Isolator488 Users Manual
Contents
1. gt E ENQ ed PPU 06 6 16 26 s pr 6 66 76 ACK SYN bc T e 71867 103 877 see d dum d ec 104 78 bs e ep 9 69 5 79 See T Tes l MM DES LE 8 18 GAN SPE Si Ee Ta ut ia 0 1A oR SUB 10 GG d de 0C 12 aM sc Ke 108 P FF SCG se 0D 13 u ES sk 6D 109 SC CR a di de EN is OBIE dan pe MISES d e 110 7E SCG Gr d MEO ES i E d Q d ui 3 Tot gi 27 47 E d iaa 4B ge rp E 0 TE 4 6A 10 d Reg ge ei 107 SCG ui 37 us 3A 3B 3C 3b ACG Addressed Command Group TAG Talk Address Group UCG Universal Command Group SCG Secondary Command Group LAG Listen Address Group Al2. IEEE 488 Primer History General Structure Send It To My Address Bus Management Lines Attention ATN Interface Clear IFC Remote Enable REN End Or Identify EOI Service Request SRQ Handshake Lines Data Valid DAV Not Ready For Data NRFD Not Data Accepted NDAC Data Lines Multiline Commands Page 1 1 1 1 1 2 1 3 Page 2 1 2 1 24 24 2 0 2 10 2 11 2 11 2 12 2 13 2 13 Section 3 cont 3 7 1 3 7 2 3 7 3 3 7 4 3 7 5 3 7 6 3 7 7 3 7 8 3 7 9 3 7 10 3 7 11 3 7 12 3 7 13 3 7 14 3 7 15 3 8 3 8 1 3 8 2 Section 4 4 1 Appendix A Go To Local GTL Listen Address Group LAG Unlisten UNL Talk Address Group TAG Untalk UNT Local Lockout LLO Device Clear DCL Selected Device Clear SDC Serial Poll Disable SPD Serial Poll Enable SPE Group Execute Trigger GET Take Control TCT Secondary Command Group SCG Parallel Poll Configure PPC Parallel Poll Unconfigure PPU More On Service Requests Serial Poll Parallel Poll SERVICE INFORMATION Factory Service Character Codes and IEEE Multiline Messages Section 1 Introduction Introduction 1 4 GENERAL DESCRIPTION The Isolator488 increases the number of IEEE instruments and devices allowable on the bus from 15 including the controller to 28 while also providing optical isolation between the system controller and devices on the isolated bus Since the Isolator488 does not occupy a bus address its o
3. Instrument Port Controller Common Instrument Common Controller Shield Instrument Shield Getting Started The Ground terminal on the AC power cable This is internally connected to the chassis of the Isolator488 The IEE 488 port labeled CONTROLLER on the rear panel of the Isolator488 The system controller must be connected to this port Instruments may also be connected to this port but instruments placed in the CONTROLLER port will not be isolated from the system controller The IEEE488 port labeled INSTRUMENTS on the rear panel of the Isolator488 Instruments may be connected to this port Instruments connected to the Instrument Port may be isolated from devices on the Controller Port depending on the internal configuration of the Isolator 488 The logic common connection on the Controller Port Pins 18 19 20 21 22 23 and 24 of the Controller Port are all connected to Controller Common The logic common connection on the Instrument Port Pins 18 19 20 21 22 23 and 24 of the Controller Port are all connected to Instrument Common The Shield connection Pin 12 on the Controller Port The Shield connection Pin 12 on the Instrument Port The factory configuration of the Isolator488 is as follows 2 2 Section 2 Getting Started 2 3 Section 2 Getting Started As shown in the preceding diagram the Isolator488 is shipped with a soft ground consisting of a 1 MQ resistor in parallel with a 0 01 uF
4. Refer to the following figure 2 4 Getting Started Section 2 SLN3IAFTHISNI OL W3TIOHLNOO OL KS EE SjueuoduiJo j UOWWO7 UOd ZU euunugsu ev 8v2 199 EE st SjueuoduiJo 9 uouJuJo 3 uod J9 Ouo MITA CULO SSp ioje osq 2 5 Section 2 Getting Started The following options are available on each port 1 The Shield pin of the IEEE 488 connector pin 12 may be connected to the logic common of the IEEE 488 connector pins 18 19 20 21 22 23 and 24 or left unconnected 2 Logic common of IEEE 488 connector pins 18 19 20 21 22 23 and 24 may be connected to the chassis of the Isolator488 connected to the chassis through a soft ground or left unconnected The following changes may be made to the Controller Port 1 To remove the Controller common from earth ground remove R4 and C16 by either desoldering the components the bottom panel or the Isolator488 must be removed in order to do this or cutting the component leads so that they may be removed Make note of this change for later reference 2 To connect Controller common to earth ground insert a 1 2 amp fuse in the fuse clips labelled F2 The 1 2 amp fuse connects the Controller common to earth ground and limits fault currents to 1 2 amp Make note of this change for later reference 3 To connect pin 12 shield of the Controller Port to Controller Common solder a jumper wire in the location labeled JPR1 Make note of this chang
