Layer n TIWAY this layer addresses alternate media selection Network hardware is designed to support redundant media for example two separate twisted pair for each NIM The choice of which lineis to be used is made at this level Layer 5 Session Layer In TI WAY the Session L
102. d for single point control of plant processes it requires no more space than a desk top That includes all of the system s components the control unit the color CRT and the printer e Host computer application By itself the 5100 is a multiprocessor based system capable of performing data analysis and report generation Where desired however the 5100 can be used as a link between a plant computer and the data base collected from the PCs After establishing a communications path between the host computer and the 5100 entire files can be transferred for additional processing or report generation e Supervisory control The 5100 also allows the operator to tune loops to achieve desired response or control load new batch recipes into PC memory download entire new programs or issue override commands Almost any control strategy needed can be implemented through user created application programs e Softwareflexibility Application programs are developed by the user via the color terminal User programming is performed in real time extended BASIC language which makes the system ideal for industrial applications While some programming experience is needed the end result can be a system customized to a user s needs which outperforms other systems with rigidly structured predefined parameters e Processing Ability The Control Unit is engineered around a 16 bit microprocessor that has a 32 bit address internal architecture for its data r
103. dancy is desired dual cable pairs must be installed These pairs should never be routed along identical paths because environmental factors disabling one cable will also disable the other Separate paths help ensure that a localized source of heat electrical interference or physical breakage will not impair communication on both cables simultaneously 614 TIWAY Cable Installation Overview SIMATIC TIWAY Systems Manual 6 9 Recordkeeping A complete detailed record of the design and routing of any network should be created and faithfully maintained in an up to date condition It should contain e Routing of the spine s e Drop cable locations e T Taplocations e Network device addresses The network record must be complete enough to trace and physically locate all cable paths and hardware components If service is required detailed records can greatly reduce the mean time to repair and troubleshoot which means less down time and more productivity SIMATIC TIWAY Systems Manual TIWAY Cable Installation Overview 6 15 Appendix A Glossary Acknowledgement A function used between peer N entities using an N protocol to obtain a higher probability of protocol data unit loss detection than provided by the N 1 layer For example acknowledgement activities between N etwork Layers in two separate computers ensure that a message stripped of data link error control mechanisms is itself correct ADCCP Advanced Data Communica
104. daries on the network in such a way that it utilizes the delay time in the secondaries to communicate with other secondaries 5 30 TWAY Network Operation SIMATIC TIWAY I Systems Manual Figure 5 17 shows the Primary transmitting a request to Secondary 1 then receiving the associated RR for acknowledgement At this point rather than repeating RR messages until a response is received the Primary immediately transmits an frame to Secondary 2 No time is wasted awaiting a response to the first frame The Primary proceeds to the third Secondary this process can go on until up to 254 secondaries the maximum number allowable on TI WAY At some future point the Primary will then come back around and poll each secondary in turn with a Receiver Ready Figure 5 17 shows that Secondary 1 has a reply ready when it receives the RR however whether this were true on an operating network would actually depend upon how much data was being requested and how many secondaries were being polled on the entire network Shown also is that the Primary then goes on to transmit an RR to Secondary 2 and receives thel frame with the requested data before renewing the sequence by again polling Secondary 1 Fromthis it can be seen that the circular polling technique has a major advantage in that it overcomes the dead or latent time in any given Secondary to communicate with other secondaries This ensures better utilization of the transmission media a
105. destined for higher layers in a particular computing device ever reach the Transport L ayer See Figure 4 8 For example the Network Layer Layer 3 in a network station can receive messages that must be routed to other places The Transport Layer never sees those messages For outgoing messages under normal conditions the Transport Layer creates a connection to the Network Layer Layer 3 for each Transport layer Layer 4 connection required by the layer above it the Session Layer 4 18 Network Architecture SIMATIC TIWAY Systems Manual SESSION LAYER B SESSION TRANSPORT MANAGEMENT NETWORK n ne ASSY E Pain DATA UNIT PROC COMM CONNECTION MNGT ROUTING MANAGEMENT PRIORITY FLOW CONTROL ERROR DET ee FUNCTION END TO END INTEGRITY CORRELATION TABLES NETWORK LAYER Figure 4 8 OSI Model Transport Layer Message Expediting Thereis a mechanism in the Transport Layer for expedited message delivery Such messages might be emergency control data coming down from the Session Layer to be sent out over the network or important data units coming in from an application such as the status of a limit switch connected to the input terminal of a programmable controller The Transport Layer can break such a message up into separate units and assign a unique number to each unit Then if the Session Layer requires fast access to a distant computer the Transport Layer can take the separate message parts and map them
106. device will enable computers manufactured by IBM DEC Hewlett Packard and others to interface easily to TIWAY The non Siemens host computer can then communicate with programmable controllers on the network as follows The host software will provide to the device the address and a command to be transmitted to the PC The TIWAY adapter device will envelop the address and command in an HDLC frame and relay it to the PC in question U pon receipt of a response the device will strip all unnecessary headers etc from the response and forward the data to the host computer The device will operate at speeds up to 38 4 Kbps on the host side and 115 2 Kbps on the network side and will use a single polling technique That is it will poll a PC and wait for a response before polling another PC Such a capability will be valuable in installations having a non Siemens computer which can be programmed to act as a TI WAY host on a network of Siemens PCs SIMATIC TIWAY Systems Manual TIWAY Overview 3 9 3 6 Network Interface Module NIM NIM Interfaces 3 10 TIWAY PRIMARY HOST COMPUTER INTERFACE TIWAY TIWAY Overview The Network Interface Module NIM is a module which occupies a slot on the chassis of the network Secondary Programmable Controller to which it is attached Each fully conformant Secondary on TIWAY has a NIM installed Internally each NIM contains a microprocessor and two media interfaces an RS 232 C int
107. diagnostics have been successfully executed e Online Extinguished if the NIM sin the Logically Disconnected State LDS Illuminated with NIM in remote but not in LDS Flashing with NIM in Local but not in LDS e Send illuminated when NIM is transmitting data e Receive illuminated when NIM is receiving data which is addressed toit e NIM PC COMM GOOD illuminated when communication is established between the NIM and attached PC 3 12 TIWAY Overview SIMATIC TIWAY Systems Manual Other NIM The TI WAY NIM Functions e Supports communications with the Primary using the TI WAY Primitives e Generates requests to its PC using PC unique task codes e Provides modem interface capability for synchronous or asynchronous full or half duplex modems e Contains jabberstop circuitry to prevent network faults due to failure in the control of the transmitting circuitry e Hasblevels of built in tests including a user initiated self test and continuous background diagnostics SIMATIC TIWAY Systems Manual TIWAY Overview 3 13 3 7 Transmission Media The TIWAY Transmission M edia interconnects the computers within the network It can be a shielded twisted pair cable or a modem line operating in accordance with EIA specification RS 232 C TIWAY PRIMARY HOST COMPUTER INTERFACE TRANSMISSION MEDIA TIWAY I Figure 3 7 TIWAY System Block Diagram Transmission Media Twisted Pair Cable A
108. ding and decoding is performed When a synchronous modem is used the modem supplied timing information on circuits DB and DD are used as specified in Reference K in Appendix C SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 9 Physical Layer continued 5 10 Indicators Indicators for the interface signals information transfer state transmission and reception are provided on the front of the Network Interface Modules An indicator will be illuminated when its corresponding signal is in the ON state Indicators are visible from the front of the unit as installed For more detailed information see the installation and operation manual for your particular NIM Controls and Switches n TI WAY switches are provided for user selection of e Data transmission rate e Local Line Modem operation e Synchronous Asynchronous Modem operation e Station address in the range of 1 to 254 Furthermore a Local Remote switch is provided on all TIWAY interface modules which when placed in Local prevents any other device on the network from writing data to or changing operational modes of the PC A momentary contact Test switch is also provided for manual activation of hardware and software self test functions For more information please see the applicable user s manual for your particular NIM TIWAY Network Operation SIMATIC TIWAY Systems Manual 5 6 Data Link Media Access Control Layer The data lin
109. dware elements and one or more multiple levels of S W software elements The Hardware The hardware elements of a Local Area Network are Hements e A transmission media such as twisted pair cable coaxial cable or fiber optics cable e A method of connecting computers to the network transmission media This is often a circuit board or a network interface module located on the computer itself These elements are shown in Figure 2 2 SIMATIC TIWAY I Systems Manual Introduction to Local Area Networks 2 7 LAN Elements continued NETWORK COMPUTING DEVICE NUMBER FOUR INTERFACE NETWORK COMPUTING DEVICE NUMBER THREE NETWORK COMPUTING DEVICE NUMBER ONE NETWORK mo mmm aMAz mo mum AMz NETWORK INTERFACE INTERFACE DEVICE NETWORK COMPUTING DEVICE NO TWO Figure 2 2 Hardware Elements of a Typical Local Area Network 2 8 Introduction to Local Area Networks SIMATIC TIWAY Systems Manual Transmission Media A LAN s transmission medium is the cable that connects all the network s components It is typically shielded twisted wire baseband or broadband coaxial cable or fiber optic cable Links between the devices on the network are either physical if they are directly connected or logical if they are connected via another node that is capable of passing data from one node to another The way messages are transmitted is determined by the type of cable used with the network Shielded Twisted Pair Wire A
110. e Window sizes are required to be the same at the Primary and the Secondary A window size of 1 means that the sender of a data packet must receive an acknowledgment for that data packet before it can send the next data packet The window size for a secondary is determined by the memory that is available for buffering input output data packets and the memory that is available for the program s required to manage these buffers NOTE TIWAY has a PVC window size of one Permanent Virtual A permanent virtual circuit is identified by a Logical Channel Identifier Circuit Initialization LCI with each secondary having a unique LCI The LCI is the concatenation linking together of the Logical Channel Group LCG and the Logical Channel Number LCN The LCG is assigned by the Network Controller Primary at network generation time It may be used to distinguish between exception log data emergency data and broadcast logical channels in the host The destination and sourcelDs aretotally Network Controller dependent The destination I D needs to be used as the source ID when the Secondary sends to the Primary on the PVC NOTE TIWAY restricts each secondary to one PVC LCIs are assigned by higher level services in the Network Controller Primary and are assigned to a Secondary through the Unnumbered Information UI command of the Data Link layer The secondary Data Link Layer must recognize this UI frame as an LCI assignment All LCI as
111. e bus Practical experience has shown that this topology can be made soreliable that the possibility of catastrophic failure can be ignored in a real world installation The mechanism for control in the bus topology varies n some networks one station is the Primary and all others are Secondaries Control of who transmits and when is determined by the Primary which polls each station on the network at specific intervals giving each a turn totransmit In the Primary Secondary arrangement no routing decisions are required by a Secondary on the network When a message is transmitted by either the Primary or Secondary it flows away from the sender to the ends of the bus The destination station recognizes any message intended for it and answers in response The bus topology can also usethe token passing scheme as described in the section below on token passing SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 13 Network Topology and Media Control continued The Ring Topology Figure 2 5 illustrates a Ring topology In the Ring topology all nodes are connected in a continuous daisy chain or ring All messages coming down the line must go through each node Packets of information are transmitted in only one direction and each node contains an active repeater that will pass the packet on to the next station Usually the transmitting node will see its own message after it has been all the way around the ring and will r
112. e network service layer in the Network Controller upon notification will close the PVC to that secondary Upon reconnection of the Secondary to the network the network service layer in the primary will reinitialize the PVC 5 42 TIWAY Network Operation SIMATIC TIWAY Systems Manual Network Layer Network layer services will be invoked after the Data Link has performed Initialization network initialization procedures and provides the active data link station address log to network layer services The network layer must then initialize a Permanent Virtual Circuit in each of the Secondaries The Logical Channel Group assignment and the use of destination and source Ds are the sole responsibility of the Network Controller SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 43 5 8 Transport Layer In TIWAY I this layer addresses alternate media selection For example a network might consist of dual twisted pairs between all interconnected computing devices The purpose of these dual pairs is to provide an alternate route for message traffic in the event the first route is disabled cable cut crushed or otherwise damaged The Transport Layer software effects this alternate route selection in all applications where such a capability is desired The Transport layer is a host function implemented in the primary software 5 44 TIWAY Network Operation SIMATIC TIWAY I Systems Manual 5 9 Session Layer In TIWAY the Ses
113. e of SECON zer enar eed E Se REESE ERR or re hee he Scope of Section nsus OR CK AUR EROR REG RATHER n Termitology Masia a A tace EE UC PEE ERA ii Communications Standards Organizations sseeeeeeeen o Intemational Consultative Committee on Telegraphy and Telephony Intemational Standards Organization 0 cc see European Computer Manufacturers Association 0 cece cee eee American National StandardsiInstitute 0 6c eee U S National Bureau of Standards 0 cece cette Electronic IndustriesAssociation tai oi ea eae Institute of Electrical and Electronic Engineers 06000 e eee Architecture Sueiro DI o ena eae heen add Examples of Layered Architecture ssssssssssseeeeee eese ComputerArchltect les siitiaina i ek etae eder a drea b or d Contents v 4 3 4 4 4 5 4 6 4 7 Chapter5 TIVWAY Network Operation 5 1 5 2 5 3 5 4 5 5 OSI Model Standard Vendor Implementations een StandardsForerunners 2 cee ehe Open Systems Interconnection OSI Model een nn nnn OSI Model FUNCTIONS cias tere eC REQUE ER ERA ERA RR ER ERR ada Layer and SeiVICes isrener nen tpe recede da Ae BR RP RE OSLSurnmaly siii Deae ede eie RET ie Race eec dr a c ae eed Rcs PhysicalLayer Layer ssssssssssseeee eee The Data Link Layer Layer2 iis radering aiaia ioiii doti ANR AARE A RA Network Layer OS
114. ecture specified in ISO DP 7498 1980 Packet Data and a sequence of control bits arranged in a specified format and transferred as an entity that is determined by the process of transmission cf Message Packet mode A manner of operating a data network by means of packet switching Packet switching The process of routing and transferring data by means of addressed packets so that a connection is occupied during the transmission of the packet only and upon completion of the transmission the connection is made available for transfer of other packets Packet switching is a combination of multiplexing segmenting and routing whereas message switching involves routing and multiplexing only A 6 Glossary SIMATIC TIWAY I Systems Manual Permanent Virtual Circuit PVC A Network facility providing a permanent association between two network connection endpoints as specified in CCITT Recommendation X 25 A PVC is analogous to a point to point private line hence no call setup or call clearing action is required or allowed Physical interface A shared boundary defined by common physical interconnection characteristics signal characteristics and functional characteristics of the interchange circuits Physical layer Layer 1 of the OSI architecture It provides for the transmission of transparent bit streams between data link entities across physical connections Physical service data units A physical service data unit consists of one bi
115. ed ad d ado dd NOISE q 6 6 Local Line Tap Spacing ococccccocccccc nennen nnn General Rules for Tap Line Installations 0 000 ee 6 7 Cable Routing 1 cc cece cece cece aaa aia i a n n n Other Considerations sigs tiris epex e rene a e eC he e Pd aee bit RoUtlhig siue eI ve chia Ce ek eae is bhi CHORO CURRO RO EO Re aciei 6 8 Installing Redundant Cables 6 9 Recordkeeping SIMATIC TIWAY Systems Manual TIWAY I Cable Insallation Overview 6 1 6 1 6 2 Introduction TIWAY is a network of computing devices interconnected with shielded twisted pair cables or with modems and telephone lines This section deals only with matters of a general nature which apply tothe installation of twisted pair cables More detailed information is contained in the individual NIM manuals For information regarding the interfacing of TI WAY network stations using modems please see Chapter 5 of this manual On the TIWAY network as many as 254 stations separate computing devices can be attached by droplines to the main trunk cable The main trunk can be as long as 25 000 feet and each dropline can be up to 100 feet The purpose of this section is to list and explain some of the major considerations which apply when planning and installing a TIWAY cabling system TIWAY Cable Installation Overview SIMATIC TIWAY I Systems Manual 6 2 Scope of Section Subjects discussed in this section are e T
116. ed in Paragraph 3 10 2 2 This redundancy extends to both the Local Line and to modems and the different physical configurations are discussed in Paragraph 3 10 2 Cable Routing Typically TI WAY cables are routed along paths which isolate them as much as possible from environmental factors such as electrical interference oil grease acids open flames steam water and any other corrosion producing substance Cables are not placed where they can be stepped on or where they rub against abrasive surfaces Sufficient grounding is provided to protect the network against lightning strikes to adjacent wiring although not necessarily against lightning strikes to the twisted pair itself Complete installation instructions for the TI WAY Local Lineareinduded in Chapter 6 of this manual SIMATIC TIWAY Systems Manual TIWAY Overview 3 15 Transmission Media continued Modem Interface 3 16 TIWAY Overview Media Transmission Rates Shielded twisted pair data transmission rates for a TIWAY Local Line are 110 bps to 115 2K bps as itemized in the following paragraph TI WAY operates at the following asynchronous data rates which are selectable by the user e 110 4800 e 150 9600 e 300 19 2K e 600 38 4K e 1200 57 6K e 2400 115 2K Synchronous data rates up to 115K bps are also supported Other Local Line Characteristics e Signal isolation between the transmission line and the transmit receive circuits in the network
