ALMA Monitor and Control Bus Interface Specification 2001
Contents
1. IF BF FF FF Node Identification First message in address range A node uses CAN Message ID node address 1 2 to identify itself and as the start of the CAN Message ID range to which the slave responds The CAN Message IDs in the range node addresst 1 2 1 to node address 1 2 2 1 are available for use by the slave The allocation and meaning of this range of CAN Message IDs is up to an individual slave implementation This allocation scheme is illustrated in the following table ALMA Project Doc ALMA 70 35 10 03 001 A SPE A ALMA Monitor and Control Bus Date 2001 09 07 ag Interface Specification Status Draft f Draft Pending Approved Released Superceded Obsolete Page 11 of 18 Node Address Node Identification Node CAN Message ID CAN Message ID Range 0 00 04 00 00 00 04 00 01 00 07 FF FF 1 00 08 00 00 00 08 00 01 00 OB FF FF 2 00 0C 00 00 00 OC 00 01 00 OF FF FF 62 00 FC 00 00 00 FC 00 01 00 FF FF FF 63 01 00 00 00 01 00 00 01 01 03 FF FF 2030 1F BC 00 00 1F BC 00 01 1F BF FF FF Each node therefore has 18 bits of CAN messages to respond to and these may be mapped to hardware devices in a node specific way There are 11 bits used to denote the start of the slave CAN Message ID range and this implies a maximum of 2031 slave nodes This number is less than 2047 because the CAN specification mandates that the most significan2. Scan Bus Master transmits IN Periodic Synchronous 50 ms for M amp C messages as 100 defined in table transactions ALMA Project Doc ALMA 70 35 10 03 001 A SPE s M ALMA Monitor and Control Bus Date 2001 09 07 I E Interface Specification Status Draft 4 Draft Pending Approved Released Superceded Obsolete Page 14 of 18 2 2 6 Reset Signal The RS485 reset signal on the interface connector will normally be held at logic 0 FALSE by the master The receiver may be designed so that an open circuit on both lines will be interpreted as logic 0 and a short circuit OV will also be interpreted as logic 0 When the signal is driven to logic 1 TRUE for 1 0 ms or longer the CAN interface circuitry may be returned to its power on state Any activity on the CAN lines may be ignored by the interface for the period extending from 1 0 ms after RESET becomes TRUE until 1 ms after it returns to FALSE The interface shall cease driving the CAN lines and return to its power on state within 0 5 ms of RESET returning to FALSE The master shall not transmit any messages on the CAN bus until at least 1 0 ms after it returns RESET to FALSE This feature will be implemented on the prototype bus master and supported in the wiring of the prototype antennas but it may be deleted from future revisions of this specification Device designers should not assume its existence 2 2 7 Timing Signal The sou
3. K provided that YK i lt N max where Nmax is 2031 i l 3 Each branch typically serves a rack or large chassis Each node is typically embedded in a module level assembly 4 Any node can be removed or inserted without disturbing communication to others Figure 3 ALMA CAN bus topology ALMA Project Doc ALMA 70 35 10 03 001 A SPE A ALMA Monitor and Control Bus Date 2001 09 07 a ag Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 10of18 2 2 Node Connection Protocol In order to satisfy M amp C requirements of determinism and flexibility a protocol governing the master slave behavior must be implemented above the CAN protocol Several proprietary products exist to address this sort of problem Device Net and SDS but most are targeted at turn key industrial process control markets In addition there are several competing open protocols such as CAL CAN Open and CAN Kingdom Here we adopt a simpler protocol while attempting to preserve interoperability with commercial products that support one of the higher level protocols A commercial product using CAL has been tested in conjunction with the simple protocol outlined here A simple node identification protocol is outlined in the following sections which examine the most important scenarios Section 2 2 6 summarizes those events external to the bus system which will be handled by this pro