5. CE Notice Many IOtech products carry the CE marker indicating they comply with the safety and emissions standards of the European Community As applicable we ship these products with a Declaration of Conformity stating which specifications and operating conditions apply Warnings Cautions Notes and Tips Refer all service to qualified personnel This caution symbol warns of possible personal injury or equipment damage under noted conditions Follow all safety standards of professional practice and the recommendations in this manual Using this equipment in ways other than described in this manual can present serious safety hazards or cause equipment damage This ESD caution symbol urges proper handling of equipment or components sensitive to damage from electrostatic discharge Proper handling guidelines include the use of grounded anti static mats and wrist straps ESD protective bags and cartons and related procedures Specifications and Calibration Specifications are subject to change without notice Significant changes will be addressed in an addendum or revision to the manual As applicable IOtech calibrates its hardware to published specifications Periodic hardware calibration is not covered under the warranty and must be performed by qualified personnel as specified in this manual Improper calibration procedures may void the warranty Quality Notice TSO IOtech has maintained ISO 9001 certification since 1996 Prior to sh
6. Group LAG There are 31 0 to 30 listen addresses associated with this group The 3 most significant bits of the data bus are set to 001 while the 5 least significant bits are the address of the device being told to listen 3 7 3 Unlisten UNL This command tells all bus devices to Unlisten The same as Unaddressed to Listen 3F 3 7 4 Talk Address Group TAG There are 31 0 to 30 talk addresses associated with this group The 3 most significant bits of the data bus are set to 010 while the 5 least significant bits are the address of the device being told to talk 3 7 5 Untalk UNT This command tells bus devices to Untalk The same as Unaddressed to Talk 5F 3 7 6 Local Lockout LLO Issuing the LLO command prevents manual control of the instrument s functions 11 3 7 7 Device Clear DCL This command causes all bus devices to be initialized to a pre defined or power up state 14 3 8 Section 3 IEEE 488 Primer 3 7 8 Selected Device Clear SDC This causes a single device to be initialized to a pre defined or power up state 04 3 7 9 Serial Poll Disable SPD The SPD command disables all devices from sending their Serial Poll status byte 19 3 7 10 Serial Poll Enable SPE A device which is Addressed to Talk will output its Serial Poll status byte after SPE is sent and ATN is unasserted 18 3 7 11 Group Execute Trigger GET This command usually signals a group of devices to begin
7. a computer Before any information transfer can take place it is first necessary to specify which will do the talking send data and which devices will be allowed to listen receive data The decision of who will talk and who will listen usually falls on the System Controller which is at power on the Active Controller The System Controller is similar to a committee chairman On a well run committee only one person may speak at a time and the chairman is responsible for recognizing members and allowing them to have their say On the bus the device which is recognized to speak is the Active Talker There can only be one Talker at a time if the information transferred is to be clearly understood by all The act of giving the floor to that device is called Addressing to Talk If the committee chairman can not attend the meeting or if other matters require his attention he can appoint an acting chairman to take control of the proceedings For the GPIB this device becomes the Active Controller 3 1 Section 3 IEEE 488 Primer At a committee meeting everyone present usually listens This is not the case with the GPIB The Active Controller selects which devices will listen and commands all other devices to ignore what is being transmitted A device is instructed to listen by being Addressed to Listen This device is then referred to as an Active Listener Devices which are to ignore the data message are instructed to Unlisten The reaso