117. egisters and address bus The microprocessor has the capability of executing 500 000 operations a second and has an error correcting dynamic RAM All PC communications are handled by a separate 16 bit microprocessor so the CPU is availableto execute instructions at maximum speed e Real Time Operating System The operating system is a real time multi tasking multi user operating system which allows concurrent execution of up to 16 tasks in a time slice environment The operating system also provides enhanced program development features such as a virtual screen editor prompting time of day dock and file handling commands E xecutive calls are provided for high level functions such as those used for creating and manipulating files in bulk memory e Maintainability This computer is designed for easy maintenance in the field All critical circuit boards are readily accessible by the user When power is applied a confidence test is automatically performed This routine assures that the central processor ram memory disk memory and all major circuitry are functionally operative A second test routine is provided for troubleshooting The user selects the part of thetest he wants displayed on the screen and in hard copy Both tests are supplied in the software 3 40 TIWAY Overview SIMATIC TIWAY Systems Manual 3 18 TIVAY I Performance Example 9 6 Kbps Operation In the following TI WAY performance example assume each PC is contro
118. emove it NETWORK STATIONS a ES Figure 2 5 The Ring Topology Normally the failure of a node in a Ring topology will disablethe entire system In the Ring as in some applications of the Bus an attempt has been made to eliminate the central or host station on the network without increasing the complexity of the other stations Each station on the Ring is the equal of all the others and the mechanism for control of the media in this topology varies If all stations are equal some distributed mechanism must determine which station may use the transmission lines at any given time 2 14 Introduction to Local Area Networks SIMATIC TIWAY I Systems Manual The Star Topology Figure 2 6 illustrates a Star or point to point topology As with the Bus Multi access Channel the central station on the Star can eliminate the need for each of the other stations on the network to make message routing decisions If the normal pattern of communication in the network is that of numerous Secondary stations communicating with one Primary station the Star topology leads to a particularly simple network structure However the operation of the network depends on the reliability of the central station which performs routing functions and must have the capacity to converse with all stations on the network PRIMARY STATIONS NETWORK STATIONS Figure 2 6 The Star Topology The mechanism for control in this topology involves one of tw
119. en retransmits it Other stations on the network can then receive the message TI WAY uses baseband signalling over a single transmission channel Baseband operation is currently the preferred method of transmitting data over a physical media such as a twisted pair since baseband transceivers cost less than comparable broadband transceivers and in baseband no head end equipment or multiple cables are required In networks using baseband there is full physical connectivity This means that each station on the network uses the full cable bandwidth and all computing devices in the system are connected to the same channel With sequential polling notwo stations transmit at the same time and therefore each transmitting station whether it is the Primary or one of the Secondaries can utilize the entire channel bandwidth for each message Such bandwidth advantages can be used to simplify the control structure of the communications protocols discussed in detail in Chapter 5 of this manual thereby lowering the cost of the network software as well Baseband systems require timing information to be transmitted along with the message serial bit stream in order to maintain synchronization between thetransmitter and receiver n synchronous systems the modems supply thetiming information by providing a separate dock signal to both the transmitter and receiver The transmitter will transmit a bit only when the dock is present and the receiver will o
120. entity and an N entity to co ordinate their joint operation N I nterface data nformation transferred from an N 1 entity to an N entity for transmission to a correspondent N 1 entity over an N connection or information transferred from an N entity to an N 1 entity which has been received over an N connection Interrogation The process whereby a supervisor requests another station to identify itself or give its status The process can apply to more than one station J abberstop An electrical mechanism independent of software which prevents a network computing device from hanging up a comm port when that device is in a failed condition N layer A well defined subdivision of the Open Systems architecture Each N layer is built upon the next lower layer Each layer can usethe N 1 services of the next lower layer plus its own N functions to create N services which are made available to the next higher layer Line turnaround time The time required for reversing information flow on a line in which the sending station becomes the receiver and visa versa Media access control A Data Link function which determines which station on a data highway shall be enabled to transmit at a given point in time Message A group of data and control bits transferred as an entity from a data sourceto a data sink whose arrangement of fields is determined by the data source cf Packet Message mode A manner of operating a
121. ents of this field is defined in Figure B 4 Control Register Packed The control register packed data type length is 8 bits The number of locations to access descriptor field defines the number of IR bits to be packed into one or more packed discrete control register data units Contents of this field is defined in Figure B 4 um ENS SET TO ZERO IF THE NUMBER OF IR BITS ACCESSED S LESS THAN A MULTIPLE OF 8 NEXT SEQUENTIAL IR BIT ACCESSED FIRST IR BIT NUMBER ACCESSED Figure B 4 Definition of Packed Discrete IR Data Type Word Input The word input data type length is 16 bits Contents of this field is a 16 bit hex number in which the interpretation is application dependant Word Output The word output data type length is 16 bits Contents of this field is a 16 bit hex number in which the interpretation is application dependant B 8 TIWAY Primitives SIMATIC TIWAY Systems Manual Discrete Force The discrete input output force data type length is 8 bits Contents of this field is defined in Table B 4 Control Register Force The control register force data type length is 8 bits Contents of this field is defined in Table B 4 Word Force The word input output data type length is 24 bits The first eight bits indicate the force state The last 16 bits reflect the force value as shown in Table B 5 Table B 4 Definition of Discrete Force Data Type Data Units Value Hex Data Unit Definition Off U nforced
122. ere DDDD is defined by the task codes of the SIMATIC TIWAY Systems Manual device type being accessed TIWATI Primitives B 15 Primitive Definition continued B 16 TIWAY Primitives Status Primitive Code 02 The current state of primary operational status of the device being accessed is reported by this Primitive Specific reasons for the current operational status will have to be obtained with the Native Primitive Code due to the uniqueness of each device This Primitive Code is intended to give an efficient mechanism to obtain the current operational status Request 02 Response 02DDEEFF where Symbol Value Device Definition DD Operational Status 00 Operational and performing instruction data type and loop execution 01 Operational and performing instruction data type and loop execution with a non fatal error detected 02 Operational and not performing instruction data type execution with loop execution 03 Operational and not performing instruction data type or loop execution 04 Operational and not performing instruction data type execution with loop execution and a non fatal error detected 05 Operational and not performing instruction data type or loop and a non fatal error detected 80 Not operational dueto a fatal error condition EE Auxiliary power source status 00 Auxiliary power source good 01 Auxiliary power source status not available 80 Auxiliary power source bad FF NIM Opera
123. erface card for connections to a modem and or a Local Line card for connections to a shielded twisted pair The NIM functions as an HDLC Secondary in the Unbalanced Normal Response mode see F igure 3 5 Each NIM has 3 external interfaces ports e Onetothe Programmable Controller e Twotothe network TRANSMISSION MEDIA Figure 3 5 TIWAY System Block Diagram NIM The PC interface port supports signal flow between the PC and the NIM the network ports can be configured either as Local Lineinterfaces or RS 232 C 423 modem interfaces or one of each The configuration of the network ports are user selectable as a factory option using the plug in media cards mentioned above SIMATIC TIWAY Systems Manual NIM Block Diagram The major internal components of the Network Interface Module are Analysis e RS 232 423 C interface e Local line Interface e Dual Port Communications Controller NIM Controller e Interface Controller NETWORK INTERFACE MODULE TO CONTROLLER MEDIA NETWORK CARDS COMMUNICATIONS MEDIA Figure 3 6 Block Diagram of NIM RS 232 C Local Line Cards The RS 232 C Card used with modems and the Local Line Card used with shielded twisted pair enable transmission and reception on the physical media They also provide line isolation and jabberstop control A single NIM can have two RS 232 C cards or two Local Line cards or one of each as individual requirements dictate Dual Port Communic
124. es up to 9 6 Kbps SIMATIC TIWAY Systems Manual TIWAY Overview 3 35 3 16 Functions of the Network Primary As stated previously the network Primary host computer has all the responsibility for network management This consists of e Message Flow Control e Network Initialization e Error recovery Message How The process by which secondary stations on a hosted network such as Control TIWAY are invited one at a time to transmit over the physical media is called polling Polling is one of several techniques used to control the use of a transmission media by an agreed upon protocol between computing devices trying to share a common path The TIWAY network polling sequence is shown in Figure 3 17 PRIMARY STATION TRANSMISSION FRAME TO FRAME TO SECONDARY 1 SECONDARY 2 POLL POLL Y TO PRIMAR TO SECONDARIES RESPONSE SECONDARY FRAME FROM STATION 1 E SECONDARY 1 TRANSMISSION RESPONSE ECONDARY FRAME FROM ETAHON 2 SECONDARY 2 TRANSMISSIONS TIME oO EE Figure 3 17 TIWAY I Network Polling Sequence 3 36 TIWAY Overview SIMATIC TIWAY Systems Manual Network Initialization Enor Detection and Recovery Polling TheTIWAY Primary polls all connected Secondaries on a periodic basis In a typical scheme each Secondary is contacted sequentially by the Primary and responds according to its need totransfer information report its status or indicate that it has nothing to report The TI
125. ess 64 notation Positive exponents are represented by numbers greater than 40 hex and negative exponents are represented by numbers less than 40 hex This form of notation allows exponent scan of 64 to 16 63 Examples of floating point numbers are given in Figure B 7 Exponent Value Exponent Representation hex 40 16 0 16 1 3F 16 2 42 Figure B 7 Hoating Point Examples B 30 TWAY Primitives SIMATIC TIWAY Systems Manual Primitive Summary A summary of the primitives and their formats is shown in Table B 8 Exception Response Native Configuration Request Response Primitive Format Configuration Request Response Change State Request Response Self Diagnostics Request Response Read Block Request Response Read Random Request Response Write Block Request Response Write Random Request Response Fill Block Request Response Buffered Write Request Response SIMATIC TIWAY Systems Manual Table B 8 Summary of Primitives 00 PP DDDD TT Optional 01 DDDD 01 HH DDDD 02 02 DD EE FF 03 03 HH DDDD EEEE FFFF GGGGJJJJ 04 04 NNNN MM 11 DD 11 DDDD 20 TT NNNN AAAA 20 HH DDDD DDDD EIE Repeated 21TT AAAA TT AAAA P D T 7 Repeated 21 HH DDDD DDDD Repeated 30 TT AAAA DDDD DDDD Repeated 30 HH 31TT AAAA DDDD TT AAAA DDDD lt amp gt Hno gt Repeated 32 TT NNNN AAAA DDDD
126. etter protected against unauthorized taps than are open air systems they often make future expansion of the network more difficult and expensive Open air underfloor cabling systems usually provide good access allowing maximum network expendability and flexibility 6 12 TWAYICable Installation Overview SIMATIC TIWAY Systems Manual n ceiling cable systems put to good use the empty space in open or drop tile plant ceilings Network cables are usually supported in troughs or with hooks and clamps every 10 to 15 feet Some in ceiling advantages are Flexibility Low cost e Accessibility Some disadvantages are e mpractical for buildings with enclosed ceilings e Safety hazard exists to cable maintenance personnel particularly in large installations with high ceilings e Ceilings often collect dust and other debris e Noise and work stoppages often result from the use of ladders by network maintenance personnel Surface ducting for network cabling is usually installed along the baseboards or is attached to walls at desktop height While surface ducting ordinarily protects cables from both physical and EMI effects it may also require that network computing devices be physically positioned on or near a wall SIMATIC TIWAY Systems Manual TIWAY Cable Installation Overview 613 6 8 Installing Redundant Cables TIWAY Network Interface Modules are designed to support redundant transmission media If redun
127. eway A data station which can serve as an interface to an external network Global identifier An identifier provided by the Session layer to the Presentation layer to identify a session unique within the open system environment This identifier can be used by the presentation entities for management purposes such as diagnostics and accounting A 4 Glossary SIMATIC TIWAY Systems Manual Global message A message addressed to all stations on a data highway Graceful degradation A system attribute wherein when a device fails the system falls back to a degraded but useable mode of operation rather than failing catastrophically Half duplex transmission Data transmission of N 1 service data units in either direction one direction at a time the choice of direction is controlled by an N entity e g a data circuit as a physical connection is controlled by a data link entity within the DTE HDLC High level Data Link Control procedures defined in ISO 3309 4335 6159 6256 addenda and future successors Implementation A specification of the techniques and technologies to be used within a unit and the rules governing interactions between the elements comprising that unit cf Realization Information transfer rate The average number of bits of application protocol data per second transferred from a data source and accepted as valid by a data sink N I nterface control i nformation nformation exchanged between an N 1
128. ext eight bit contain the Primitive definition and Primitive format is in the extended structure as defined in the previous paragraph The definition of the extended field will be added to this document when the need arises SIMATIC TIWAY Systems Manual B 2 Primitive Definition Primitive Assignment Rules The Primitive Field will allow for 255 unique Primitives Primitive Code 255 FF hex is reserved for Primitive Field expansion Primitives have been partitioned into logical groups according to their function as shown in Table B 6 Each Primitive has a request and a response format The device initiating the transaction formats a request Primitive and the device answering the request formats a response Primitive Each logical group is expanded in the following sections A summary of the symbols used to denote different types of Descriptor Fields is given in Table B 7 Table B 6 Logical Primitive Code Assignment Exception and Status 00 0F Program M odification Aids 40 gt 4F Function Primitives 50 gt 5F Undefined 60 6E Table B 7 Summary of Field Symbols Symbol AAAA Data Element Location DDDD Basic Data Element LLLL Length Attached Device Status NN or NNNN Number of Locations PP Primitive Code Data Element Type SIMATIC TIWAY I Systems Manual TIWATI Primitives B 13 Primitive Definition continued Exception and Exception Primitive Code 00 Exceptions found in the interpretation Status Primit
129. f these seven layers is provided in Chapter 4 e Application This top layer provides services that directly support user and application tasks and overall system management e Presentation The next layer translates encoded data into formats useful to the application e Session The session layer enforces dialogue rules and procedures between users of an established session e Transport Thetransport layer provides end to end control of a communication session once the path has been established e Network Here the messages are addressed the path is established and the flow of the messages between the nodes is controlled e Data Link This layer manages access to and use of the channel and ensures the proper sequence of the data Prime duty is to ensure reliability of message traffic e Physical The lowest layer is typically the hardware including interface devices modems and communications lines involved in transporting serialized binary information Additional For a more detailed discussion of the following standards organizations see Information Chapter 4 2 26 Introduction to Local Area Networks SIMATIC TIWAY I Systems Manual 2 15 Summary LANs arethe communication systems of the 80 s There are currently a large number of networks and network vendors entering this new market Standards are evolving and will stabilizein duetime For the present the lack of universal standards will allow new technologies to e
130. g The maximum number of bytes of user data sent in any one message is 273 The window size for TI WAY is one which means that a message received by any station on the network Primary or Secondary must be acted upon and answered before the next message is sent Higher level services must provide for message segmentation and reassembl y The operation of the NIM involves certain timing considerations that must be adhered to in order to insure proper operation of the TI WAY network NIM Response Delays TheNIM requires a delay period after receipt of a frame to decode the frame build an appropriate HDLC response and set up the necessary hardware to transmit the response If no transmission errors occur this delay is 600 microseconds for the worst case where the NIM receives an HDLC I FRAME and responds with al FRAME The TIWAY primary should allow for the NIM response delay and should establish a secondary timeout period greater than this delay 5 26 TIWAY Network Operation SIMATIC TIWAY I Systems Manual Media Access Control Hierarchy Supervisory Scan Primary Transmission Delays TheNIM alsorequires a delay period of 600 microseconds after transmission of a frame to set up the necessary hardware to receive the next frame from the TI WAY primary In TI WAY networks with more than one secondary a polling scheme may be implemented to minimize the impact of the setup delay by communicating with other secondaries while a part
131. ger Values 3 42 TIWAY Overview SIMATIC TIWAY Systems Manual 3 19 Network Planning Service NPS A network planning service offered for a nominal fee by Siemens offers a cradle to maturity service There are four levels of service available NPS is intended to complement services already provided by Siemens Application Engineering Distributors AE Ds Level One This level provides an audit function For a nominal fee Siemens will send its technical representatives on site to audit the fundamental networking requirements of any projected factory installation Siemens will then recommend the network configuration which in its best judgement will accomplish the job and will doa timing analysis of the proposed installation to establish the exact operating characteristics of the proposed installation Upon completion of Level One equipment can be ordered and installed through the appropriate AED Level Two For a minimum charge Siemens will provide all necessary technical assistance required for network initialization and startup This service level will be provided after network installation is complete Level Three Level Three services provide continuing support and maintenance for an installed operating TI WAY network on a prearranged contractual basis Level Four L evel Four services encompass all other levels and are performed by the Siemens Contract Systems Branch CSB Users purchasing a L evel Four NPS will be pro
132. hronously at user selectable baud rates of 110 150 300 600 1200 2400 4800 9600 19 2K 38 4 57 6 and 115 2K bits per second Clock Encoding and Extraction NRZI encoding is employed in TI WAY to provide a self clocking signal into and out of the Physical Layer of the transmitter and receiver stages A logic ONE is transmitted as a nontransition i e notransition of the line state during the bit cell A logic ZERO is transmitted as a 1 0 or 0 1 transition at the nominal center of the bit cell The Physical layer contains a timeout jabberstop mechanism which ensures that the transmitter does not remain turned on longer than twice thetime required to send the maximum length message Signal levels for twisted pair cable interfaces are compatible with those for the Local Line as specified in reference H in Appendix C The Physical layer in TI WAY provides an interface to low speed modems with data rates below 20 Kbps The modem interface provides standard signals as defined in Figure 5 3 for the control of two way alternate data transmission using both half and full duplex modems The modem interface also provides isolation and protection of the internal circuitry of the programmable controller as previously discussed 5 8 TIWAY Network Operation SIMATIC TIWAY Systems Manual The modem interface is a standard Type E DTE configuration as defined in Chapter 5 of EIA RS 232 C Reference K in Appendix C This interface utili