4. its CAN Message ID range The master may not know that the slave node has been inserted unless it attempts communication with the node or issues a bus identification broadcast When a node is removed the master will not notice unless it attempts transmission to the slave When this occurs it should flag the error and continue ALMA Project Doc ALMA 70 35 10 03 001 A SPE A ALMA Monitor and Control Bus Date 2001 09 07 e a H Interface Specification Status Draft S ba Draft Pending Approved Released Superceded Obsolete 2 Page 12of18 2 2 3 Message Content We distinguish two types of CAN message sent from the master monitor requests and controls The AMB master will ensure that all consecutive CAN transactions to a single slave node occur at least 300 us apart 2 2 3 1 Monitor Signals Monitor data is requested by sending a CAN message with no data Remote transmissions frames are not used due to the way that the CAN controllers implement CAN Message ID filtering Note that this implies that all control messages must have at least one byte of possible dummy data The slave node responds with a transmission of a CAN message with the same CAN Message ID and containing the requested monitor data Slaves must begin transmission of a response within 150 us of receiving a monitor request 2 2 3 2 Control Signals A control signal is sent by passing the data in a CAN message with one to eight byt
5. Atacama Large Millimeter Array ALMA Monitor and Control Bus Interface Specification ALMA 70 35 10 03 001 A SPE Version A Status Draft Pending Approved Released or Obsolete 2001 09 07 Prepared By Name s and Signature s Organization Date Mick Brooks NRAO 2001 09 07 Larry D Addario NRAO Approved By Name and Signature Organization Date B Glendenning NRAO 7 22 03 Released By Name and Signature Organization Date XXX XXX yyyy mm dd A gt Df lt ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 a Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 2 of 18 Change Record 1999 09 22 Mick Brooks First public release B 1999 12 09 Mick Brooks All Fixed block diagram to current state of standard interface C 2000 02 29 Mick Brooks All Review comments included D 2000 04 18 Mick Brooks All Post review comments clarification of reset Larry D Addario line added E 2001 01 17 Mick Brooks All Removed details of AMBSI hardware Larry D Addario merged with Timing Addendum fixed up maximum number of slave nodes added circular connector added RS485 bus for timing signal First release as an ALMA wide specification ALMA document number assigned F 2001 01 26 Mick Brooks All Comments from d
6. cial PV CIS cesna erren ai r E E E E AT AEE AE E 13 2 2 6 Reset Signal iirinn a EEE R ENEA EERE DETR ERGEN 14 2 2 1 Miming Signal emesene nene rere EES ERAR EEEE EEEE OSEE ER EE EAEE EER 14 3 TIMING OF COMMANDS AND MONITOR REQUESTS 0 ceececeeseeseeeteeseeeseeeeeees 14 31 DIRT OMS eiin nera EEE AE EE AT AE EER 14 32 Specificato scot ges a ees ad cm cent E TEE A EE E 14 3 3 DISCUSSION sorniera E cna E E EE cade cd dca emo eee 17 REFERENCES sccacesauiancenubtenctassanaeanaloeceayuueaGuiuee acevo santo ospactataueeovahisaoess E ANE ESA 18 ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 4 of 18 1 Introduction This document specifies the ALMA Monitor and Control Bus interface Section 2 lays down the fundamental requirements that must be met by all nodes on the bus In Section 2 1 the method for physical connection of nodes to the bus is given An application level protocol to which all M amp C nodes must conform is outlined in Section 2 2 In order for a subsystem to work with the ALMA M amp C Bus it is sufficient for the interface to conform to the standards presented in Section 2 Section 3 specifies how some bus messages may be synchronized to a precise timing signal distributed separately The application level protocol is simple but implies that each M amp C bus i
7. ect Interface Specification Na ALMA Monitor and Control Bus FA EA Date Status Draft Pending Approved Released Superceded Obsolete Page 13 of 18 Doc ALMA 70 35 10 03 001 A SPE 2001 09 07 Draft 2 2 5 Special Events The monitor and control bus is considered to be a real time subsystem of its own and the following table outlines those events which may impinge on it and how it should react The event list is a detailed list of the environmental events that are of interest to the bus system The list defines not only the events but also the expected system response their arrival patterns and the event source Nominal response times for each event are also given Event System Response Direction Arrival Synchronization Response Pattern Bus a Master I Episodic Asynchronous 150 ps per Identification prompts nodes Cur node address 11 ms for b slaves respond conflicts 64 nodes with serial detected number c master resolves address conflicts Node Inserted lt internal gt Episodic Asynchronous N A a slave begins OUT responding to in range M amp C messages immediately b master detects through bus identify Node Removed lt internal gt ls a master detects OUT if scanning b slave flagged as not responding CAN Failure lt internal gt Episodic Asynchronous 20 ms a master stops OUT scanning b master flags CAN failure c slaves reset