8. executing a triggered action This allows actions of different devices to begin simultaneously 08 3 7 12 Take Control TCT This command passes bus control responsibilities from the current Controller to another device which has the ability to control 09 3 7 13 Secondary Command Group SCG These are any one of the 32 possible commands 0 to 31 in this group They must immediately follow a talk or listen address 60 to 7F 3 9 Section 3 IEEE 488 Primer 3 7 14 Parallel Poll Configure PPC This configures devices capable of performing a Parallel Poll as to which data bit they are to assert in response to a Parallel Poll 05 3 7 15 Parallel Poll Unconfigure PPU This disables all devices from responding to a Parallel Poll 15 3 8 MORE ON SERVICE REQUESTS Most of the commands covered both uniline and multiline are the responsibility of the Active Controller to send and the bus devices to recognize Most of these happen routinely by the interface and are totally transparent to the system programmer Other commands are used directly by the user to provide optimum system control Of the uniline commands SRQ is very important to the test system and the software designer has easy access to this line by most devices Service Request is the method by which a bus device can signal to the Controller that an event has occurred It is similar to an interrupt in a microprocessor based system Most intelligent bus peripher
9. ready to accept new data The Talker must wait for each Listener to unassert this line high which they will do at their own rate when they are ready for more data This assures that all devices that are to accept the information are ready to receive it 3 5 3 Not Data Accepted NDAC The NDAC line is also controlled by the Listeners This line indicates to the Talker that each device addressed to listen has accepted the information Each device releases NDAC high at its own rate but the NDAC will not go high until the slowest Listener has accepted the data byte 3 6 Section 3 IEEE 488 Primer 1st Data Byte 2nd Data Byte DIO 1 8 composite DAV valid Not valid Not il Valid Valid NRFD All None All None Acceptor Ready Ready Ready Ready NDAC None All None All Acceptor Accept Acce IEEE Bus Handshaking 3 6 DATA LINES The GPIB provides eight data lines for a bit parallel byte serial data transfer These eight data lines use the convention of DIO1 through DIO8 instead of the binary designation of DO to D7 The data lines are bidirectional and are active low 3 7 MULTILINE COMMANDS Multiline bus commands are sent by the Active Controller over the data bus with ATN asserted These commands include addressing commands for talk listen Untalk and Unlisten 3 7 1 Go To Local GTL This command allows the selected devices to be manually controlled 01 3 7 Section 3 IEEE 488 Primer 3 7 2 Listen Address
10. used for bus management Signals on these lines are often referred to as uniline single line commands The signals are active low i e a low voltage represents a logic 1 asserted and a high voltage represents a logic 0 unasserted 3 4 1 Attention ATN ATN is one of the most important lines for bus management If Attention is asserted then the information contained on the data lines 1s to be interpreted as a multiline command If it is not then that information is to be interpreted as data for the Active Listeners The Active Controller is the only bus device that has control of this line 34 Section 3 IEEE 488 Primer 3 4 2 Interface Clear IFC The IFC line is used only by the System Controller It is used to place all bus devices in a known state Although device configurations vary the IFC command usually places the devices in the Talk and Listen Idle states neither Active Talker nor Active Listener 3 4 3 Remote Enable REN When the System Controller sends the REN command bus devices will respond to remote operation Generally the REN command should be issued before any bus programming is attempted Only the System Controller has control of the Remote Enable line 3 4 4 End or Identify EOI The EOI line is used to signal the last byte of a multibyte data transfer The device that is sending the data asserts EOI during the transfer of the last data byte The EOI signal is not always necessary as the end of t