133. iaceo rack qud AR E EUR Factors Promoting Distributed Control Local Area Networks iced ubere baee eoe ded e VOCE ea dis ed GR Radon TIVAY I System Characteristics 0 0occccccc rnm TIWAY Defined 252 oto aa na DR Rc rdc TIVAY I System Components 2c cece eee eee Network Control Module NCM The TIWAY I Primary ennnnnn n n nnn TIWAY Communication Card Functions ssssssse Ren 3 7 Non Siemens Computer Interface Module The TIWAY Adapter Network Interface Module NIM seen mmm nnn NIM INCE ACES ie cp buie kn MERERI b CREE ED acia ea i EAE NIM Block Dia gram Analysis NIM Data Rates sis caida iaceo C ceca o ec RO e Cice Oa cc C ee E Cab ne NIME Indica tols gt taa Te coe SRL Ee redii ae diia OtherNIM Functions oococccoccncc RII raa Transmission Media nnn hh a Twisted Pal Cable 1 124 tad dece de Ede te e Ee Be dad lid hive dei b bed Modemilnteiface ecco rice Ducere Rr Cea E dad Network Control Module tiec eec he di de dett E ADR TIVAY I asa Hosted Network ccc cece eee hh naar rara rara ranas OS Modele eie e Ata eddie cercasi rada cid Primary to Secondary Communication Secondary to Primary Communication TIWAY I Software Levels hh TAY IO POGY soos kceehr ka AGRO ari dad SE RER s Ra TIWAY Bus Characteristics isa es bu ite a eae eee been Pc da Bus Configurations of TWAY isssssssssssssee eee ems Baseband Signalling
134. icular NIM that has just responded is setting up to receive again When operating the NIM in the asynchronous mode it is recommended that the TIWAY Primary delay after receipt of a frame from one secondary before transmitting a frame to another secondary on the network This delay should be greater than the time required to transmit 8 bits of data at the operating data rate This will insurethat each NIM on the network receives an HDLC ABORT which will serve to synchronize the NIM s receiver to the Primary s transmission when it occurs Media access is granted by the Network Controller to a secondary with the poll bit set to one The Secondary must respond tothe Primary within the acceptable NIM Response Delay period If the response is not ready for transmission the Secondary can respond with an RNR or RR If the Primary does not receive a response within the NIM Response Delay period window it will proceed with checkpoint error handling and either advance tothe next station or retransmit to the Secondary not responding The Secondary cannot respond tothe receipt of a good frame outside of the NIM Response Delay period It must wait until the next poll cycle If the Secondary receives an error frame it will respond with the appropriate action The Network Controller Primary in TIWAY must poll all secondary stations on a periodic basis The poll includes stations already in the ITS state or DISC state as well as any stations that have
135. il at the top only the data remains Each layer has its own protocols and the set of layers and protocols is known collectively as the Network Architecture Figure 4 4 illustrates this process OUTGOING FRAME INCOMING FRAME CONSTRUCTION REDUCTION 328 APPLICATION APPLICATION PRESENTATION PRESENTATIONI SESSION SESSION TRANSPORT TRANSPORT NETWORK NETWORK DATA UNIT FIELD DATA LINK PSCA PHYSICAL COMMUNICATIONS PATH PHYSICAL TRANSMISSION MEDIA Figure 4 4 OSI Model Frame Construction and Reduction SIMATIC TIWAY I Systems Manual Network Architecture 411 Open Systems Inter onnection OSI Model continued OSI Summary In layered architecture all services are built upon the basic interconnection provided by the transmission media which may be considered as Layer O of the ISO Model The names of each of the seven layers of the model and the typical services provided by each layer are shown in Table 4 2 Table 4 2 Layers and Services 7 Application User Programs 6 Presentation Character Set and Data Type Conversions po Re a O 1 1 c 5 Session File Open Transfer Close Message Blocking 3 Newok Message Routing and Switching Store Forward 2 Datalink Framing Error Control Addressing NOTE Layers 1 through 4 are concerned with traffic movement through the network layers 5 through 7 are concerned with message handling within the transmitting or receiving computer Physi
136. ink media access control layer SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 49 TIVAY I Presentation and Application Layers continued e sii FLAG ADDRESS CONTROL INFORMATION PRIMITIVE STRUCTURES COMMAND FORMAT LENGTH dr de DESCRIPTOR FIELD s DATA UNIT FIELD s RESPONSE FORMAT LENGTH AS SECONDARY STATUS DATA UNIT FIELD s Figure 5 26 Basic Primitive Structure 5 50 TIWAY I Network Operation SIMATIC TIWAY Systems Manual The maximum length of the descriptor and data unit fields is 270 bytes for TIWAY network interface modules installed on programmable controllers The 270 bytes exdude the primitive code and protocol control fields Other devices connected to TI WAY may support frame lengths in excess of 270 bytes The actual length supported is dependent on device type and must be ascertained with the Primitive Format Configuration Primitive The length field of a TIWAY Primitive consists of sixteen bits which indicate the number of octets in the Primitive Primitives in which the recei ved number of octets for the primitive field do not match the received Length Field shall be considered in error and discarded A Primitive exception response will be returned to indicate the error FIRST BIT TRANSMITTED LEAST SIGNIFICANT BIT MOST SIGNIFICANT BIT Figure 5 27 Binary Weight of the Fields SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 51 5 11 Basic Procedure Rules In order
137. ion when two or more stations are contending for use of the transmission media e Performs error recovery NOTE TI WAY has adopted the internationally accepted HDLC High Level Data Link Control for the Data Link Layer SIMATIC TIWAY Systems Manual Network Architecture 415 Open Systems Inter onnection OSI Model continued Routing Functions On areceiving computer there is some routing between the different frame types An acknowledgement frame for example from one network station acknowledging receipt of a message would be routed to the M edia Access Control Sublayer whereas data frame would be routed to the Logical Link Control sublayer Network Layer A primary function of this layer is to accept outgoing messages from higher OS Layer 3 layers in the transmitting computer convert them into packets and ensure that the packets are sent toward the proper destination If a message from Computer A is meant for Computer H for example this layer makes certain the message is routed to Computer H even if it travels on the network via numerous secondary nodes See Figure 4 7 TRANSPORT LAYER INTERNETWORK ROUTING NETWORK MANAGEMENT NETWORK FUNCTION LAYER INTRA NETWORK A Do ua ROUTING ROUTING REPORTING ERROR DETECT RECOVERY NETWORK A m NETWORK X mu EDS IT Figure 4 7 OS Model Network Layer 4 16 Network Architecture SIMATIC TIWAY Systems Manual There are typically twotypes of routing performed
138. is approach practical Siemens is pursuing this approach through its semiconductor resources TI WAY II is designed to exploit these advantages Contention Contention is also known as Carrier Sensed Multiple Access CSMA It provides controlled access to the network where the nodes must detect whether there is a carrier signal on the line before they can access it This method is basically a listen then speak scheme in which each node listens until the lineis clear then speaks If two nodes try at the same time to access the line a collision results Both nodes terminate their access attempts perform a random delay and then retry Since it does not support guaranteed delivery of a message within a fixed time period during peak loading on the network Siemens does not recommend this approach for industrial control applications 2 16 Introduction to Local Area Networks SIMATIC TIWAY I Systems Manual Polling In polling each LAN station is rigidly controlled so that only one of them sends information along the line at any given time Polling is done by a network Primary which sends a control message to each station in turn inviting it to transmit The station replies with information status or a message indicating it has nothing to report When polling is done in this way flexibility is obtained because the computer may reorganize the order of polling should this become necessary Further some nodes may be allocated more than one p
139. is is possible because the Network Interface Modules can memorize data locations that are repeatedly accessed in a data acquisition scheme Certain Primitives enable a user to goin and access a block of data previously defined and stored in the PC 5 48 TIWAY Network Operation SIMATIC TIWAY Systems Manual Primitive Functions The primitives defined in the following paragraphs serve the following basic functional needs e Read and write data elements e Control the PC operating mode e Ascertain the status and configuration of attached devices e Data acquisition e Report by condition e Program modification Certain TIWAY computing devices such as the PM550 may have highly specialized commands or data elements found in no other device type Access to those commands and data elements is assured by a Primitive which enables the use of the Task Code unique to the particular device In other words if a programmer wants to perform an action in a secondary and that action is not possible using a Primitive the appropriate Task Code itself can be sent down using the Native Primitive Primitives have the basic structure shown in Figure 5 26 Thereis a Command Format and a Response Format as shown The binary weight associated with the definition of the fields is detailed in Figure 5 27 The minimum length of any field is 8 bits with a minimum field increment of 8 bits This will allow for octet testing of data link frames at the data l
140. ith storage memory Abort temporary storage memory Command Definition Temporary storage memory is reserved Temporary storage memory is not reserved Program Modification Aids Programming modification aid primitives operate only on the instruction execution data type Attempts to use program modification aid primitives on other data types will result in an error SIMATIC TIWAY Systems Manual TIWATI Primitives B 21 Primitive Definition continued B 22 TIWAY Primitives Locate Primitive Code 40 Locate will find a specified data pattern in instruction execution memory and return its location A mask is provided to specify which bits of the 16 bit data pattern are to be included in the locate operation A starting location is provided to allow the locate operation to start at any arbitrary location The locate operation will examine all the memory locations starting with the requested location to the end of instruction execution memory and restarting at the beginning of instruction execution until the requested starting location is encountered The locate operation will terminate either when the requested data pattern is found or when the find operation fails to locate the requested data pattern Request 40 AAAA DDDD EEEE where DDDD is a 16 bit data pattern and EEEE is a 16 bit mask A one in the mask indicates that corresponding bit in DDDD is to be included in the find operation Response 40 HH AAAA DDDD whe
141. ive of a primitive or during the execution of a Primitive shall be reported with Codes this response Primitive Request There is no request defined for this Primitive Response 00 PP DDDD TT lt gt Optional depending on exception where PP is defined as the request primitive that contains the exception where DDDD is defined as U O UJ D gt O NO OUBWNFO enm 11 12 13 14 15 B 14 TIWAY Primitives Primitive is not implemented Data type specified by TT is not defined in the attached device Data element location Specified by TT is out of range Primitive has excess data unit bytes Primitive has insufficient data unit bytes The number of information bytes received does not match the number of information bytes specified in the length field Device in wrong mode for primitive execution User program in device has disabled communication to network communication module Lockout bit Written data type location specified by TT did not verify Data type location specified by TT is write protected Device fails to respond Primitive aborted due to a fatal error condition in the specific device addressed Data type specified by TT now has an invalid value due to primitive execution An error was encountered while executing the requested primitive with the specified data type TT Primitive not valid for the specified data type TT Data pattern requested was not found The number of lo
142. k protocol provides for the transmission of commands and responses induding data between correspondent network products with substantially lower error rates than provided by the Physical Layer See Figure 5 4 OSI MODEL TIWAY 7 APPLICATION COMMUNICATION PRIMITIVES PRESENTATION SESSION SESSION MANAGER TRANSPORT Le MEDIA SELECTION X 25 PVC NL INN RS 232 psu E cua LINE NETWORK Figure 5 4 TIWAY I OS Model Relationships Data Link Layer The unbalanced configuration a single Primary station and multiple Secondary stations Normal Response M ode Secondary station may transmit only when explicitly enabled by the Primary Module 8 nonextended sequence numbering and the Unnumbered Information UI for use as a global address without impacting the send and receive sequence number variables See Chapter 4 of this manual A TIWAY network can be configured for point to point operation for multi point operation or a combination of the two Multi point operation consists of a primary station plus one or more secondary stations operating in the Normal Response M ode SIMATIC TIWAY Systems Manual TIWAY Network Operation 511 Data Link Media Access Control Layer continued Link Control The TIWAY command response handshake between the network Primary Protocol and any given Secondary provides for a flexible and orderly flow of information and acknowledgement between the two participating stations with one station
143. length greater than seventeen Data Link Enor Errors at the Data Link layer consist of sequence numbering errors Detection and checkpoint timeout errors Frame Check Sequence F CS errors Frame Recovery Reject errors FRMR and Length Field errors Sequence Numbering Errors Sequence numbering errors occur when the receiving station receives an FCS error free frame and it contains an N S sequence number that is not equal to the expected receive variable R at the receiving station The receiving station does not increment its receive variable and discards any subsequent frames with sequence numbers greater than thel frame in error The receiving station may either use the Frame Check Sequence Error described for recovery or issue a REJ command with the N R set to the received frame that was in error for retransmission Checkpoint timeout Errors Timeout mechanisms are provided beginning with the transmission of a frame with the P bit set to one and ending when either a frame is received with the F bit set to one or the ti mer expires waiting for a response Recovery consists of retransmission of all unacknowledged frames with the sequence numbers less than the set S variable at the time the last frame with the P set to one was transmitted Secondaries will not retransmit unless explicitly granted access to the transmission media by the Primary 5 24 TIWAY I Network Operation SIMATIC TIWAY I Systems Manual Frame Check Se
144. lling and or monitoring the following points e 64 discrete devices such as valves pumps etc with 2 bits of feedback status per device e 32 discrete status or alarm inputs such as limit switches level Switches etc with 1 bit per device e 32 analog inputs 16 bits with 6 level alarm status 8 bits with alarm status categories of BAD HIGH HIGH HIGH HH HIGH H LOW L LOW LOW LL BAD LOW e l6integer results from calculations totalizers etc Also assume the TI WAY user wishes to download a 128 word recipe to each PC hourly A typical poling scheme is shown in Table 3 1 Table 3 1 TIVAY I Polling Scheme Data Bytes Period e 1 SN GEM Discrete Status with alarm 2 Sec Analog Inputs with status 96 2 Sec Integer Values 32 10 Sec Communicating at 9 6 Kbps with each PC monitoring the above points a TIWAY network would support e 14 530 Programmable Controllers or e 12 PM550 Programmable Controllers For a Total System of 530 PM550 896 768 Discrete Devices 448 384 Discrete Alarms 448 384 Analog Inputs 224 192 Integer Values SIMATIC TIWAY Systems Manual TIWAY I Overview 3 41 TIWAY I Performance Example continued 115 2 Kbps At 115 2 Kbps with each PC monitoring the points listed a TI WAY Operation network would support e 191530 PCs or e 168PM550 PCs For a Total System of 530 PM550 12224 10752 Discrete Devices 6112 5376 Discrete Alarms 6112 5376 Analog Inputs 3056 2688 Inte
145. locks are specified through a 32 bit mask as shown in the request Primitive The total number of bytes returned may not exceed the maximum size specified for that device type The response Primitive will return the data associated with the requested blocks starting with the lowest number block increasing to the highest number block A data block separator is not provided in the response Primitive Request 51 EEEEEEEE where EEEEEEEE is 32 bits defined as NUMBER 20 HEX BLOCK NUMBER 1 Response 51 HH EEEEEEEE DDDD DDDD DDDD DDDD EE gt Erica gt Repeated where EEEEEEEE is mask as defined by the request Primitive and DDDD is defined by the data type being accessed The order of return of the blocks is from the lowest numbered block to the highest For example if block numbers 2 4 and A were requested in the request Primitive the first data block in the response Primitive is data associated with block number 2 the next data block associated with block number 4 and so on B 24 TWAY Primitives SIMATIC TIWAY I Systems Manual Write and Gather Primitive Code 52 The write and gather Primitive specifies which blocks defined by the define Primitive will be read and allows replacing of contiguous data element locations not associated with the blocks defined by the define primitive The blocks are specified through a 32 bit mask as shown in the request Primitive The total number of words in each of the reques
146. lr A dap Contents List of Tables 2 1 Networks According to Size o ooooccccoccnccnn eee 2 3 3 L TIWAY lI Polling Scheme ores cer beet ente Ee R beads Vrbe re beens ce ea edad 3 41 J L AICDIECIUIBS is wna eres nee deur s P Ras ee rack ach ed place og as E y emcees 4 2 Layersand Services isssssssssssssssssss esses nn 4 12 5 1 TIWAY I Command Response SubsetS 0 ccc cect ees 5 21 5 2 Encoding of Command Response Field 0c cece ected 5 21 5 3 Diagnostic CodeS cies ma ate er eee e ce pcne ec o Real acc AT Ra x a S RS 5 36 5 4 Logical Primitive Code Assignment 0 0 i cc een 5 56 5 5 Summary of Field Symbols umi ii aet n IP Rte E n AT e 5 56 5 6 Series 500 NIM Primitive Code Subset 0 cece ees 5 57 B 1 Minimum Primitives Supported 1 m ee ERR TH HX ER RACE ER TR B 2 Data Element Type Descriptor Field Definition TT issssssssssse eren B 4 B 3 Definition of Discrete IR Data Type Data Units 0 B 4 Definition of Discrete Force Data Type Data Units ssssssssssseseeereeeeee B 9 B 5 Definition of Word Force Data Type Data Units 0 0 00 ee B 6 Logical Primitive Code Assignment ssssssssssssss eese eese B 13 EZ Summary of Feld Symbols seis iris B8 Summary Of PUEDES cay para econ inde caver Peep honors esce Aras eed a a Ra UD Contents xi Chapter 1 Overview 1 1 IntiGducBori iuri vk 6x cp Rev excu ib re exu a ERE RANGE IE ERE E 1
147. man activities Computer networks such as TI WAY are organized into layers which help reduce their design complexity Each layer offers a service to the layer above it The layers and their corresponding protocols are called collectively the network architecture SIMATIC TIWAY Systems Manual Network Architecture 4 7 4 3 OSI Model Standard Vendor Implementations TI WAY s architecture is an adaptation of the OSI Model and it is but one application of that model The widely varying implementations of the OSI 7 layer model are shown in Figure 4 2 Thefirst six are those made by some of the standards organizations previously discussed The remaining three are vendor private company implementations CLEARING NAU HOUSE SERVICES FILE SVC PRINT SVC PRESENT PRESENT l ISO ENT ACCESS COURIER PROTOCOL SERVICES PROTOCOL i CONTROL ISO PROTOCOL E 2083 TRANS MISSION TRANSPORT CONTROL TRANSPORT ISO PROTOCOL ad i NETWORK iNTERNET SERVICES CONTROL PROTOCOL INTERNET 4083 SDLC DATA LINK DDCMP BSC ETHERNET VARIABLE VARIABLE EIA EIA CCITT CCITT Figure 4 2 OSI Model Standard Vendor Implementations Standards Some of the vendor implementations shown were the forerunners of the Forerunners standards themselves F or example the predecessor to most network architectures was the Systems Network Architecture SNA by IBM IBM also developed Synchronous Data Link Control SDLC and sub
148. may not contain an field 5 16 TIWAY Network Operation SIMATIC TIWAY I Systems Manual Summary of Control Fields A summary of the command response set that is supported by TI WAY is as follows e CandR are used to indicate the use of the field as a command C or response R e NandU are used below to indicate whether the command is a Numbered Supervisory command or an Unnumbered Control command e Xindicates that previously transmitted frames that are unacknowledged when this command is actioned remain unacknowledged and the message sequence numbers N S and N R are reset to zero e indicates than an field is permitted with the command response Information transfer Indicates that the frame contains an Information field after the command response field The format of this field is not defined C R I RR Receive Ready Command response indicating that an frame is acknowledged or that the primary or secondary is ready to receive an I frame C R N REJ Reject Used by the primary or secondary to request retransmission of frames starting with the frame numbered N R I frames numbered N R 1 and below are acknowledged C R N RNR Receive Not Ready Used by the primary or secondary to indicate a busy condition The station is temporarily unable to accept additional frames C R N UA Unnumbered Acknowledge Receipt of an unnumbered command is acknowledged R U SNRM Set Normal Response