8. elta review incorporated G 2001 02 05 Mick Brooks All Additional comments included from D Addario and Gustafsson H 2001 09 07 Mick Brooks All Added specification on maximum rate of Master transactions to a single node I 2003 05 26 L Cryer All Reformatted J 2003 10 01 R Marson Title Only Document number changed ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 3 of 18 Table of Contents 1 INTRODUCTION cca cae cea aaa pase wines ER E EET 4 2 M amp C BUS INTERFACE cro ent a E E E EEEE E E REEE 5 2 1 Physical Stand ats 2s ccsanswxacnasvssucsavapnsssecwastsnesionscuandiouineernacdseamenessbaxetessmmestioulacscuounens 5 2 1 1 Physical Layer and Media Access Protocol s cscssiecsssisecssasnedassnsninesdeansdanthabegneesentianas 5 2 1 2 Physical INCE C OMIM CHM asc siesicaccesysncncarcaiensivendcxeseaddaoanansianen Geena aermantemennes 5 2 2 Node Conn ction PrototO a lt sisen ci csesdvnsaasdanescniceussnantennsdsesusmasiindateduacndabeismscinesecineetabess 10 2 2 1 Bus WAM TI CATION iesise sianseseubeadGaiinds sndissacatave AA ER 11 2 2 2 Node Insertion and Removal cxcudecccancizie avs eassacpansesecaraurtaescentraansencsetvnctescesmiveatennts 11 22 3 Mess ge Content aeren a E E E E 12 224 Erroi SituatioNS asirica retorinen Ea eE a E aE E E AER 12 2 29 Spe
9. es of data Note that no control message can have zero bytes of data as this indicates a monitor transaction The acknowledgement bit in the message trailer will inform the master that some slave detected a valid message but it does not indicate that it was correctly received by the destination node Verification of successful transmission requires a subsequent monitor request 2 2 4 Error Situations Transmission errors are handled by the CAN interface hardware As CAN frames are received or transmitted successfully error counters in the CAN interface hardware are decremented When errors occur these counters are incremented When the counters reach 256 excessive transmission errors the node goes bus off and ceases responding See 1 for more details on this behavior Entering the bus off state will generate a hardware interrupt and the slave or master can attempt remedial action tis Automatic Action by ALMA Error Condition Detecten By Action by CAN Solare i Master Hardware or Slave Excessive transmission errors Slave Slave ceases None CAN controller bus off state responding Excessive transmission errors Master Master ceases Master resets its own CAN controller bus off state transmitting interface Duplicate Node address Slave None Slave ceases responding Duplicate Node address Master None Master flags error Slave does not respond Master None Master flags error timeout 4 ALMA Proj
10. iate the monitor request or command with a different TE than the one intended If a particular device behaves in any other way such as ignoring a monitor request or command received outside some time limits then this should be described in the appropriate ICD ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 18 of 18 References 1 ALMA Monitor and Control System Mick Brooks 1999 05 10 2 CAN Specification Version 2 0 Philips Semiconductors Unternehmensbereich der Philips GmbH 1991 3 CAN System Engineering Wolfhard Lawrenz Springer Verlag 1997 4 ALMA Monitor and Control Bus Requirements Mick Brooks 1999 04 08 5 The T C bus Specification Version 2 0 Philips Semiconductors December 1998 6 C167 Derivatives User s Manual Siemens AG March 1996 7 Standard for electrical characteristics of generators and receivers for use in balanced digital multipoint systems EIA Standard RS 485 Electronic Industries Association 1983 8 CANopen Cabling and Connector Pin Assignment CiA Draft Recommendation DR 303 1 Version 1 0 October 10 1999
11. ignal line A c TIMB Timing Signal line B D Reserved for power distribution E Reserved for power ground F Reserved G RSTA Global Slave Node Reset line A H RSTB Global Slave Node Reset line B J CAN L CAN L bus line dominant low K CAN G CAN Ground ND L CAN_SH CAN Bus Shield LD The maximum stub length for a drop line from the trunk to a CAN node is 0 3 m Bus nodes will each provide a single connector Trunk sections will have a male connector at one end and a female connector at the other Trunk connections will be passive and consist of 1 male connector and 1 female connector with a stub line to the connector on a device ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 9of 18 The use of additional pins for a global reset signal and for the distribution of the 48ms timing signal is an ALMA extension to the CAN specification Each signal will be transmitted as a differential RS485 signal as defined in 7 The logical details of the signals are described in Section 0 and Section 0 The RS485 receiver in each node shall present no more than 1 4 of a unit load to the bus A suitable transceiver is the MAX3082 used in receive only mode CAN_GND should be tied to the CAN bus zero voltage reference within each connected node CAN_SHLD will be connected to the ou