11. 488 Bus Isolator are accessories for rack or bench use If rack mount installation is required install the two rack ears using the enclosed screws These ears can be installed so either the front or the rear of the unit faces the front of the rack fixture View of Enclosure showing Rack Hardware Installation Enclosure Top or Bottom View qu RackEar Screw 2perear If bench installation is required the rubber feet can be installed on the underside of the unit near each corner View of Enclosure Bottom Showing Feet Placement Enclosure Bottom View 2 9 Section 2 Getting Started 2 6 Operation To begin operating the Isolator488 plug the power supply into the rear panel jack Apply power to the Isolator488 by depressing the rear panel power switch The front panel POWER LED should turn on If the POWER indicator does not light there may not be any power supplied to the interface In this event check to make sure the AC power is supplied to the Isolator488 and that the power cord is properly installed into the unit If the problem is unresolved refer to the Service Information section Section 4 of this manual If proper operation is obtained turn off the Isolator488 and connect the other IEEE 488 devices to each of the Isolator488 ports Apply power to all devices in the system Once all IEEE devices have been connected and powered on the Isolator488 will allow the system controller to command up to 13 IEEE
12. Enable Service Request Talker Active Talker Address Take Control Terminator Unlisten Untalk Unasserted Section 2 Getting Started GETTING STARTED 2 1 Inspection The Isolator488 was carefully inspected mechanically and electrically prior to shipment When you receive the interface carefully unpack all items from the shipping carton and check for any obvious signs of physical damage which may have occurred during shipment Report any damage to the shipping agent immediately Remember to retain all shipping materials in the event that shipment back to the factory becomes necessary Every Isolator488 is shipped with the following Isolator488 IEEE Bus Isolator e 123 0900 Instruction Manual e 123 0800 Accessory Kit includes power cable fuse and rack mounting hardware 2 2 Configuration Before using the Isolator488 you should be aware of the connections between the IEEE digital commons the shield lines on each bus and earth ground The following information is provided so that you can determine if the factory configuration is appropriate for your application or if some changes need to be made prior to use The following is a list of terms and their definitions as used in this manual Isolation The ability of the Isolator488 to break the electrical connection between the shields and digital commons of its IEEE 488 ports while allowing the transfer of data 2 1 Section 2 Earth Ground Controller Port
13. Isolator488 IEEE 488 Bus Isolator USER S MANUAL Orch lOtech Inc 25971 Cannon Road Cleveland Ohio 44146 440 439 4091 Warranty Information Your IOtech warranty is as stated on the product warranty card You may contact IOtech by phone fax machine or e mail in regard to warranty related issues Phone 440 439 4091 fax 440 439 4093 e mail sales iotech com Limitation of Liability IOtech Inc cannot be held liable for any damages resulting from the use or misuse of this product Copyright Trademark and Licensing Notice All IOtech documentation software and hardware are copyright with all rights reserved No part of this product may be copied reproduced or transmitted by any mechanical photographic electronic or other method without IOtech s prior written consent IOtech product names are trademarked other product names as applicable are trademarks of their respective holders All supplied IOtech software including miscellaneous support files drivers and sample programs may only be used on one installation You may make archival backup copies FCC Statement IOtech devices emit radio frequency energy in levels compliant with Federal Communications Commission rules Part 15 for Class A devices If necessary refer to the FCC booklet How To Identify and Resolve Radio TV Interference Problems stock 004 000 00345 4 which is available from the U S Government Printing Office Washington D C 20402