149. me important characteristics of computer networks are e A network usually consists of a several cooperating computers running independently at different processing centers on the network e Theuser need not be aware that that there are multiple processors e Theuser man to machine interface allows a common access to all the processors on the network e Any needed resource service or data can be accessed by sending an appropriate message to the appropriate location Network architecture is the set of layers and the protocols associated with each layer There are uniform communications mechanisms operating between all devices on a Local Area Network These mechanisms are compri sed of the services which are performed at each layer of the network communications system and of the protocols governing the cooperati on of peer entities at each layer These mechanisms make up what is called the Network Architecture The purpose of this section is to provide background information about current work toward network standards This will enable a user to understand how the architecture and protocols of TI WAY Local Area Network fit into the International Standards Organization s OSI Model Before studying this section the reader should read and understand Chapters 2 and 3 The subjects covered in this section are e Communications Standards Organizations e Introduction to architectures e Introduction to the OSI Model e Layers of the
150. ment type 3 Theexecution of a Primitive 5 52 TIWAY Network Operation SIMATIC TIWAY Systems Manual The exception reason is returned with the exception Primitive which is Primitive Code 00 The procedure taken is dependent on the Primitive used There are two classes of procedures used for exception handling 1 Procedures which are associated with reading data elements 2 Procedures which are associated with writing data elements An attempt counter should be maintained by the Primary and the Primitive should be aborted after a predefined number of attempt failures The exception condition is then considered an error condition and is treated as such NOTE Exceptions generated by the attached device when using the Native Primitive will return a Primitive exception whenever possible Exception when Reading The device performing the Primitive operation will abort the primitive execution upon encountering an exception condition and will return the appropriate reason The device requesting the Primitive should examine the exception reason take appropriate corrective measures and reattempt the Primitive Exception when Writing Exceptions concerning Primitive format contents or device state when writing will abort the entire Primitive Exceptions concerning the execution of the Primitive in the addressed device el ements in locations specified by the Primitive cannot in this case be guaranteed to be either modified or not
151. ments between sampling of the data element type location A zero value defines a variable sample rate subject to NIM load where CC is defined as CC compare report number condition definition type type of DDDD 1 equal poll 1 when the indicated location is equal to DDDD 2 notequal poll 1 when the indicated location is not equal to DDDD 3 exceeds poll 1 when the indicated location has a value greater than DDDD 4 under poll 1 when the indicated location has a value less than DDDD SIMATIC TIWAY Systems Manual 71 72 73 74 75 76 FF outside within equal not equal exceeds under outside within suppress Response 53 HH SIMATIC TIWAY I Systems Manual poll poll init init init init init init when the indicated location has a value less than the first DDDD or greater than the second DDDD when the indicated location has a value exceeding than the first DDDD and less than the second DDDD when the indicated location is equal to DDDD when the indicated location is not equal to DDDD when the indicated location has a value greater than DDDD when the indicated location has a value less than DDDD when the indicated location has a value less than the first DDDD or greater than the second DDDD when the indicated location has a value exceeding than the first DDDD and less than the second DDDD the indicated location is no longer to be monit
152. merge although the number and types of networks will begin to decline as standards or defacto standards are accepted The cost of LANs will decrease as more very large scale integration is implemented Several types of networks such as Baseband and Broadband with bus and ring topologies should emerge Most large networks of the future will probably be internetworks of several types of networks interconnected by gateways No one network will optimally meet user requirements and this is why Siemens is working on two industrial network families TI WAY and TI WAY II Broadband backbones will interconnect several buildings at one site X 25 gateways or special links will tie various regional areas together High speed Metropolitan Area Networks MANs will interconnect buildings within a city Communication has evolved to meet the changing needs of people as long as there have been people Computers are becoming the caretakers of modern day information exchange and with this change we are seeing the birth of the local area network a response to the need for machine to machine communication These networking systems meet the need people have to communicate via computer in a fast moving world requiring increased productivity and higher quality SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 27 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 3 10 3 11 3 12 3 13 3 14 3 15 3 16 3 17 3 18 3 19 Chapter 3 TIWAY
153. mitted it to ANSI and ISO for adoption as both the U S and the international standard ANSI modified SDLC and renamed it ADCCP for Advanced Data Communication Control Procedure ISO modified it and called it HDLC High Level Data Link Control CCITT modified it and called it LAP for Link Access Procedure LAP became part of the X 25 standard although CCITT later modified LAP to LAPB in order to make it compatible with a later version of HDLC Today HDLC and its derivatives arethe most widely used of the Data Link Layer protocols Other vendor applications of the ISO Model include DECNET by Digital Equipment Corporation and Ethernet by Xerox 4 8 Network Architecture SIMATIC TIWAY I Systems Manual 4 4 Open Systems Interconnection OSI Model The model for TI WAY architecture is the Open Systems Interconnection OSI model of ISO Open Systems are those which are open to each other due to their mutual use of applicable standards just as a letter written in English is open to anyone who reads English The following paragraphs explain each layer of the OSI Model SeeFigure 4 3 APPLICATION gt INTERNATIONAL STANDARDS SERVICE SELECTION PRESENTATION DATA TRANSFORMATION SESSION INTERACTION COORDINATION TRANSPORT END TO END INTEGRITY NETWORK ROUTING SWITCHING DATA LINK FRAMING ERROR DETECTION PHYSICAL DATA TRANSMISSION ORGANIZATION ISO TECHNICAL COM MITTEE 97 SUBCOMMITTEE 16 LOGICAL PART
154. modified Therefore when the exception condition is returned to the sender all data element locations in the addressed device specified by the failed Primitive should be rewritten The station originating or sending the Primitive should examine the exception reason take appropriate corrective measures and reattempt the Primitive SIMATIC TIWAY I Systems Manual TIWAY Network Operation 5 53 Basic Procedure Rules continued 5 54 Error Procedures Theerror procedure is used when the communication protocol services operating at lower layers on the network report that a reliable data link cannot be established or that the data link previously established to the addressed device has been lost Exact error conditions of this nature are dependent on the error reported from the lower level The errors will fall into two classes 1 Thenetwork is incapable of transferring information 2 The addressed device has failed to respond reliably An attempt counter should be maintained in the sending device and the Primitive should be aborted after a predefined number of attempt failures The error condition is flagged and further operations are dependent on supervisory control functions TIWAY I Network Operation SIMATIC TIWAY Systems Manual 5 12 Primitive Field Definitions Thelocations and binary weights assigned tothe Primitive fields are given in Figure 5 28 below Each of the basic field types shown is described in the following par
155. nal bit set to 1 and Primary can then transmit a message The Primary subsequently leaves the Poll bit unset until the last message in the series when it sets the Poll bit to 1 signalling the Secondary that all the traffic has been sent and the Secondary can respond The Poll Final bit can be used in combined stations likethose discussed in Figure 4 14 for Checkpointing error detecti on SIMATIC TIWAY Systems Manual Network Architecture 4 29 HDLC Frame Structure continued Frame Check Sequence FCS Field The final three bits of the control field in an Information frame are used to acknowledge recepti ons In most applications this is done by specifying the number of the next frame expected F or example if a Secondary has received two messages from the Pri mary the receive sequence number would indicate the next expected message three rather than the last message received two A detailed illustration of this process is given in Figure 4 16 Numbered Supervisory Frame Numbered Supervisory Frames are used primarily to control message flow over the data link A Numbered Supervisory Frame is identified by the first two bits of the Control field which are set to 1 and 0 respectively The supervisory functions this frame controls are e Receive Ready RR e Reject REJ e Receive Not Ready RNR e Selective Reject SREJ The third and fourth bits of the Control Field define the supervisory function to be performed
156. nce this mode supports a multiple drop bus oriented topology that offers significant benefits to the industrial user Symmetrical Link UA In this configuration each station has a Primary and a Secondary computer The Primary is responsible for enabling the corresponding Secondary to transmit and it takes coordination at the higher levels to get two stations to communicate There aretwo separate command response data streams as shown in Figure 4 13 PRIMARY Commands SECONDARY ee A B Responses a ee Commands SECONDARY PRIMARY A Responses B Figure 4 13 HDLC Symmetrical Link UA Balanced Link BA In this configuration each station has equal responsibility for mode control and error recovery over the data link This configuration uses the ABM mode of operation See Figure 4 14 f COMMANDS COMBINED COMBINED A B E RESPONSES Figure 4 14 HDLC Balanced Link BA Combined Stations SIMATIC TIWAY Systems Manual Network Architecture 4 27 4 6 HDLC Frame Structure The HDLC frame structure consists of The opening flag e Theaddress field e Thecontrol field e The data field e TheFrame Check Sequence FCS field e Theclosing flag The HDLC frame structure is shown in Figure 4 15 BITS FRAME FRAME CHECK FLAG ofi SEQUENCE FCS 01111110 Number of octets in address field m Maximum length of information field INFORMATION
157. nd increases overall system efficiency SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 31 5 7 Network Layer TheNetwork Layer allows Network User entities to exchange data reliably and in sequence across lower level services The Network Layer for TI WAY is defined as a Permanent Virtual Circuit PVC using X 25 procedures in Reference G in Appendix C The use of the Network Layer services is an option selected by the user when defining the network SeeFigure 5 18 OSI MODEL TIWAY APPLICATION WE COMMUNICATIONS MULTI TASK SESSION NEL SESSION MANAGER PRIMITIVES REDUNDANT MEDIA MEDIA rmm one PHYSICAL RS 232 C LOCAL LINE Figure 5 18 TIVAY I OSI Model Network Layer Each Secondary on TI WAY has only one PVC assigned to it The X 25 packet layer software controls the sequence and flow of data on the PVC The X 25 packet is contained within the Information field of the HDLC frame 5 32 TIWAY I Network Operation SIMATIC TIWAY Systems Manual Overview of The orderly flow of data on the TI WAY network is primarily controlled by Network Layer the Data Link layer protocols and is further enhanced by defining a Protocol window size for each PVC at the Network Layer The window size defines the maximum number of sequentially numbered data packets that a station is authorized to transmit and have outstanding at any given time With modulo 8 arithmetic a window size of 1 to 7 is possibl
158. nd of the page The lines are queued at the quarantine queue and this queue provides the entire page to the application layer Bracketing An example of bracketing can be illustrated by methods used in managing a computerized airline reservation service An airline reservations data base which contains all reservations existing at any given time must be protected while a new reservation is being made Bracketing puts a lock on the reservations data base while a new reservation is being made This prevents all other reservation terminals in the system from accessing the data base and prevents overbooking Quiescing lf a receiving computer cannot accept messages as fast as a transmitter is sending them there is a mechanism hereto slow them down Synchronizing An example of synchronization accomplished at the Session Layer could involve bank accounts where multiple copies of bank records are stored The need would be to make certain that a message is recei ved at each of the account data bases before the entire data base is updated The synchronization of data reception to data base update is accomplished here Session Identifiers are assigned at this layer as are sequence numbers to prevent messages from getting out of order Checkpointing Checkpointing is a form of error detection found in network configurations using combined stations Combined stations are those which have both a network primary and secondary at each node
159. ng a single primary station and one or more secondary stations A 10 Glossary SIMATIC TIWAY Systems Manual User application process An application process which executes functions required for information processing N User data N service data units as contained in N protocol data units i e mapped one to one blocked or segmented Virtual Circuit VC A Network facility which emulates facilities provided by a physical connection as defined in CCITT Recommendation X 25 A Virtual Circuit provides a bidirectional transparent flow controlled path between a pair of network connection endpoints SIMATIC TIWAY Systems Manual Glossary A 11 Appendix B TIWAY Primitives B 1 INTOUCION lt a eee iex uu ee be ee chee ees SOD elann TCI Organization of this Appendix Applicable Documents sera nia raien ee eec Pe D RC tb e c e Basic SUUCTUIC osos sese cs dana pec ps al aao AA AAA era td B 2 Primitive Definition 0ccccccccccc hh huhahaa nara khan rana naa Primitive Assignment Rules 2 6 0 enn Exception and Status Primitive Codes iiiissssssssss eee CONO ii ceed ei hears ae A Rete Rabe Ron la tps e Kata ee ee e ea EE Data Acquisition Primitive Codes sssssssssssss nh Primitive Procedures iure A OPA ERES DERE AAA P Tort Basic Procedure Rules susssssssssssssess es nnn Floating Point Representation seiss erra iiiia mea a kiia siaaa nn Primitive SUIMMANY 6 rt a a EE C RUP Dex E ed q
160. ng haul network a point to point transmission link or even another LAN Such an interconnection is usually accomplished with a device called a gateway which serves an an interface device between two separate digital communications environments There are at least two important considerations required when planning to use a gateway e TheLocal Area Network protocols are designed with the necessary generality to enable them to express destinations outside their own networks For example a more general address field is used and this usually leads to some overhead in the address field when it is used for purely local addresses e A data rate throughput mismatch can occur any time two networks with differing speeds are interconnected Therefore the initial network design must provide some mechanism to prevent the gateway from exhausting its buffer space Reduced cost is a major advantage of gateway interconnection because it becomes possible to connect all the computing devices on one network to another network using for example a single computer Gateway family products include gateways bridges relays adapters and converters Each differs by the amount of services and protocol translation offered SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 21 2 10 Maintenance Local Area Network maintenance as well as the monitoring of network operational status can be assisted by hardware and software distributed
161. ng use as the TIWAY network spine Belden 9271 or its equivalent should be used for the tap dropline SIMATIC TIWAY Systems Manual TIWAY Cable Installation Overview 67 6 5 Three Important Considerations Three major points to consider during the planning phase of a TI WAY network cabling system are system expansion system flexibility and noise System Expansion From the start allow for system growth This means making provisions for the attachment of additional computing devices by routing cables through all probable areas of future plant expansion System Hexibility Always make the network flexible enough to allow for rearrangement of plant equipment Noise Since network system noise is usually picked up by its interconnecting wiring steps should be taken at the onset to bypass or eliminate noise sources 6 8 TIWAY Cable Installation O verview SIMATIC TIWAY I Systems Manual 6 6 Local Line Tap Spacing On the TIWAY network as many as 254 secondaries can be attached by droplines to the main trunk cable The main trunk can be as long as 25 000 feet and each dropline can be up to 100 feet Local Line signal characteristics require that the distance between droplines on the network be calculated using the length of the last one or two droplines A maximum of two droplines may be attached at any point on the main cable The minimum distance between taps must be equal to or greater than one half the length of the last one o
162. nly sample the incoming data when the dock is present This approach ensures that any differences between internal timing of the transmitter and receiver do not affect the overall system timing In asynchronous systems the timing information is included in the serial bit stream In a character oriented protocol the start and stop bits which bracket a transmitted character are sensed by the receiver and used to resynchronize the internal clock of the receiver Internal receiver docks are designed to maintain accuracy over short periods of time corresponding to thetransmission time of one character Since each character causes resynchronization this accuracy is sufficient to maintain overall system synchronization 3 28 TIWAY Overview SIMATIC TIWAY Systems Manual In bit oriented protocols such as HDLC a message is transmitted in a continuous serial bit stream and is not segmented into characters as with a character oriented protocol Under bit oriented protocol operation synchronous systems maintain transmitter recei ver synchronization with docks provided by the modems in the same manner as with character oriented protocols Asynchronous systems however must use a different synchronization technique with bit oriented protocols since no provision is made for start and stop bits to be used in conjunction with a character This technique is implemented by designing the receiver to force resynchronization of its internal dock each time a tr
163. nt number in the excess 64 notation as defined in Appendix A Loop Set Point Theloop set point data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Output Theloop output data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A SIMATIC TIWAY Systems Manual Loop Status Theloop status data type length is 16 bits Contents of this field is defined in Figure B 5 po SIGNIFICANT BIT Figure B 5 Definition of Loop Status Data Element A Loop Mode If set to one the loop is in auto mode If set to zero the loop is in manual B Loop Cascade If set to one the loop is in closed cascade If it is set to zero the loop is in open cascade C PV High Alarm If set to one the process variable is in high alarm If set to zero the process variable is not in high alarm D PV Low Alarm If set to one the process variable is in low alarm If set to zero the process variable is not in low alarm E Error Deviation If set to one the loop is in positive error deviation If set to zero theloop is in negative error deviation F Orange Band If set to one the loop deviation is in the orange band If set to zero the loop deviation is not in the orange band G Yellow Band If set to one the loop deviation is in the yellow band If set to zero the loop deviation is not