12. ing Approved Released Superceded Obsolete Page 5o of18 2 M amp C Bus Interface 2 1 Physical Standards 2 1 1 Physical Layer and Media Access Protocol The low level protocol to be used will be the Controller Area Network version 2 0 B as described in 2 The B version allows for up to 2 CAN Message IDs The A version which has an 11 bit address range will not be used but hardware used in the implementation will not preclude devices using this format Each CAN message is a packet with a fixed identifier the CAN Message ID and exactly one transmitter node and any number of receiver nodes The CAN specification defines both the Physical Layer and the Media Access Layer of the ISO 7 layer protocol model The CAN bus will be operated at 1 Mbps the maximum rate for all twisted pair connected buses Where fiber optic media converters are used the maximum transmission rate is 250kbps It is intended that a mixture of Full and Basic CAN controller implementations will be used to address the various data rate requirements of the ALMA M amp C See 3 for a description of Full and Basic CAN All monitor and control bus transactions will be initiated by the master The remote frame transmission request RTR will not be used by the bus master to gather monitor data Instead monitor requests will be achieved by the bus master writing a CAN Message to the bus with no data The slave node responds by writing a CAN Message co
13. ncreasing time 48 ms ticks TE TE TE o o iss Nae associated command transmit with command window 24ms 48ms Figure 4 TE associated command timing ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page l6of18 Increasing time 48 ms ticks TE TE TE oN time associated KE S monitor request monitor request transmit window 24ms 20ms 4ms 4 lt lt 48ms Figure 5 TE associated monitor timing ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 17 of 18 3 3 Discussion In these situations we say that the command is associated with the TE that immediately follows it or that the monitor request is associated with the TE that immediately precedes it The actual sampling time of monitor data or application time of command data is dependent on the device s design These may be offset from the associated TEs if appropriate All such details should be given in the relevant part of an ICD Devices are not required to check that the timing of CAN frames complies with this specification If the bus master fails to comply then the device may assoc
14. nd Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 7 of 18 1 2 3 4 5 O O O O RSTA CANL CAN GND TIMA CAN SHL e 6 7 8 9 O O O G O RSTB CANH TIMB A male connector is shown viewed from the pin side both male and female connectors are used as shown in Figure 3 Table 1 9 pin D sub Connector Pin allocations Pin Signal Description i me Global Slave Node Reset line A 2 CAN L CAN L bus line dominant low 3 CAN GND CAN Ground 4 TIMA Timing Signal line A 5 CAN SHLD CAN Bus Shield 6 RSTB Global Slave Node Reset line B 7 CAN H CAN H bus line dominant high 8 TIMB Timing Signal line B 9 Reserved for power distribution ALMA Project Doc ALMA 70 35 10 03 001 A SPE Re w ALMA Monitor and Control Bus Date 2001 09 07 as Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 8of 18 Oo H RSTB K Figure 2 AMB 11 pin Amphenol circular connector pin allocations A male connector is shown viewed from the pin side both male and female connectors are used as shown Figure 3 Table 2 11 pin Amphenol Circular Connector Pin allocations Pin Signal Description i PACH CAN _H bus line dominant high B TIMA Timing S
15. ntaining the requested data RTR can not be used over a range of CAN Message IDs as is intended by this protocol Control data is simply transmitted by the master and the CAN acknowledge bit is used to verify correct slave reception Control messages must always have 1 to 8 bytes of data In order to meet the requirements outlined in 4 an additional higher level protocol will be necessary for node management and to govern the transfer of data Aspects of this protocol are outlined in Section 2 2 All slave nodes must use Philips 82C250 transceivers and preferentially Intel 82527 compatible CAN controllers 2 1 2 Physical Interconnection The bus interconnections use differential signaling on a twisted pair transmission line of 120 ohms impedance 4 as defined in ISO 11898 The CAN bit timing characteristics allow for a 35 meter maximum run length at 1 Mbps The cable used should be double shielded Suitable cable types for the CAN signals are Belden type 3082A for trunk cabling and type 3084A for drop cables Smaller diameter cables include Belden type 3085 Whereas we also specify wires for a global reset signal and a timing signal as explained later and possibly for power distribution other cable types with similar characteristics but with additional wires should be used ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Appro