14. MENT DIMENSIONS WEIGHT CONTROLS SUPPLIED ACCESSORIES ISOLATION Introduction 85 nStyp 120 nS Max 90 nS typ 125 nS Max 355 nS typ 475 nS Max 155 nS typ 2075 nS Max 85 nStyp 120 nS Max 90 nStyp 125 nS Max 140 nS typ 205 nS Max Bidirectional Bidirectional To Local Bus To Remote Bus Bidirectional Two IEEE 488 connectors with metric studs LED for Power 105 125V or 210 250V 50 60 Hz 20 VA MAX 0 to 50 C 0 to 70 RH 425 mm deep x 45 mm wide x 208 mm high 16 75 x 1 75 x 8 20 2 1 kg 4 6 Ibs Power switch Power cable and manual IEEE 488 common on Controller Bus to IEEE 488 common on Instrument Bus 1600 volts peak maximum sea level to 10 000 ft 0 70 C and 0 80 RH non condensing OR 500 Vac maximum 10 V Hz Specifications are subject to change without notice Section 1 1 4 Abbreviations Introduction The following IEEE 488 abbreviations are used throughout this manual addr n ATN CA CR data DCL GET GTL LA LAG LF LLO MLA MTA PPC PPU SC SDC SPD SPE SRQ TA TAD TCT term UNL UNT IEEE bus address n Attention line Controller Active Carriage Return Data String Device Clear Group Execute Trigger Go To Local Listener Active Listen Address Group Line Feed Local Lock Out My Listen Address My Talk Address Parallel Poll Configure Parallel Poll Unconfigure System Controller Selected Device Clear Serial Poll Disable Serial Poll
15. Section 3 IEEE 488 Bus Structure IEEE 488 Primer To Other Devices P nentes l Device 1 System Controller i H Able to Talk Listen and Control a Data Bus 5 Device 2 o well R Able to Talk Data Byte and Listen Transfer Control Device 3 Printer Only Able to Listen General Interface Management Device 4 Frequency Counter Only Able to Talk DIOI 8 DAV NRFD NDAC IFC ATN SRQ REN EOI Figure 3 1 3 3 Section 3 IEEE 488 Primer 3 3 SEND IT TO MY ADDRESS In the previous discussion the terms Addressed to Talk and Addressed to Listen were used These terms require some clarification The IEEE 488 standard permits up to 15 devices to be configured within one system Each of these devices must have a unique address to avoid confusion In a similar fashion every building in town has a unique address to prevent one home from receiving another home s mail Exactly how each device s address is set is specific to the product s manufacturer Some are set by DIP switches in hardware others by software Consult the manufacturer s instructions to determine how to set the address Addresses are sent with universal multiline commands from the Active Controller These commands include My Listen Address MLA My Talk Address MTA Talk Address Group TAG and Listen Address Group LAG 3 4 BUS MANAGEMENT LINES Five hardware lines on the GPIB are
16. als have the ability to assert SRQ A DMM might assert it when its measurement is complete if its input is overloaded or for any of an assortment of reasons A power supply might SRQ if its output has current limited This is a powerful bus feature that removes the burden from the System Controller to periodically inquire Are you done yet Instead the Controller says Do what I told you to do and let me know when you re done or Tell me when something is wrong Since SRQ is a single line command there is no way for the Controller to determine which device requested the service without additional information This information is provided by the multiline commandis for Serial Poll and Parallel Poll 3 10 Section 3 IEEE 488 Primer 3 8 1 Serial Poll Suppose the Controller receives a service request For this example let s assume there are several devices which could assert SRQ The Controller issues an SPE Serial Poll enable command to each device sequentially If any device responds with DIO7 asserted it indicates to the Controller that it was the device that asserted SRQ Often times the other bits will indicate why the device wanted service This Serial Polling sequence and any resulting action is under control of the software designer 3 8 2 Parallel Poll The Parallel Poll is another way the Controller can determine which device requested service It provides the who but not necessarily the why When bus devices are configu
17. capacitor between local Common and Earth Ground This configuration should be suitable for most applications If you wish to make any changes to this configuration follow the steps given below 2 3 Modifications The Isolator488 as shipped from the factory is configured for the typical use of the unit which is to isolate the instrument port from Earth ground and from Controller common The factory configuration should be used unless you have a significant variation in your application beyond galvanic isolation devices on the Instrument port If the factory configuration is not appropriate for your application the following procedures may be undertaken to modify the Isolator488 It is necessary to open the enclosure to make any of the following changes If yoou have any questions about a particular change please contact the applications department at 440 439 409 1 Disconnect the power cord from the AC line and from the Isolator488 Disconnect any IEEE cables prior to disassembly WARNING Never open the Isolator488 case while it is connected to the AC line Internal voltage potentials exist which could cause personal injury or death 2 Place the Isolator488 on a flat surface Remove the six screws on top of the case and remove the top cover Located to the right of the Controller Port IEEE 488 connector are locations for C16 RA and F2 Located to the right of the Instrument Port IEEE 488 connector are locations for C59 R5 and F3