164. number of well defined subdivisions each of which represents the intersection of the system with a layer as shown in Figure 4 4 A given layer for example Layer 3 in one computer communicates with the same layer in another computer The unique conventions used are known collectively as the Layer 3 protocol This is analogous to the use of a common language by both the writer and the reader at Layer 3 of the postal service example cited earlier No data is transferred from Layer 3 of one machine directly to Layer 3 of another however The data must travel down through the layers at the originator and up through the layers at the receiver just as the dialogue in the letter had to do Further as Layer 3 of the first computer passes data and control information to the layer below it the layer below adds control information and passes the message on just as the letter writer wrote words on a page then added an envelope an address etc n a computer network this process repeats itself until the lowest layer is reached At the lowest layer analogous to the postal truck in our real world example the actual physical connection exists to the second computer and it is at this layer that the bit transfer takes place 4 10 Network Architecture SIMATIC TIWAY Systems Manual At the receiving station the reverse process occurs Each layer strips away the control information that was added by its equivalent layer in the transmitting machine unt
165. o define one or more equivalent nonacceptable expressions so that if certain errors occur in an acceptable expression the results will be one of its equivalents and thus the error can be corrected Error Detecting Code A code in which each expression conforms to specific rules of construction so that if certain errors occur in an expression the resulting expression will not conform tothe rules of construction and thus the presence of errors is detected Synonymous with self checking code Extendable field A field whose normal length may be optionally extended e g by use of a special extension bit within the normal field Fault potential The potential differences which may be present under conditions of equipment failure or improper connection between either conductor of data transmission line and the case or local ground of a station Fault potential is measured in peak to peak volts within a specified frequency band Field A set of contiguous bits within a frame allocated to a particular function by the corresponding protocol For instance the sequence of fields within an HDLC information frame is F A C I FCS F where F Frame delimiter flag 01111110 A Address field C Control field Information field FCS Frame check sequence field Flow Control A funcion for the control of data flow within a layer or between adjacent layers Frame A series of bits considered as a unit for error and sequence checking purposes Gat
166. o peripheral resources on another computer e Exchange of data between systems e Support of more terminals in interactive applications e Greater system availability and improved performance e Conformance with applicable standards permits integration of diverse equi pment SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 25 2 14 LAN Standards Standards for LANs are important because they allow users to mix equipment they allow software to work within a standard environment and they will help promote the reduction of LAN prices through volume Several different organizations are developing standards for LANs One project in the United States is the Institute of Electrical and Electronic Engineers IEEE Project 802 which is drafting standards for CSMA token bus and token ring topologies logical link controls and high level interfaces Another group the International Standards Organization ISO has established a seven layer model for Open Systems I nterconnecti on Open Systems are those which are open to each other due totheir mutual use of applicable standards The OSI system is layered with each layer performing a specific part of the LAN s task The OSI system is also independently modifiable and is therefore adaptable to new technology and the upgrading of systems Ultimately this protects the LAN owner s investment The OSI Model s layers are listed below top down A more detailed discussion o
167. o techniques The central station can poll each of the other stations on the star to determine which one wishes to transmit or the central station must have enough capacity to communicate simultaneously with all other stations on the network SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 15 Network Topology and Media Control continued Network Access Methods As discussed above when any node on a LAN wishes to send a message it must gain access to the network transmission media Control of the media is defined as the determination of which station on a network may transmit at any given time Different control techniques indude e Token passing e Contention e Polling Token Passing A token is a unique bit pattern that continuously travels along the transmission line With it permission to use the network media is passed sequentially around the logical ring from station to station Any station receiving the token can remove it from the network send a message and then pass the token on A node has exclusive use of the channel while it has the token This mechanism for control is particularly suitable for the ring topology and the bus topology With the emergence of IEEE 802 LAN standards both the token bus and token ring topologies are expected to gain popularity for complex industrial applications Very large scaleintegration VLSI technology to assist in the media access control is required to make th
168. ocations to be monitored on a timed basis for equivalency exceeding either a minimum or maximum bound exceeding a value range or entering a value range Reporting of condition can take two forms the first is initiated in the device monitoring the data type location and the second is with the poll condition primitive Both methods of condition reporting use the poll condition primitive format Theintent of this primitive is to aid the processing load of operator panels in monitoring process variables and states for the purpose of displays and data bases System constraints do not permit the monitoring of data element locations in real time Requirements for real time monitoring should be incorporated into the executing program and appropriate action defined by the executing program Program Condition Primitive Code 53 The program condition primitive will allow specification of up to 16 different data type locations to be monitored per addressed device A control code in the request primitive defines how the data type location is to be monitored and how the condition is to be reported Additional masks may be required by the control code to specify comparison limits Request 53 CC SS TT AAAA DDDD CC SS TT AAAA DDDD lt gt lt amp gt Repeated where DDDD is defined by the control code CC and the data element type being accessed where SS is defined as the number of half second incre
169. of the communication path and control knowledge of the state of the remote communicating activity SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 11 2 5 Network Topology and Media Control A brief discussion of the different network topologies and techniques for controlling which computer uses the transmission media the mechanism for control is presented here Network topology is the pattern of interconnection used among the various computing devices of the network It is the network floorplan Designers of Local Area Networks have identified three topologies which are especially well suited to their needs They are e TheBus e TheRing e The Star NETWORK STATIONS Figure 2 4 Bus Topology 2 12 Introduction to Local Area Networks SIMATIC TIWAY Systems Manual Bus Topology Figure 2 4 illustrates a Bus Multiaccess channel topology With a bus topology each station or node is connected to a central transmission line or bus This is similar to a row of houses along a street the street is the bus the houses are the nodes and the driveways are the connections from each node on the bus Messages sent down the line do not go through but only pass by each node The bus is a passive medium with each connecting station listening for a message Any station can fail without disrupting the rest of the network because it fails in a manner representing a high impedence nontransmission state to th
170. oll per sequence Time allowed for each message can be determined by size of the message or the node s allotment of time NOTE TIWAY supports the bus topology using a primary secondary scheme that is easy to implement and has distinct advantages in networks using programmable controllers as secondaries These advantages are achieved because polling schemes in which secondary stations PCs are accessed continuously and asked for similar data types can be designed for extremely high network throughput without adding unnecessary complexity to each node SIMATIC TIWAY Systems Manual Introduction to Local Area Networks 2 17 2 6 Message Throughput Thethroughput of messages on a LAN is either deterministic or nondeterministic Determinism is the ability to predict and guarantee a given traffic load and station count as well as when a station may gain access to the media CSMA is non deterministic because it is impossible to predict when a node may be able to access a busy network Token schemes and polling networks however are deterministic by design 2 18 Introduction to Local Area Networks SIMATIC TIWAY Systems Manual 2 7 Message Routing The routing of a message is via either circuit or packet switching Circuit switching involves establishing a transmission route along a line when the access call is made This method is traditionally used with telephones but it is too slow for efficient data transmission because data travels in
171. on computing device itself Protocol transformations register control and I O transactions are managed here 2 10 Introduction to Local Area Networks SIMATIC TIWAY I Systems Manual The LAN Software Element Some advantages to this approach are The cost of hardware to attach a station to the network is often less because standardization usually lowers costs Thesignal processing load removed from the station computing device increases the computing power available on that network station It becomes possible to separate the complete networking system into distinct parts the network computing devices and the network itself Local Area Network programs consist of a set of software protocols implemented in all computing devices connected to the network These protocols are communication conventions and they allow two or more end points on a network to speak a common language The end points may be small computers programmable controllers host computers terminals and operator stations Protocol Elements Protocols consist of a set of well defined messages and the rules for their exchange They contain the following elements Addressing this includes both the destination of data messages and in some cases the name of the source Error Control this includes both the detection of errors and recovery from them Flow control the management of information flow related to buffering capacity Synchronization management
172. on multiple connections down to the Network Layer The Transport Layer in the receiving computer will then reassemble them using correlation tables In this way one complete message unit can be provided to the Session Layer of the receiving computer in the most expeditious manner possible Economics f the network connection points are expensive the Transport Layer can take multiple sessions and map them onto a single connection to the Network Layer The receiving computer will then take the incoming message train and reassign each message to the correct session connection points SIMATIC TIWAY Systems Manual Network Architecture 419 Open Systems Inter onnection OSI Model continued The Session Layer Sessions occur between specific processes which are executing in two different computers F or example one computer might be performing the following tasks simultaneously e Monitoring limit switches on a production line e Controlling the speed of a conveyer belt e Printing a status report A second computer on the same network might be executing these tasks Opening Closing a valve e Moving symbols on a controller s CRT e Monitoring an alarm system A session will occur between the two computers when the printing task in the first computer needs to know the position of the valve being controlled by the second computer In this simple example the Session Layer in the first computer initiates the session by identifying the
173. ondary there is always a delay before a reply is sent caused by the necessity for the secondary device to decode the frame and determine that all sequence counts and the CRC are correct At that timethe Secondary transmits an acknowledgment back to the Primary as shown The accepted acknowledgment to an frame is the Receiver Ready or RR The reason for the RR is that the TIWAY NIMs must pass all their requests to the Programmable Controller and the PC must act on the information and provide the desired response This takes a certain period of time In most cases it will be longer than the acceptable Response Delay period sothe RR is returned This tells the Primary that the Secondary received the message that no response is ready and totry again later At this point the Primary waits some amount of time and then transmits an RR Receiver Ready to the Secondary This indicates to the Secondary that the Primary is ready to receive information and that the Secondary may respond if the information is ready As shown in Figure 5 16 the Secondary still has not completed processing the Primary s first frame and returns an RNR Now the Primary can send down yet another Receiver Ready this time the Secondary has an answer tothe first frame and responds Thel frame returned contains the data requested by the Primary at the beginning of the process When the Primary is through with the first Secondary it moves on the Secondary 2
174. ons The TIWAY I Primary upon power up or network reset request from higher level services will perform Network Initialization Network Initialization consists of broadcasting a DI SC command to all of the secondaries to reset the secondary receive variables The Primary will then poll each of the secondaries for a response to the DISC command The Network is now in a known state of total disconnect At this point the Primary will poll each of the Secondaries with the SNRM command and will log each Secondary s response in the secondary station log maintained by the Primary After each station 1 to 254 is addressed the Supervisory Scan see Paragraph 5 6 8 will commence As with Network initialization station initialization is the responsibility of the Network Controller U pon power up it must poll each of the secondaries with a Set Normal Response Mode SNRM The Network Controller must log which of the Data Link service points respond and provide the log to higher level services NOTE If the PM550 CIM has a pending frame ready for transmission it will not discard the frame but will retain it for later transmission The send and receive variables are cleared The only way to dear this condition is to read any pending PM5501 frames Data transfer occurs when higher level services request that data be sent to a Secondary or if a Secondary has data waiting to be transmitted Data is transferred using frames with sequence numberin
175. onsible for Open Systems Interconnection 7 layer model close relationship with CCITT Contribute to ISO and also issues own standards known for last movement U S voice in ISO issues Federal intormation Processing standards for equipment soid to federal government Department of Defense need not comply Contributes to ANSI known for physical layer s RS 232 C standard Contributes to ANSI and issues own standards such as IEEE 488 bus Figure 4 1 Communications Standards Organizations 4 4 Network Architecture SIMATIC TIWAY Systems Manual Intemational Consultative Committee on Telegraphy and Telephony Intemational Standards Organization European Computer Manufacturers Association American National Standarus Institute U S National Bureau of Standards Electronic Industries Association Institute of Electrical and Electronic Engineers SIMATIC TIWAY Systems Manual This international organization is also known as the CCITT which is an acronym for its French name Comite Consultatif Internationale de Telegraphique et Telephonique CCITT is part of a U N Treaty organization known as thelnternational Telecommunicatons Union and its recommendations are law in European countries where communications are nationalized In other countries such as the United States the CCITT recommendations often become the recognized standard CCITT membership and representation is shown in Fig
176. ored TIWATI Primitives B 27 Primitive Definition continued Basic Procedure Rules B 28 TIWAY Primitives Poll Condition Primitive Code 54 Poll condition will allow a device to respond to any conditions that are enabled active as specified by the program condition Primitive Code The control code indicating the type of condition being reported the data element type location and current value will be returned The response primitive without data will be returned when there are no conditions that are enabled active Request 54 Response 54 HH CC TT AAAA DDDD CC TT AAAA DDDD Gea ea RO gt lt amp gt Repeated where CC is defined in the program condition primitive and DDDD is the current value of the indicated data element location The Primitives require that certain basic procedures be followed to insure uniformity in the expected performance The procedures fall into three classes The first is the normal operation of request and response without errors or exceptions Errors found in the interpretation or execution of a primitive form the second class of procedures and shall be referred to as exceptions Errors reported by the lower level network services eg data link timeout form the third class of errors and shall be referred to as errors Normal Procedures Thenormal operation of a Primitive is for the initiating station to form a request Primitive and address it to a device If the reque
177. ostic Codes Least Significant Bit 6 7 0 0 Problem not defined 0 1 Bad P R value returned in bits 0 2 Bad P S P S value returned in bits 0 2 Packet of incorrect length General Format Iden tifier not 0001 Data packet re sent too many times In RNR receive condi tion too long Invalid packet or packet not supported M data bit set to one 5 36 TWAY I Network Operation SIMATIC TIWAY I Systems Manual Sending a Reset Request Packet A reset request packet is sent under the following conditions e An invalid P S count is found in a data packet e An invalid P R count is found in a data packet a Receive Not Ready RNR packet or a Receive Ready RR packet e Anincorrect packet length is detected e The general format identifier is not 0001 e Multiple retransmission attempts result in a failure e Atimeout occurs after sending a reset request This applies if the secondary has the capability to time out events Ordinarily the Secondary sends a reset request packet and is waiting for a reset confirmation packet If the reset confirmation packet does not arrive within a specified time the reset request packet is sent again The reset request packet is re sent until one of the following conditions occurs A reset confirmation packet is received A reset request packet is received This will be treated as a reset confirmation since both ends are apparently attempting to reset NO
178. p reset data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Rate Theloop rate data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop High Alarm Theloop high alarm data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Low Alarm Theloop low alarm data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Process Variable Theloop process variable data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop High Process Variable Theloop high process variable data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Orange Deviation Theloop orange deviation data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Yellow Deviation Theloop yellow deviation data type length is 32 bits Contents of this field is a floating point number in the excess 64 notation as defined in Appendix A Loop Sample Rate Theloop sample rate data type length is 32 bits Contents of this field is a floating poi
179. p sequentially as it sends Information 1 frames When it finishes sending it will pass media access to the Secondary by setting the Poll bit to 1 Function of the Secondary n replying the Secondary begins its message numbering sequence with 0 and sends three messages 0 1 and 2 In each case its next expected receive from the Primary is 2 In the example shown in Figure 4 16 unknown to the Secondary the second message is destroyed through an FCS error and the Primary discards it However the Primary can t inform the Secondary of the message loss because the Secondary has not yet set the Final bit and turned the media over tothe Primary The Secondary terminates transmission and passes media access back to the Primary by setting the Final bit At this point the Primary transmits two messages and in both cases indicates that the next expected receive from the Secondary is message number one The Secondary will see this and know the Primary did not receive its last two messages At the Secondary s next response opportunity it will retransmit those two frames acknowledge the Primary s transmission and pass media access back to the Primary by setting the Final bit SIMATIC TIWAY Systems Manual Network Architecture 4 33 efesotomasyon com 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 5 10 5 11 5 12 Chapter 5 TIWAY Network Operation Intr oducti ri sec rias ia sel a ca a da ies Terminology TIVAY I