16. nterface unit has a Node Address in the range 0 2030 and a unique 64 bit Serial Number which should be provided by a component from the Dallas Semiconductor Silicon Serial Number family such as the DS18S20 The node address may be specified by the ALMA Computing Group or could be settable on the interface by means of a DIP switch or other appropriate means The ALMA M amp C Bus AMB is envisaged as a master slave multi drop serial bus used for communication with each antenna subsystem Some subsystems destined for the central control building will also be accessed with the AMB The design described herein is based on a Controller Area Network CAN serial bus operated in a master slave mode by a dedicated bus master The application level protocol in Section 2 2 defines a polled method for accessing slave nodes from a bus master and for communications to and from individual slave nodes with the relevant CAN Message IDs In the operational environment of the ALMA telescope the bus master will be an embedded computer running a real time operating system In a laboratory testing environment the master may be a PC or other general purpose computer running a user based operating system such as some version of Windows or Unix See 1 for details on the rationale behind this design ALMA Project Doc ALMA 70 35 10 03 001 A SPE aA ALMA Monitor and Control Bus Date 2001 09 07 K ag Interface Specification Status Draft Draft Pend
17. rce of the timing signal will not necessarily be the master node of the CAN bus but may be some other node The source will contain an RS485 transmitter which will drive the bus to a quiescent state of logic 0 FALSE and will drive it to logic 1 TRUE periodically with a duty cycle between 1 and 25 The period is currently specified to be 48 0 ms Use of the signal at other nodes is optional but each user node shall have an RS485 receiver that is designed so that an open circuit or short circuit is interpreted as logic 0 The leading edge 0 to 1 transition of the signal will be accurately synchronized to ALMA array time with a maximum error to be specified elsewhere but the timing of the falling edge 1 to 0 is not specified 3 Timing of Commands and Monitor Requests 3 1 Definitions A timing event TE is the positive going transition of the low frequency periodic reference signal The time of receipt of a command or monitor request is the time that the last bit of the CAN frame is transmitted on the bus by the bus master 3 2 Specification By default every command transmitted to a device over the ALMA Monitor control Bus AMB is effective immediately upon receipt and every monitor request should return the most recent data available at the time the request is received However under some circumstances the effective times may be different as described in the following paragraphs These commands are sometimes referred to a
18. s time critical When specified in an Interface Control Document ICD a specific command may be considered effective at a later time than its time of receipt In all such cases the command is associated with the timing event TE that immediately follows receipt of the command See Figure 4 ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor and Control Bus Date 2001 09 07 Interface Specification Status Draft Draft Pending Approved Released Superceded Obsolete Page 15 of 18 When specified in an ICD a specific monitor request may be required to return data that was acquired at an earlier time In all such cases the monitor request is associated with the TE that immediately precedes receipt of the request See Figure 5 As shown in Figure 4 the monitor control system may begin transmission of a CAN frame carrying a TE related command no earlier than the occurrence of a TE and it must complete the transmission no later than 24 ms after that TE That is all such commands must be transmitted during the first half of the 48 msec interval between TEs As shown in Figure 5 the monitor control system may begin transmission of a monitor request CAN frame no earlier than 24 ms after a TE and it must complete the transmission no later than 4 ms before the next TE That is all such monitor requests must be transmitted during a 20 ms window in the last half of the 48 msec interval between TEs I