18. devices on its Controller Port in addition to itself and the Isolator488 and up to 14 IEEE devices on the Instrument Port The Isolator488 has no address of its own and therefore will operate completely transparent to the system Be careful not to have two IEEE devices with the same address connected to either ports Failure to do so will result in the bus locking up when one of the devices is accessed 2 6 1 Bus Loading The IEEE 488 specification allows for a maximum of 15 bus loads The Isolator488 presents one bus load on each port Therefore an additional 14 devices can be placed on each the CONTROLLER and INSTRUMENT ports Because the IEEE controller presents one bus load a total of 27 instruments printers plotters and other peripherals can be accessed from a single IEEE controller 2 10 Section 2 2 6 2 Cabling Length Getting Started The IEEE 488 specification allows for cabling distance between bus devices of 2 meters approx 7 feet The total worst case distance from the two furthest devices is not allowed to exceed 20 meters approx 70 feet The addition of the Isolator488 does not increase this distance 2 6 3 Signal Line Direction The signal lines and their direction include Data Lines DIOI DIO7 Handshake Lines DAV NRFD NDAC Command Lines SRQ ATN EOI REN IFC Bidirectional Bidirectional Bidirectional Bidirectional To Controller Bus To Instrument Bus Bidirectional To Instrume
19. disconnect all cables from the Isolator488 and follow the steps below Isolator Fuse and Line Voltage Switch Locations WARNING LETHAL VOLTAGES MAY BE PRESENT S1 Power Connector 2 7 Section 2 Getting Started WARNING Never open the Isolator488 case while it is connected to the AC line Internal voltage potentials exist which could cause personal injury or death 1 Place the Isolator488 on a flat surface Remove the six screws on top of the case and remove the top cover Located next to the rear panel power connector is switch S2 and fuse F1 2 Insert the tip of a small screwdriver into the slot of the switch and move the switch to the left or right so that the desired line voltage selection appears on the switch Make note of the new setting for later reference CAUTION Use the 1 2 amp fuse FU 1 5 for 115 volt operation Use the 1 4 amp fuse FU 1 25 for 230 volt operation Failure to use the correct fuse could result in damage to the Isolator488 3 Replace the 1 2 amp fuse FU 1 5 for 115 volt operation with the 1 4 Amp fuse for 230 volt operation part number FU 1 25 that is included in the Isolator488 Accessory Kit 4 Carefully reassemble the unit WARNING The Isolator488 is intended for INDOOR USE ONLY Failure to observe this warning could result in equipment failure personal injury or death 2 8 Section 2 Getting Started 2 5 Hardware Installation Included with the Isolator
20. e for later reference The following changes may be made to the Instrument Port To add a soft ground between the Instrument Common and earth ground insert a 1 MQ 1 4 watt resistor in the location labelled R5 Insert a 0 01 uF 2kv ceramic capacitor in the location labelled C59 Solder these components in place from the solder side of the circuit board using rosin core solder The bottom panel or the Isolator488 will need to be removed in order to do this Make note of these changes for later reference 2 6 Section 2 Getting Started 2 To connect the Instrument Common to earth ground insert a 1 2 amp fuse in the fuse clips labelled F3 Make note of this change for later reference 3 To connect pin 12 shield of the Instrument Port to Instrument Common solder a bare jumper wire in the location labeled JPR2 Make note of this change for later reference After making any changes to the Isolator488 internal circuitry be sure to document your changes then carefully reassemble the unit 2 4 Line Voltage Selection The Isolator 488 is designed to accept either 105 to 125 volt or 210 to 250 volt 50 or 60 Hz AC power Each unit when shipped from the factory is labeled with its input voltage setting If this setting is not appropriate the internal voltage selection witch must be changed Failure to operate the Isolator488 from appropriate power source may result in damage to the unit To check or change the voltage selection switch