180. packet or a reset request packet is received in reply After RNR is received the receiving station can continue to receive data packets on the PVC 5 38 TWAY Network Operation SIMATIC TIWAY I Systems Manual Consecutive RNRs Consecutive RNRs received from a secondary station in a time period exceeding five seconds will be interpreted as a station failure and a reset packet will be issued The P R and P S counts are not reset when an RNR is sent or received If the station that sent the RNR continues to send data packets the P S counter is updated with each data packet sent and the P R counter indicates the next expected P S if the RNR condition is cleared without resetting Receive Not Ready Packet Format The Receive Not Ready packet format is shown in Figure 5 22 LEAST SIGNIFICANT BIT BIT POSITION LOGICAL CHANNEL NUMBER o 0m jt o t o Figure 5 22 Formatofthe Receive Not Ready Packet Receive Ready Packet RR An RR packet is used under the following conditions 1 An RR packet is sent A After an RNR packet has been sent and the RNR sender is again able to receive data packets i e the RNR condition has been cleared B When the receive window is full an RR packet can be sent to acknowledge data packets if no data packets are queued for transmission 2 AnRR packet will be received A After an RNR packet has been received and the sender of the RNR has cleared the RNR condition B To
181. porting the letter to a reader is available Paper and envelope provide the next lower layer of service to meet that requirement The message is written down enclosed in an envelope and delivered to the postal service which transports it to the mailbox of the person to whom it is addressed Again note that each lower layer has no need or desire to know the specific characteristics of the layer above it The postal truck for example cares only about transporting the letter to its proper destination Its use of language as part of the transportation system is completely independent of the writer s use of a language to write dialogue The language used by the transportation system can be a completely different protocol than the protocol used in the dialogue Consider two Englishmen living in France and corresponding with each other in English over the French postal system Fate of the Layers Astheletter progresses down through the architecture at the sending end elements are added as required to complete the path between the mind of the writer and the mind of the intended reader At the receiving end each layer is stripped away until the written words are transformed into meaning by the reader s mind Then the letter can be discarded and as far as that particular correspondence is concerned all postal system layers have ceased to exist A similar functional analysis can imagined for the telephone network and many other well organized hu
182. ports on its network side These ports can be configured for local line twisted pair operation or for RS 232 C modem operation using cards designed for that pur pose Media cards are provided by Siemens based upon the user s operational requirements Two ports on each NIM ensures redundancy on the media i e two separate twisted pairs can be installed between the network Primary and every Secondary on the system Each cable is usually installed along a different route SIMATIC TIWAY Systems Manual NETWORK PRIMARY Note T Tap Figure 3 14 TIWAY Multidrop Bus Configuration with Redundant Media Notethat the configuration shown in Figure 3 14 requires the installation of two TIWAY communication cards in the network host computer H owever only one communication card is active at any one time with the second communication card disabled Transport Layer OSI Layer 4 software services in the Primary will command which communication card and therefore which media will be used to perform TI WAY communication services NIM Redundancy Siemens Model 520 and 530 Programmable Controllers support multiple NI Ms Therefore redundancy in these PCs can be extended to include dual NIMs To support dual NIMs with full drop media redundancy four 4 separate twisted pairs would be required SIMATIC TIWAY Systems Manual TIWAY Overview 3 25 TIWAY I Topology continued Modem Multidrop Bus The TIWAY modem multidrop
183. procedures are identical to the PM550 CI M Local Line HDLC protocol with minor exceptions Both TIWAY and the Local Line use the Unbalanced Normal Response UN mode of operation However TI WAY higher level protocols differ from those used on the Local Line particularly at the Presentation Layer Layer 6 and the Application Layer Layer 7 of the OSI Model Higher Level Protocols Theterm higher level protocols is intended to distinguish protocols whose purpose is to control the computing processes involved in an application from lower level protocols which control communications processes Two computers require communications in order to send bit streams to one another but it is the higher level protocols which interpret the meaning of those bits and thus allow true utility in the system The simple reception of bits would be useless if some meaning could not be attached to them TIWAY Primitives Thehigh level protocol which is implemented across Layers 6 and 7 of the TI WAY architecture uses special coded instructions known as Primitives The Primitives are a special language which is coherent to all TI WAY I conformant Secondaries attached to the network In a command from the Primary to a Secondary using a Primitive the NIM on the Secondary translates the coded instruction into a format understandable to the Secondary computing device whether it is a Series 500 PC a PM550 or a 5TI When data is sent back to the Primar
184. quence Error Any frame with an FCS error will be discarded with the Secondary taking no action Recovery consists of a timeout in the Checkpoint cycle described above This will result in eventual retransmission of the error frame Frame Reject FRMR Error Framereject errors occur when the recei ving station receives an FCS error free frame and it contains an invalid or unimpl emented control field an invalid N R or an information field which has exceeded the maximum established storage capacity If a frame reject condition occurs in the Primary or as a response from a Secondary the Primary has the responsibility to take proper action depending on the nature of the reject If the frame reject is received from a Primary the Secondary will respond with a FRMR The command REJ should be used by the Primary to elicit a retransmission Station Disconnect Receipt of a Disconnect Command DI SC shall place the Secondary in a Logically Disconnected State LDS Then the Secondary will respond with a UA upon receipt of the DISC command The Secondary cannot accept any I UI or S frames and will respond with a DM response The Secondary station is limited to accepting a mode setting command A Primary may put the secondary in the DISC state if it is not performing satisfactorily A secondary station may become disconnected due to external conditions of secondary power loss secondary power restoration a manual reset at a secondary or when the
185. r sssussssssssssssess enn The Data Link Layer Eayer2 sess eek eda e eee a eoe d ee Network Layer OS Layer3 0 nnn Transport Layer OS Layer4 2 0 rr a A A a d A E EA The Sesion Eayer Vcc AA KE Ron d Rc aus Econ dn Presentation Layer coa e bre de heb e b I Rc en Application Layer ria CREER RE Rd EROR EN Rachid eke 4 5 High Level Data Link Control HDLC ccc cece cece eee nnn nn n e n n n n n nn HDLC Overview sssseseee ehh n Protocol Features ie la Bit SUING recess ree Fer sek ive ee hr OK n eed EAR eae DC bati ce d ModesofOperation pricini emi eug iiaa iiam dofi A nnn HDLC Station Configurations sssusa 4 6 HDLC Frame Structule iiussaashuan suus rinrin urrainn Fag Field S di rana tec tee e P CR ERE Dro E ie e eel rae tc kA Address Field ord orare a dated bale Eas pated bein xd du COMO SNA osos actore t doe ORC EUR etae ot d ate teeta re HY donde Frame Check Sequence FCS Field ssssesss n 4 7 HDLC Command Response Sequence Unbalanced Mode seeesese SIMATIC TIWAY I Systems Manual Network Architecture 4 1 4 1 Introduction Network Architecture Purpose of Section Scope of Section As discussed in previous sections a computer network is a tool enabling programs and resources residing in separate computer memories to exchange information It provides a communications service much the way an operating system provides a program execution service So
186. r two droplines Single point drops doser than one half the dropline length are considered as a double drop from the closest tap A dropline fifty feet long for example precludes the installation of the next station tap closer than 25 feet along the spine No limit is placed on the number of NIMS that can be daisy chained to form a drop line off of the main trunk as long as the resulting tap length is no greater than 100 feet Seethe examples in Figure 6 4 SIMATIC TIWAY Systems Manual TIWAY Cable Installation Overview 6 9 Local Line Tap Spacing continued EXAMPLE ONE NOT LESS THAN 30 qeria NOT LESS THAN 50 EXAMPLE TWO THIS IS CONSIDERED AS A DOUBLE DROP FROM THE CLOSEST TAP THE NEXT NEAREST TAP MUST THEN BE GREATER THAN 50 AWAY EXAMPLE THREE OVERALL DROPLINE LENGTH CAN BE UP TO 100 FEET NO LIMIT ON NUMBER OF NIMs DAISY CHAINED ON ONE DROPLINE TAP DROPLINES LESS THAN 36 IN LENGTH ARE NOT CON SIDERED IN CALCULATING DISTANCE TO NEXT TAP Figure 6 4 Network Cable Tap Configuration Examples 6 10 TIWAY I Cable Installation Overview SIMATIC TIWAY Systems Manual General Rules for Observe the following guidelines for tap line installations Tap Line Installations 1 Nomorethan two droplines from any single point on the main trunk cable can be installed 2 Thedistance between tap drop points must be greater than one half the maximum dropline length involved 3 Single point drops closer than one half the
187. raphy Affiliation representation influence CCITT International Consultative Committee on Telegraphy and Telephony international ISO International Standards Organization international ECMA European Computer Manufacturers Association Western Europe ANSI American National Standards Institute United States NBS National Bureau of Standards United States EIA Electronic Industries Association United States IEEE Institute of Electrical and Electronic Engineers international Part of International Telecommunications Union a U N treaty organization Voluntary nontreaty Computer suppliers selling inn Europe includes some U S companies Voluntary Government agency U S trade organization Professiona Society Private companies scientilic and trade associations postal telephone and telegraph administrations U S representative Is Department of State Standards bodies in participating nations U S representative is ANSI ECMA is observer Trade organization of suppliers small with about 20 members Manufacturers organizations users and communications carriers Government agencies and network users much work done by Doll Bernak amp Newman which is largely responsible tor DOD s Arpanol Manufacturers Dues paying individuals Recommendations which are law where communications in Europe are nationalized International Resp
188. rd RS 422 A Electrical characteristics of balanced voltage digital interface circuits December 1978 Reference E EIA Standard RS 423 A Electrical characteristics of unbalanced voltage digital interface circuits September 1978 Reference F PM 550 Data Exchange Marketability Specification 2457735 September 10 1980 Reference G CCITT Provisional Recommendation X 25 Interface between Data Terminal Equipment DTE and Data Circuit Terminating Equipment DCE for Terminals Operating in the Packet Mode on Public Data Networks Geneva 1977 Reference J Siemens Program Master 550 Computer Reference K EIA Standard RS 232 C I nterface between Data Terminal Equipment and Data Communication Equipment Employing Serial Binary Data Interchange August 1969 Reference L 1SO IS 2110 1972 E Data communication Data terminal and data communication equipment Interchange circuits Assignment of connector pin numbers Reference M Siemens Series 500 Communiction Task Code Capability Specification Document 2457751 Current Revision Reference N Siemens TIWAY Protocol Specification Document 2457778 Current Revision Reference O Siemens TIWAY Primitive Specification Document 2457787 SIMATIC TIWAY I Systems Manual Referenced Documents C 1 Customer Response We would like to know what you think about our user manuals so that we can serve you better How would you rate the quality of our m
189. re DDDD is the contents indicated by AAAA Remove Primitive Code 41 Remove will delete a specified number of instruction execution memory locations from a specified starting location Certain device types will perform additional operations to dean up the end of memory Exact rules for clean up are defined in each unique device type Request 41 AAAA NNNN Response 41HH Insert Primitive Code 42 Insert will insert data elements into contiguous memory locations from a specified starting location Certain device types will perform additional operations to clean up the end of memory Exact rules for clean up are defined in each unique device type Request 42 AAAA DDDD DDDD lt gt lt gt Repeated where DDDD is defined by the device type being accessed Response 42 HH SIMATIC TIWAY Systems Manual Function Primitive Thefunction primitives are grouped by their intent in separate sections Codes Thefunction groups indude data acquisition and report by condition The Function Primitive Codes are grouped by their intent in separate sections The function groups include data acquisition and report by condition Data Acquisition The data acquisition Primitives allow predefined specific random blocks of Primitive Codes different data type element locations to be accessed with a simple primitive without specifying the blocks in each transaction The define primitive allows the specification of the random blocks
190. rk Primary 3 38 TIWAY Overview For full conformance any TIWAY host computer should provide these minimum services e Access to all TIWAY Secondary computing devices through high level Primitives e Network performance information to allow the user to evaluate network throughput and the status of TI WAY devices e Allow easy addition and subtraction of network secondaries e Provide the ability to select an alternate redundant set of network services e Enable data transfer between network computing devices by some method other than direct Input Output coupling User access to network services on TIWAY should utilize the same procedures regardless of host computer type The Siemens 5100 computer provides its user with a networking tool which allows him to design his own operator interface using a built in real time multi tasking operating system and a real time BASIC programming language This computer has been used with many Siemens Programmable Controllers for both PC control and data acquisition It is designed for single point of control for all plant processes Siemens 5100 Features The5100 contains 128 K bytes of dynamic RAM and its memory is expandable to one megabyte There are 8 auxiliary RS 232 C interface ports and 2 network ports for network access Some additional features are e Standard IEEE 796 bus architecture e 1500 Vrms of electrical isolation on the network to prevent ground loops
191. rm should be found in the Glossary at the end of the manual SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 3 5 2 TIWAY I Relationship to the OSI Model Figure 5 1 illustrates the relationship of each layer of the TI WAY architecture to the corresponding layers of the OSI Model discussed in Chapter 4 of this manual The remainder of this section presents a functional discussion of the TIWAY architecture For a description of the OSI Model refer to Chapter 4 OSi MODEL APPLICATION PRESENTATION SESSION TRANSPORT NETWORK DATA LINK PHYSICAL TIWAY COMMUNICATION PRIMITIVES MULTI TASK SESSION MANAGER REDUNDANT MEDIA SELECTION X 25 PVC USER OPTION RS 232 C LOCAL LINE Figure 5 1 TIWAY I OSI Model Relationships 5 4 TIWAY I Network Operation SIMATIC TIWAY Systems Manual 5 3 Media Access Control Protocol Overview TI WAY is a hosted system The Network Controller Primary has all the responsibility for network management This includes Flow Control e Network Initialization e Error Recovery e Granting Media Access The Network Controller Primary provides management through a polling scheme and the use of the P F bit Secondaries in the Normal Unbalanced Link configuration are not allowed to transmit unless given explicit access to the media The polling scheme is a time division process with data priority SIMATIC TIWAY Systems Manual TIWAY Network Oper
192. rmance criteria in the form of an actual performance example is given This section should be studied and understood before going on to Chapter 4 No attempt will be made in this section to present a detailed theory of operation of TI WAY The intent here is to provide a general overview only For an in depth analysis of TI WAY the reader should consult Chapter 5 Certain terms used throughout this manual may be unfamiliar to those who are not conversant in data communications n some instances the definition of a new term is provided within the text but in cases where that would interrupt the flow of the material being presented the unfamiliar term should be found in the Glossary at the end of the manual This manual assumes that the user is familiar with basic computer networking theory and makes no attempt to provide a comprehensive overview of that subject SIMATIC TIWAY I Systems Manual Factors Promoting Some of the factors pushing distributed control are the reduction in cost Distributed Control and size of microprocessors the improvement in speed and reliability of data communications and the increasing sophistication of the software which enables multiple computing devices to function harmoniously in a network A typical partitioning of control in a modern factory is shown in Figure 3 1 ACCOUNTING e INVENTORY CONTROL e PROCESS MONITORING NETWORK amp TUNING CONTROLLER e STATISTICS COLLECTION INDEPENDENT PROCE
193. rovided HDLC is closely related to ANSI s ADCCP and IBM s SDLC It is a bit oriented protocol as opposed to a character oriented protocol This overview of HDLC will cover e Protocol features e Frame structure e Command Response sequence Unbalanced Mode HDLC is a standard which defines the frame structure and procedures for information exchange between Data Terminal Equipment DTE It isa bit oriented protocol which means that its data frames can contain an arbitrary number of bits Character oriented systems use integral multiples of a specific character size to delimit frames In HDLC the length of the data field can vary and the total message length can therefore vary In TI WAY I the information field I field can be up to 282 bytes long All bit oriented protocols which include HDLC SDLC and ADCCP usethe standard frame structure shown in Figure 4 15 This structure includes a special bit pattern to signal both the beginning and the end of an HDLC frame This pattern is always 01111110 and it cannot occur anywhere else except at the beginning or the end of a message To ensure the uniqueness of the frame delimiting flags a technique known as bit stuffing is used Whenever a sending computer sees five consequtive ones in the data bit stream of an outgoing message it automatically inserts a O bit A receiving device which sees the five incoming 1 bits automatically deletes the 0 bit In this way only the opening or
194. rted the PM550 and 990 computer products since 1979 The enhancements to the Local Line include extended geographic coverage increased baud rates for information throughput and a common interface which permits communications with any of the above mentioned Programmable Controllers TIWAY Control Mechanisms TIWAY is a hosted network a Primary host computer controls up to 254 separate Secondaries providing a central collection point for information With appropriate host software a TI WAY operator can program monitor and control any PC on his network from a single location See Figure 3 2 TIWAY uses the industry standard High Level Data Link HDLC protocol and conforms to the CCITT X 25 standard for packet switching SIMATIC TIWAY I Systems Manual PRIMARY COLOR TERMINAL CONTROL UNIT PROCESSOR uf SECONDARIES Figure 3 2 TMWAY I TIWAY I Architecture Thenetwork is a multidrop bus or star architecture defined in Chapter 2 using as a communications medium a local line twisted pair cable and or modem attachment facilities TIWAY Local Line geographic coverage can be as great as 25 000 feet without modems depending on the type of communications cable used the number of Programmable Controllers on the network the communication speeds desired and the station node placement Modem geographic coverage and communication speeds are dependent on the operating ch
195. s and error detecting methods e Error correcting methods use forward control where enough redundant data is included with the basic message to enable not only error detection but a determination of the correct message e Error detecting methods use redundant information to enable a receiver to detect an error whereupon correction is made by message retransmission Redundancy ensures that the failure of a single communications component on a LAN does not isolate any station on the network There are two kinds of redundancy related to network hardware e Media redundancy e Interface redundancy Media Redundancy Redundant media usually consist of installing more than one physical medium between network computing devices Some interface modules such as TIWAY Network Interface Modules NIMs are specifically designed to accommodate redundant transmission media Interface Redundancy Interface Redundancy typically involves the use of more than one interface module on each separate computer on the network A LAN with redundant interface capacity can also be designed with redundant media This usually requires dual transmission lines for each interface module TI WAY also supports this configuration 2 20 Introduction to Local Area Networks SIMATIC TIWAY Systems Manual 2 9 Gateways One important service a Local Area Network can provideis an interconnection capability to another digital communications system such as a lo