19. t 7 bits of the CAN ID must never be all 1s In addition the range of CAN Message IDs up to the first slave node range is available for future allocation of broadcast messages At present the only broadcast defined is CAN Message ID 0 used for the node identification sequence Others may be allocated for use during interface discussions with subsystem designers 2 2 1 Bus Identification After the master broadcasts the CAN message requesting slaves to identify themselves CAN Message ID 0 each slave writes to the node specific identification CAN Message ID with its unique Serial Number as data The master may detect duplicate Node Addresses if a slave tries to use a Node Address which is already in use A slave station may detect a duplicate Node Address if two slaves begin transmitting to the same Node Address slot at the same time but with different Serial Numbers In this case the slave with the higher Serial Number will detect a transmission error during the data section and will cease transmitting as that node Slave nodes should respond to a bus initialize request within 1 ms If the bus is idle for a period of 1 ms during the identification process the bus master will assume that all slaves have identified themselves and will begin normal bus operation This sequence may be initiated by the master at any time 2 2 2 Node Insertion and Removal When a node is inserted the node immediately begins responding to transactions within
20. ter shield of the cable Use of CAN SHLD within a node is optional the recommended use is to connect it to local ground through a small resistor 10 100 ohms Provision may be made for the use of repeaters such as optical to extend the stub length or to create low emission or low susceptibility bus segments Currently available transceivers limit the number of nodes on a single bus to 64 This may be extended by the use of repeaters or by driving several physical busses from one master while maintaining a single logical bus There is a logical limit of 2031 nodes per bus imposed by the protocol defined in Section Error Reference source not found below Trunk Connectors _ Y Trunk 35m Max per CAN Spec They DIE wt a Aa a Termination Ei lt lt 124 ohms lt Bus Master AN A A Branch 1 A Branch 2 Branch L Termination Node base Node Node 124 ohms a 1 1 T piece zi L1 Node Node Node 1 2 2 2 L2 0 3m max stub Node Node Node LK lt lt 2 K2 lt lt L K l no term 1 Node connectors are not part of this specification They may be device dependent They also may involve several connectors from stub module interface board L 2 No limit on number of nodes per branch
21. tocol The protocol is based on the reservation of a CAN Message ID range one for each node for use in node specific communication with the master The node protocol retains a master slave relationship with the master responsible for detecting most duplicate node address errors This also means that message collisions will not occur except in one case When the master initializes the bus it broadcasts a request for all nodes on the bus to identify themselves Collisions may occur as nodes try to send their Node Addresses and Serial Numbers In normal operation however all message transactions will be initiated by the master and no collisions will occur The Node Address for each slave node is adjustable by a DIP switch backplane position or other method that allows it to be stored locally in a non volatile manner Each Node Address must be unique within a single bus It determines the range of CAN message IDs to which that node will respond In addition each physical interface device used to connect a node to the bus is assigned a permanent Serial Number which is unique throughout all ALMA hardware It is intended that high level software will maintain tables from which each device s characteristics can be determined from its Serial Number The following CAN Message ID usage is defined Usage CAN Message ID hex Bus Initialize 00 00 00 00 Available for Broadcasts 00 00 00 01 00 03 FF FF M amp C Data 00 04 00 00
22. ved Released Superceded Obsolete Page 6of 18 The connection of a chassis or subsystem to the bus is accomplished with a pair of connectors male and female to which sections of trunk cable are connected see Figure 3 Normally the connectors are 9 pin D subminiature type as is the industry standard for CAN 8 Figure 1 and Table 1 show the pinout of this connector However when the connection is to be exposed to the environment an Amphenol type MS3112E18 11S or MS3112E18 11P socket and plug part numbers respectively 11 pin circular connector should be used Figure 2 and Table 2 show the pinout of this connector No connector type other than these two shall be used for bus trunk connections In the bus topology illustrated in Figure 3 the bus trunk connects subsystems or chassis with D or circular connectors one of each sex A stub line extends throughout each chassis and each local CAN node attaches to the stub using connectors that may vary among devices and that may carry additional device dependent signals The bus requires termination at both ends with 124 Q resistors capable of dissipating 200 mW To preserve the possibility of interoperability of the ALMA bus with commercial CAN devices the interconnections specified here follow those in 8 as much as possible sa Fe P Figure 1 AMB D connector pin allocations ALMA Project Doc ALMA 70 35 10 03 001 A SPE ALMA Monitor a
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