196. s are summarized in Table 5 5 Table 5 5 Summary of Field Symbols symbol AAAA Data Element Location DDDD Basic Data Unit LEEL Length PP Primitive Code 5 56 TIWAY Network Operation SIMATIC TIWAY Systems Manual TIVAY I Primitive The subset of TI WAY Primitive Codes selected for original release are Code Subset given to Table 5 6 below Future additions to this subset will be announced as they implemented Note that each of the following Primitive Codes fit into the general categories listed in the Logical Primitive Code Assignment Table Table 5 6 Series 500 NIM Primitive Code Subset Machine type configuration 04 Primitive format configuration 10 Change state 20 Read block single contiguous block 30 Write block single contiguous block 50 Define blocks up to 16 separate blocks Gather bcc as defined SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 57 efesotomasyon com Chapter TWAY Cable Installation Overview 6 1 Introduction cccccccoccrr ra a aa ra a rn na 6 2 Scope of Section occccccccc nhanh naar aaa aa aan an 6 3 TIVAY I Unit Loading Versus Cable Distance s seen n n n n n n n n n n n nn 6 4 TIVAY Hardware Media Components enne nnn rl ara trees ito dea Twisted PairCabling vertida ds 6 5 Three Important Considerations cccccccccccrcc nnne System BHaNJO Ms siaaa rE ka ka a eese nn System FeXb ily 2 cien cte eee tete m e ath deb ek
197. s required to prevent contention from all other secondary modem carriers when a particular secondary is trying to transmit to the primary Control of the secondary modem carrier should be implemented with the REQUEST TO SEND CLEAR TO SEND handshake that is required when using half duplex modems ONE CHANNEL TRANSMIT FREQUENCY 1 FULL DUPLEX TRANSMIT FREQUENCY 2 ONE LINE HALF DUPLEX ONE DIRECTION AT A TIME Figure 38 TIVWAY Modem Types Network Control The function of the Network Control Module NCM whether it is a card Module blackbox or computer is to act as a network Primary All commands are initiated by one Primary This is referred to as the Normal Response M ode NRM Secondaries can send data only to the Primary station Each Secondary is polled on a time selected basis and must wait until it is polled before transmitting a response SIMATIC TIWAY I Systems Manual TIWAY Overview 3 17 3 8 TWAYIasa Hosted Network OSI Model Layer 6 7 interface Layer 5 6 interface Layer 4 5 interface Layer 3 4 interface Layer 2 3 interface Layer 1 2 interface 3 18 TIWAY Overview Thefollowing paragraphs describe the basic operation of the TI WAY I hardware and software components functioning as a unit The software makes the system operation largely user transparent An overview of the basic operation is given here for a more detailed discussion see Chapters 4
198. scarded An exception Primitive will be returned indicating the condition Error Procedures The error procedure is used when communication protocol services report that a reliable data link can not be established or has been lost with the addressed device E xact error definitions are dependent on the protocols employed The errors will fall into two classes the first is due to the network being incapable of transferring information the second is due to the addressed device failing to respond reliably An attempt counter should be maintained and the primitive aborted if after a predefined number of attempt failures The error condition is flagged and further operations are dependent on supervisory control functions SIMATIC TIWAY Systems Manual TIWATI Primitives B 29 Primitive Definition continued Hoating Point Floating point numbers are represented by two 16 bit words The number Representation consists of a normalized hexadecimal fraction a hexadecimal exponent and a sign bit as shown in Figure B 6 The fractional component of the number is normalized between 0 and 1 without leading zeros between the radix point and the first significant digit of the fraction MSB OF NUMBER LSB OF NUMBER Figure B 6 Hoating Point Number Where MNEM of bits Definition S 1 Sign bit EXP 7 Exponent MSB 8 Most significant bits of the number LSB 16 Least significant bits of the number The exponent component of the number is biased by 40 exc
199. sed The last eight bits form the preset step to be accessed within the indicated drum number instruction data type These are represented in Figure B 3 DRUM NUMBER PRESET STEP Figure B 3 DCP Location Format Input Output Location Descriptor Format The length of discrete or word input output data element type location Descriptor Field is Sixteen bits Loops Location Descriptor Format Thelength of loop data element type location Descriptor Field is eight bits Number of Locations to Access NNNN Thelength of the Number of Locations to Access Descriptor Field is either eight or Sixteen bits dependant upon the Primitive definition in Section 4 A value of one shall be interpreted as one location to be accessed The number of locations descriptor shall be denoted NN for an eight bit field and NNNN for a sixteen bit field in this Appendix The total number of bytes requested should not exceed the maxi mum allowed for that device type BASIC DATA UNIT DDDD Thedefinition of the basic Data Unit Field is dependent upon the data element type specified in the Descriptor Field and the Primitive format definition found in Section 4 The following sections define the basic data unit format for each data element type The basic data unit shall be denoted DDDD in this Appendix Instruction Execution The minimum instruction execution data type length is 16 bits with 16 bits as a minimum field increment Native machine language instructions are
200. serted here In the Secondary s response the Secondary s own address is given back since there is only one Primary on the network to receive the transmission This tells the Primary the message source The Control Field is an eight bit field used for acknowledgments message sequence numbers and for defining frame types as discussed below There are three kinds of HDLC Frames e Information e Numbered Supervisory e Unnumbered Supervisory Information Frame Information frames are those which carry data in the Information field However the frame type is defined in the Control field Ifthe HDLC frameis an Information frame the first bit of the Control Field is set to O and the next three bits indicate the send sequence number For example in the case of the first information frame sent the first four bits of the control field will be 0000 The second information frame will result in 0001 and so on Since only bits 2 3 and 4 of the control field are used in the count the highest number the first four bits of and information frame can indicate is 0111 or 7 The fifth bit in the control field is the Poll Final bit If the message is from the Primary to the Secondary the fifth bit is the Poll bit if the message is from the Secondary to the Primary it is theFinal bit When a Primary wants to transmit data to a specific Secondary it sends the Secondary a message with the Poll bit set to 1 The Secondary then responds with the Fi
201. signments are done by the host The LCI assignment is formatted as described below SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 33 Network Layer continued X 25 Packet Description Refer to Figure 5 19 for the following discussion The X 25 packet is defined as Byte 3 Ifield descriptor This field is included to insure the integrity of this format in the event that any other future system parameters must be sent using the UI command 4 0001 is the General Format Identifier and is included to fill the left half of byte 4 GGGG is the Logical Channel Group number assigned to the secondary 5 CCCCCCCC is the Logical Channel Number assigned to the Secondary It is usually the Data Link Service Address 00000000 0001GGGG CCCCCCCC FCS FLG X 25 PACKET Figure 5 19 The X 25 Packet System Operation Upon receiving this message the Secondary Data Link control invokes Network UI processor and responds to the Primary station with the HDLC UA The Secondary UI processor then assigns GGGG CCCC CCCC as its LCI The LCI will bein every packet sent on the PVC The TIWAY Secondary when the X 25 option is selected will not accept or transmit data packets or flow control packets until the LCI is assigned The Secondary has the responsibility of retaining the LCI for all future transactions 5 34 TIWAY Network Operation SIMATIC TIWAY Systems Manual Flow Control Flow of data on the PVC is controlled
202. sion layer allows different application programs in the network Primary to communicate with a Secondary on the network It is a host resident program defined by the user SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 45 5 10 TIMAY I Presentation and Application Layers In a TIWAY network utilizing all the different types of Programmable Controllers 520 530 PM 550 and 5TI PCs the Presentation and Application Layers function together to give the user device transparency between all PC types Simply stated this means that all TI WAY conformant devices attached to the network appear the same to the network Primary This vastly simplifies the software required in the Primary and enables large blocks of information to be moved efficiently around the network This device transparency is made possible by the implementation of special coded instructions known as Primitives The Primitives are implemented at the Presentation and Application layers See Figure 5 25 OSI MODEL TIWAY I 7 APPLICATION COMMUNICATION PRIMITIVES PRESENTATION ae MULTI TASK SESSION SESSION MANAGER REDUNDANT TRANSPORT MEDIA SELECTION X 25 PVC NETWORK USER OPTION NM PHYSICAL RS 232 C LOCAL LINE Figure 5 25 TIWAY I OSI Model Relationships Layers 6 and 7 5 46 IIWAY Network Operation SIMATIC TIWAY I Systems Manual Special Considerations Task Codes Effective application of the information contained in the
203. sponse transmissions exists with the P F bit If the UP has the P bit set to 1 the secondary response must havethe F bit set to 1 Response frames may contain N S and N R numbers if required by the particular response C U NOTE The PM550 CIM does not support the U P command FRMR Frame Reject Used by the secondary to report that one of the following conditions resulted from the receipt of a frame Primary and secondary message sequence numbers are not affected by transmission of this response The error is not recoverable by the retransmission of the identical frame NOTE In PM550 documentation FRMR is referred to as CMDR for Command Reject FMFR conditions A frame contained an invalid or not implemented command An I frame was received with an information field which exceeded the size of the buffer space available An invalid message count N R was received from the primary Received a command with an field where an field is not valid for the command type 5 18 TIWAY I Network Operation SIMATIC TIWAY I Systems Manual A three byte field is required with the FRMR response and its format is defi ned as follows BIT POSITION BYTE 0 BIT BYTE 1 BIT BYTE 2 BIT FIRST BIT TRANSMITTED LEAST SIGNIFICANT BIT Figure 5 11 FRMR Response Field Format FRMR I Field Byte Definitions e Byte0 The rejected command is returned in this byte e Bytel This byte contains the current sen
204. sponse from a secondary when it is set to one The secondary will respond with the F bit set to one to indicate the end of transmission U nbalanced configurations may only have one outstanding command frame with the P bit set to one at any given time Before the primary can send another command frame with the P bit set to one it must receive a response frame with the F bit set to one The only exception to this is if the secondary does not respond to the primary poll within the system ti meout limits The information format is used to convey information or data to from primary and to from secondary The fields N S and N R are the message sequence numbers for messages sent N S and messages received N R SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 15 Data Link Media Access Control Layer continued Frame Sequencing n TI WAY I frame sequencing is used and information transfer is based on the form of a frame Each frame is sequenced to check against any type of duplication or error that might occur from retransmission This capacity is implemented in the form of a sequence number that is applied to each frame This is true regardless of whether the frame is transmitted from the Primary or the Secondary Thetransmitting computing device typically sequences and counts its frames in the N S send or transmit sequence count A receiving station then compares what it thinks the frame count ought to be agains
205. ss reserved as a null address and address 255 reserved as a broadcast address NOTE PM550 CIM secondary stations have a maximum address of 32 O is a valid address for the PM550 CIM but is not a valid address for TI WAY I NIMs TM 990 secondary stations have a maximum address capability of 63 with a maximum of 32 active stations at any one time Series 500 products have a maximum address of 254 Control Field The control field is used to convey commands from primary to secondary and responses from secondary to primary These commands are designed to control the flow of data between TIWAY stations See Figure 5 9 BIT 0 8 16 24 Figure 5 9 TIWAY I HDLC Frame Control Field 5 14 TWAY I Network Operation SIMATIC TIWAY Systems Manual Control Field Format The control field is formatted differently for the different types of command response functions provided The formats for this field are as follows NOTE This sample format is reversed from that described in Reference B in Appendix C to show the way the bit pattern would reside in the 990 minicomputer BIT POSITION 0 4 5 6 7 INFORMATION NS ES vemm om ffs ep FIRST BIT TRANSMITTED LEAST SIGNIFICANT BIT Figure 5 10 Control Field Format Control Field Poll Final Bit TheP F Poll Final bit is designated P when used with a command frame and is designated F when used with a response frame The P bit is used by the primary to solicit a re
206. st Primitive contains the allowable data element types data clement location ranges and Primitives for that specific device type addressed then the device addressed will return a response Primitive of the proper format The amount of time between a request and its associated response is dependent upon the network traffic load the network state the network poll strategy the response times of the specific device addressed and the primitive Because of the large number of factors involved no attempt is made to quantify a primitive response time It is expected that no response after 5 seconds should be considered an error although certain Primitives and network states could exceed this figure It is expected that other services of the employed protocols will handle flow control problems SIMATIC TIWAY Systems Manual Exception Procedures The exception procedure is used when the addressed device either finds fault with a primitive format data element types data element location ranges or detects a fault in executing a primitive The exception reason is returned with the exception primitive and the procedure taken is dependent on the Primitive used There aretwo dasses of procedures used for exception handling those which are associated with reading data elements and those which are associated with writing data elements An attempt counter should be maintained and the primitive aborted if after a predefined number of attempt failures The ex
207. t the recei ved frame count and then sequences its own receiver count N R incrementing one step every time it receives a new frame f the count of the received sequence count does not match the count of the send sequence from the transmitter then an error has occurred and the message must be retransmitted Arriving frames with the wrong sequence count or which are out of sequence or are duplicates are rejected When a discrepancy in the sequence count between the transmitter and recei ver is detected what typically happens is that the detecting device requests that the sending device go back a specified number of frames as indicated by the receipt of the last reliable frame and start retransmitting This ensures that any particular frame will not be lost and that the sending and receiving devices will manage the link Numbered Supervisory Format TheNumbered Supervisory format is used to perform link supervisory control functions such as acknowledge frames request retransmission of an frame etc Commands Responses of this type do not contain an I field but do contain an N R count which indicates the sequence number of the next expected frame to be received Unnumbered Control Format TheUnnumbered Control format is used to extend the number of line control functions Frames transmitted using this format do not increment the sequence counts at either the transmitting or receiving station Commands responses of this type may or
208. t in serial transmission and n bits in parallel transmission Plant environment The ambient atmosphere conditions together with electrical electromagnetic and radiation interference within industrial process plants Polling The process whereby data stations are invited one at a time to transmit cf Selecting Presentation image The data structure and actions of a presentation entity observable via a session connection Presentation Layer Layer 6 of the OSI architecture The purpose of this layer is to represent information to communicating application entities in a way that preserves meaning while resolving syntax differences The Presentation layer provides the services of data transformation and formatting syntax selection and presentation connections to the Application layer Primary station The master station in HDLC and ADCCP unbalanced configurations N Protocol A se of rules semantic and syntactic which determine the communication behavior of N entities in performance of N functions N Protocol control i nformation nformation exchanged between two N entities using an N 1 connection to coordinate their joint operation N Protocol data unit A unit of data specified in the N protocol which consists of N protocol control i nformation and possibly N user data N Protocol identifier An identifier used between correspondent N entities to select a specific N protocol to be used on a particular
209. ted blocks may not exceed 128 Following the mask is the data units associated with the write function The write funcion is to be performed before the gather operation A write and gather Primitive may be used with zero write data units The response Primitive will return the data associated with the requested blocks starting with the lowest number block increasing to the highest number block A data block separator is not provided in the response Primitive The use of the write field is optional and will not generate an error if no data is included Request 52 EEEEEEEE TT AAAA DDDD DDDD gt lt gt Repeated where EEEE is 32 bits defined as LL E BLOCK NUMBER 20 HEX BLOCK NUMBER 1 Response 52 HH EEEEEEEE DDDD DDDD DDDD DDDD olaaa TR RE gt Repeated where EEEEEEEE is mask as defined by the request primitive and DDDD is defined by the data type being accessed The order of return of the blocks is from the lowest numbered block to the highest For example if block numbers 2 4 and A were requested in the request primitive the first data block in the response primitive is data associated with block number 2 the next data block associated with block number 4 and so on SIMATIC TIWAY Systems Manual TIWATI Primitives B 25 Primitive Definition continued B 26 TIWAY Primitives Report By Condition Primitive Codes The report by condition primitives allow predefined data element type l
210. that represents an intelligible symbol Circuit switching A process that on demand connects two or more data terminal equipments and permits the exclusive use of a data circuit between them until the connection is released N Connection An association established between two or more N 1 entities defined by their n service access poi nt addresses for conveying N service data units Contention A condition arising when two or more data stations attempt to transmit at the same time over a shared channel or when two data stations attempt to transmit at the same time in two way alternate communication Correspondent entity A peer entity at the other end of a connection from the entity which is the point of reference Data Circuit Terminating equipment DCE The functional unit of a data station that establishes maintains and releases a physical connection and provides those functions necessary for signal conversion between the data terminal equipment and the transmission line Datagram DG A network facility providing for the transmission of a single Network service data unit to a specified network connection endpoint without the need for a call to be established A 2 Glossary SIMATIC TIWAY I Systems Manual Data Highway The means of transmitting frames between stations interconnected by a data transmission line A data highway consists of a data circuit and the Physical and Data Link layers of the stations connected to the
211. the TI WAY bus can be broken down into of TIWAY e Local Line Multidrop Bus e Redundant Local Line Multidrop Bus e Modem Multidrop Bus e Redundant Modem Multidrop Bus Local Line Multidrop Bus The local line multidrop bus for TI WAY is shown in Figure 3 13 below This configuration features a single transmission line NETWORK PRIMARY MAIN TRUNK NETWORK CABLES f ES EM 530 PM550 520 5TI PC PC PC PC Figure 3 13 TIWAY I Local Line Multidrop Bus Configuration Note T Tap SIMATIC TIWAY Systems Manual TIWAY Overview 3 23 TIWAY I Topology continued 3 24 TIWAY Overview The bus configuration shown above consists of one or more NIMs attached by drop cables to a main trunk Thetrunk should be constructed of high quality cable such as Belden 9860 or equivalent with drop line cables of Belden 9271 or equivalent H owever the cable used for the different segments are not restricted to the above mentioned cable types Restrictions placed on the main trunk cable and the drop cables are included in Chapter of this manual A single NIM physical configuration not shown would appear as a point to point network but would function as a multidrop network with a single Secondary station address in the host software Media redundant Local Line Multidrop Bus A media redundant Local Line configuration is shown in Figure 3 14 Redundant media is possible in TI WAY because each TI WAY NIM has two signal
212. the same manner A primary can access for example mage Register memory in a NIM equipped 520 530 5TI and PM550 PC with exactly the same command The Primitives have been implemented to remove the differences between the PCs sothat applications programmers at the Primary level won t have to sort out their secondary devices by type and then write routines in their software to fit each different type The primitives also allow more efficient data access by adding powerful options to the data transfer Data types lengths of data types and data addresses which go beyond those provided by the Task Codes discussed above are provided in the standard programming peripheral For example in any one of the PCs the VPU communicates using Task Codes The Primitives take that a step higher to increase the throughput and the data flexibility of the data transfer Some of the benefits of the Primitives are e A reduction of the network host software that is needed to acquire data from the secondaries e Theelimination of the different types of software that are needed to handle different types of secondaries in a unique manner e More efficient use of the available bandwidth by increasing the amount of data that is availablein a single message For example with a single peripheral Task Code a user might be able to access no more than 15 words of data With some Primitives up to 128 words can be accessed e A reduction in total system loading Th
213. through the use of e The packet send variable P S e Thepack receive variable P R e The window size The send receive variables after network service initialization or packet reset will be set to zero The P S is used to indicate the current sequence number of the data packet The P R is used toindicate the next expected send variable and to acknowledge the recei pt of the previous data packet X 25 Packet Structures Thefollowing paragraphs describe the packet layer interface structures between a Primary and a Secondary Each packet transferred over the Data Link is contained in an HDLC numbered information 1 field Only one 1 packet is contained in each field and only the data transfer packet is accompanied by user data The length field follows the packet header Reset Request Packet A reset request packet resets the send and receive variables to zero with packets pending transmission returned to higher level services and notified of the reset request The format of the Reset Request Packet is shown in Figure 5 20 LEAST SIGNIFICANT BIT BIT POS 4 5 6 7 LOGICAL CHANNEL NUMBER 0 0 0 1 1 0 1 1 0 0 0 0 0 0 0 0 DIAGNOSTIC CODE LCG LCN LCI Figure 5 20 Format of the Request Reset Pac ket SIMATIC TIWAY Systems Manual TIWAY Network Operation 5 35 Network Layer continued Diagnostic Codes Byte 4 Defined The diagnostic codes Byte 4 in Figure 5 20 are defined in Table 5 3 Table 5 3 Diagn
214. throughout the network Actual monitoring is usually accomplished from one control center By prudent use of automatic checkout techniques such as self diagnostics and remote sensing of component failure system failures and degradations can be detected early Local Area Networks generally feature high connectivity the ability of all stations on the network to exchange messages and good reliability availability and maintainability 2 22 Introduction to Local Area Networks SIMATIC TIWAY I Systems Manual 2 11 LAN Applications Resource Sharing One of the primary uses of a LAN is resource sharing The goal hereis to lower the system cost by sharing expensive and sometimes under used resources such as disks printers remote communications and other CPUs In addition to lower cost shared resources allow greater equipment availability because a user is not tied to one physical resource For example a user may have access to several types of printers on the network An extension of this concept is to group peripherals of the same type together under the management of servers For example a print server s job is to manage print requests and route them to the printers attached to it Disk file and communications servers are also commonly used Networked Programmable Controllers which provide data acquisition and control of factory floor processes can improve plant efficiency cut waste improve yields optimize schedules reduced down
215. tion Control Procedures ANSI X3 66 Address Service access poi nt address Allocation Mechanism The means by which a shared resource is assigned to the various entities which are potentially able to use it For example the use of shared memory in a computer Application Layer The highest layer in the OSI Architecture Protocols of this layer directly serve the end user by providing the distributed information service appropriate to an application and to management of the service and of the application Application Process An application entity which represents a procedure in execution the ultimate source and sink for data exchanged between stations For example if a printing task executing in one computer needs data located in a second computer the application program in the first computer is the sink the application program in the second computer the source Architecture System A statement of the services to be performed at each layer of the system and the protocols governing the co operation of peer entities at each layer Asynchronous transmission A mode of data transmission such that the time of occurrence of the start of each character or block of characters is arbitrary once started the time of occurrence of each signal representing a bit within the character or block has the same relationship to significant instants of a fixed ti me frame Availability The ratio expressed as percent of the time a device or system is
216. tional Status Bit encoding 00 Operational 01 Channel A is not functional 02 Channel B is not functional Fatal and non fatal errors are defined by each unique device Not all device types support loops Loop Input Output modules not induded Configuration Primitive Code O3 Therudimentary physical and logical configuration of the device addressed is reported by this Primitive Specific configurations such as mix of inputs and outputs special function location and types communication port configurations and other specific device type parameters can be obtained using the native primitive SIMATIC TIWAY Systems Manual Request 03 Response 03 HH DDDD EEEE FFFF GGGGIIII JJ JJ where Symbol Value Device Definition DDDD Device type 00 5TI 10 510 20 520 30 530 40 540 50 550 60 560 70 570 80 PM550 81 PM551 EEEE hex Instruction data type memory size FFFF hex Variable data type memory size GGGG hex Constant data type memory size Hl hex Local input output memory size 333 hex Global input output memory size Format Configuration Primitive Code 04 ThePrimitive length supported by the attached device is reported by the Primitive The length is returned is in number of bytes Request 04 Response 04 NNNN MM where NNNN is the Primitive length supported in bytes and MM isthe number of blocks supported in the data acquisition Primitive SIMATIC TIWAY I Systems Manual TWATI Primitives B 17
217. to ensure uniformity in performance the Primitives require that certain basic procedures be followed These procedures fall into three dasses 1 Normal operation of request and response without errors or exceptions 2 Errors found in the interpretation or execution of a Primitive 3 Errors reported by the lower level network services for example data link timeout Normal Operation The normal operation of a Primitiveis for the initiating Primary station to form a Request Primitive and address it to a Secondary on the network If the request Primitive contains the allowable data element types data element location ranges and the correct Primitive for the specific device type addressed then the device addressed will return a response Primitive of the proper format The amount of elapsed time between a request and its associated response is dependent upon e Thenetwork traffic load e Thenetwork poll strategy e Theresponsetime of the specific device address e The Primitive itself Dueto the large number of factors involved no attempt will be made here to define any specific Primitive response time In general however no response to a Primitive after 5 seconds should be considered an error Features of the lower level protocols in TIWAY should handle any flow control problems of this nature Exception An exception procedure is used when the addressed device finds fault with Procedures 1 A Primitive format 2 A data ele
218. uipment defined as any component which because of its design characteristics cannot operate at the TI WAY enhanced performance levels utilizing Primitives SIMATIC TIWAY Systems Manual TIWAY Overview 3 33 3 14 TWAY I Conformant Products 3 34 TIWAY Overview TI WAY conformant products consist of 520 530 Programmable Controllers with the TI WAY Network Interface Module NIM installed A computer such as the 5100 serving as the TI WAY I Primary utilizing the Network Control Module NCM TI WAY communication card PM550 Programmable Controllers with the TI WAY Network Interface Module NIM installed 5TI Series 102 103 Programmable Controllers with the TI WAY I Network Interface Module NIM installed Transmission M edia constructed of high quality cable capable of supporting data rates up to 115 2 K bps Software residing in the Network Primary which supports all TI WAY enhancements RS 232 C compatible modems which will support data transfer rates up to 115 Kbps SIMATIC TIWAY Systems Manual 3 15 TMAYI Compatible Products Some examples of existing TI WAY compatible products which attach to a reduced performance TI WAY network are e PM550 CIM e TM990 308 Industrial Communications M odule ICM e Model 990 Computer DX10 HDLC Communications Package e Transmission Media which will support data communications rates up to 9 6 Kbps e Modems which will support data communications rat
219. um for transferring signals over a distance Deblocking A function of an N entity to identify multiple N service data units which are contained in one N protocol data unit the reverse of the blocking function Decentralized connection A multi endpoint connection in which data sent by an entity associated with a connection endpoint is received by all other entities Democratic system A distributed system which attempts to maintain equal access times for all stations Demultiplexing A function of an N entity to identify multiple N connections which are supported by one N 1 connection the reverse of multiplexing Distributed application A function which is implemented using cooperating application processes characterized by multiple procedures which may be executed in different systems Distributed media access control A data link function in which the responsibility for media access control is distributed among more than one station SIMATIC TIWAY Systems Manual Glossary A 3 Drop Line A flexible coaxial cable which usually drops from an overhead tap in the coaxial network The end of the drop line has the network outlet connector which is used to couple an external device Error control procedure That part of a protocol controlling the detection and possibly the correction of transmission errors Error Correcting Code A code in which each acceptable expression conforms to specific rules of construction that als
220. unications media It also controls when a given NIM may transmit The TI WAY communication card operates as an HDLC Primary in the Unbalanced Normal Response mode and there is one active communication card or NCM function on every TIWAY installation The TIWAY communication card performs signal transformations which convert input signals from the network primary master to levels that are satisfactory for transmission over an RS 232 C interface or a Local Line twisted pair The type of transmission media used RS 232 C or Local Line depends upon the network configuration SIMATIC TIWAY Systems Manual TIWAY Overview 3 7 Network Control Module NC M The TIVAY I Primary continued 3 8 TIWAY Overview When the TI WAY network Primary host computer wants to communicate with a network secondary it sends its message to the communication card This message will consist of data or instructions for the network Secondary as well as the Secondary s address The main function is to encapsulate the message in an HDLC frame and transmit it to the Secondary The primary is responsible for receiving an acknowledgment from the Secondary indicating an error free reception The Primary will then poll the Secondary for a response SIMATIC TIWAY I Systems Manual 3 5 Non Siemens Computer Interface Module The TIWAY Adapter A communications device which can be connected to the RS 232 C port of a computer is in development This
221. ure 4 1 The only voting members are the national telecommunications administrations of the member countries The voting representative from the United States is the Federal Communications Commission F CC The International Standards Organization also known as the ISO is responsible for the Open Systems Interconnection 7 layer model Like CCITT thelSO isan international organization it is also a non voting member of CCITT enjoying a close relationship with that organization Membership in ISO is voluntary and is made up of the national standards organizations from member countries The U S representative to ISO is the American National Standards Institute ANSI This organization represents the computer manufacturers of Western Europe Its acronym is ECMA and its membership is around 20 Some U S companies are members those selling computers in Europe ECMA is known for its ability to move rapidly and it often contributes to ISO ANSI represents manufacturers users and communications carriers in the United States Membership is voluntary and it is the U S voicein ISO NBS is a U S Government agency which issues F ederal Information Standards for equipment sold to the federal government EIA is a United States trade organization Its members are U S manufacturers of electronics products EIA is best known for the physical layers RS 232 C standard CCITT s V 24 which specifies the placement and meaning of the pins of the D
222. vided turnkey service and support SIMATIC TIWAY Systems Manual TIWAY Overview 3 483 Chapter 4 Network Architecture 4 1 Introduction eee ra a aa ra ar rn n Network Architecture Purpose of SECTION oes sers nee Fed ddd epee AE dau dee dark Scope of Section coiere O Wed dre A AA aaah Terminology xi e e lie e hole esce Re Ue e E CR QU Ce e bore E pes Races 4 2 Communications Standards Organizations oococccccccc eee Intemational Consultative Committee on Telegraphy and Telephony Intemational Standards Organizations eet tte ees European Computer Manufacturers Association 0 cc cece eee eee eee American National Standards Institute 2 eee U S National Bureau of Standards sisa raimis iiien eet Electronic Industries Association 1 0 0 rr Institute of Electrical and Electronic Engineers 0 cece eee eee Architectures nu eee eee sie EROR eee OL es eee ES Examplesof Layered Architecture 0 0 nns ComputerArchitectures siuii tae iia ka a AAE AA GE aR eas 4 3 OS Model Standard Vendor Implementations sssssssssnsnnnnnnnnnnnsennnn Standards FOTemihn6els iuueosaaeebeR x ER o e mina RC ACRAS KD data 4 4 Open Systems Interconnection OSI Model een nn nnn OSI Model FUNCHONS 5 3 5 ated e dO e oce e eae etre rh ea bd e id Layersand SEICE Sagi einan e aa a a A A A nnn OS SUMMAI aea take eed AAA e I RC ER Noir ae EB eae dera Physical Layer Laye
223. y it too is embedded in a Primitive In this way the complexity of the network operating software is reduced more information is transferred in each message and overall network efficiency is improved To telephone an airline ticket office is to establish communications H owever when one says Please reserve two seats for me on Flight 991 to Phoenix and bill my company he has used a high level protocol that controls both ordering and paying for airline tickets A high level protocol has been implemented on top of the low level protocol which established a link between the caller and theticket office Of course the high level protocols that control Local Area Network processes must have precise definitions and cannot rely on human intelligence to interpret meaning In a LAN such as TI WAY I the high level protocols control the services offered by resources on the network 332 TIWAY Overview SIMATIC TIWAY Systems Manual 3 13 TWAY I Conformant Compatible Products As discussed above TI WAY performance criteria both in data throughput and in station connectivity far exceed that of existing PM550 CIM Local Lines Therefore the two different performance levels have given rise to two categories of Siemens products Category 1 TIWAY conformant equipment defined as any component capable of operating at the higher performance levels utilizing the Higher L evel Primitive coded instructions Category 2 TIWAY compatible eq
224. y can be determined by an instantaneous examination of network traffic For example if message traffic is very heavy along one network data link this layer can route a message along some alternate path assuming an alternate path exists This feature also helps control network congestion Message segmentation is performed here when a packet that is to be transmitted to another station contains too many bits for the data link This layer will break it up into smaller pieces Blocking is the reverse of segmentation The separate parts of a segmented message are taken as they come in off the data link reassembled into one packet and forwarded SIMATIC TIWAY I Systems Manual Network Architecture 4 17 Open Systems inter onnection OSI Model continued Transport Layer OS Layer 4 Inter networking Thisfunction is activated when one network wants to communicate over another network This sublayer appends the necessary data to enable the receiving network to properly route the packet Error Detection Error detection and recovery functions are performed at this layer Errors corrected here are those found in the headers appended only by other network layers NOTE TIWAY has adopted the X 25 International Standard and works in the permanent virtual circuit PVC mode The Transport Layer is the first layer concerned with end to end message integrity It is also responsible for service selection and route selection Only messages
225. y received but undetected or uncorrected but the error control algorithms to total number of bits transmitted Routing A function within a layer totranslatethetitle or address of an entity into a path by which the entity is to be reached Secondary station A slave station in HDLC and ADCCP unbalanced configurations Segmenting A function of an N entity to map one N service unit into multiple N protocol data units Selecting The process of inviting one or more data stations to receive cf Polling Self clocking Transmission in which the clocking information is deduced by transitions within the signal waveform Sequencing A function of an N entity to provide the N service of delivering data in the same order as it was submitted Serial transmission The sequential transmission of a group of bits constituting a character or a frame of data N Service A capability of the N layer which is provided to N 1 entities at the boundary between the N layer and the N 1 layer A 8 Glossary SIMATIC TIWAY Systems Manual N Service access point An association between an N entity and an N 1 entity where N services are offered by the N entity an may be requested by the N 1 entity N Service access poi nt address or N address An identifier which tells where an N service access point may be found used in particular by an N 1 entity when requesting an N connection to tell the N layer where to
226. zes a male plug 25 pin D type receptacle for connection of the communications cable as specified in ISO 2110 Reference L in Appendix C The circuits and pin assignments shown in Figure 5 3 are supported All other pins should beleft vacant to prevent damage which may be caused by non standard pin usage The use of the interchange circuits should conform tothe functional descriptions given in Reference L in Appendix C 9 5 150 RS 232C Name 101 AA Protective Ground 103 BA Transmitted Data 104 BB Received Data 105 CA Request to Send 106 CB Clear to Send 107 CC Data Set Ready 102 AB Signal Ground 109 CF Received Line Signal Detector 114 DB Transmitted Signal Element Timing DCE Source 115 DD Receiver Signal Element Timing DCE Source 10812 CD Data Terminal Ready 1 2 3 4 5 6 7 8 1 Figure 5 3 Low Speed Modem Interface Connector Pin Assignments Line drivers and receivers which meet the requirements of RS 423 A see Reference E in Appendix C and RS 232 C Reference K in Appendix C are used in the modem interface Modem interface data rates are 300 600 1200 2400 4800 9600 and 19 200 bits per second These data rates are user selectable Data rates of 38 400 57 600 and 115 200 are supported with suitable modems The TI WAY modem interface will support asynchronous or synchronous modems and provision is made for user selection of modem type When an asynchronous modem is employed clock enco

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