21. he data may be indicated by some special character such as carriage return The Active Controller also uses EOI to perform a Parallel Poll by simultaneously asserting EOI and ATN 3 4 5 Service Request SRQ When a device desires the immediate attention of the Active Controller it asserts SRQ It is then the Controllers responsibility to determine which device requested service This is accomplished with a Serial Poll or a Parallel Poll 3 5 Section 3 IEEE 488 Primer 3 5 HANDSHAKE LINES The GPIB uses three handshake lines in an I m ready Here s the data Ive got it sequence This handshake protocol assures reliable data transfer at the rate determined by the slowest Listener One line is controlled by the Talker while the other two are shared by all Active Listeners The handshake lines like the other IEEE 488 lines are active low 3 5 1 Data Valid DAV The DAV line is controlled by the Talker The Talker verifies that NDAC is asserted active low which indicates that all Listeners have accepted the previous data byte transferred The Talker then outputs data on the bus and waits until NRFD is unasserted high which indicates that all Addressed Listeners are ready to accept the information When NRFD and NDAC are in the proper state the Talker asserts DAV active low to indicate that the data on the bus is valid 3 5 2 Not Ready for Data NRFD This line is used by the Listeners to inform the Talker when they are
22. ipment we thoroughly test our products and 9001 review our documentation to assure the highest quality in all aspects In a spirit of continuous improvement IOtech welcomes your suggestions Isolator488 Instruction Manual Part No Isolator488 901 Revision 1 2 December 1991 IOtech Inc e 25971 Cannon Road e Cleveland Ohio 44146 e 440 439 4091 IMPORTANT READ THIS BEFORE INSTALLATION WARNING The enclosure of the Isolator488 Bus Isolator is internally connected to earth ground through the power cord However the shield of the IEEE 488 cables attached to the Isolator488 and signal ground pins may be at a high voltage with respect to earth ground Be sure to remove power from all devices in your system before handling IEEE 488 cables connected to the Isolator488 Failure to follow this warning may result in personal injury or death IOtech Inc e 25971 Cannon Road Cleveland Ohio 44146 440 439 4091 Section 1 1 1 1 2 1 3 14 Section 2 2 1 22 2 3 24 2 5 2 6 Section 3 3 1 3 2 3 3 3 4 3 5 3 6 3 7 2 6 1 2 6 2 2 6 3 2 6 4 2 6 5 3 4 3 4 2 3 4 3 3 4 4 3 4 3 5 1 3 5 2 3 5 3 Table of Contents INTRODUCTION General Description Available Accessories Specifications Abbreviations GETTING STARTED Inspection Configuration Modifications Line Voltage Selection Hardware Installations Operation BusLoading Cabling Length Signal Line Direction Parallel Polling Passing Control
23. n some devices are instructed to Unlisten is quite simple Suppose a college instructor is presenting the day s lesson Each student is told to raise their hand if the instructor has exceeded their ability to keep up while taking notes If a hand is raised the instructor stops his discussion to allow the slower students the time to catch up In this way the instructor is certain that each and every student receives all the information he is trying to present Since there are a lot of students in the classroom this exchange of information can be very slow In fact the rate of information transfer is no faster than the rate at which the slowest note taker can keep up The instructor though may have a message for one particular student The instructor tells the rest of the class to ignore this message Unlisten and tells it to that one student at a rate which he can understand This information transfer can then happen much quicker because it need not wait for the slowest student The GPIB transfers information in a similar way This method of data transfer is called handshaking More on this later For data transfer on the IEEE 488 the Active Controller must a Unlisten all devices to protect against eavesdroppers b Designate who will talk by addressing a device to talk c Designate all the devices who are to listen by addressing those devices to listen d Indicate to all devices that the data transfer can take place 3 2
24. nt Bus To Instrument Bus The majority of the command lines have their signal direction fixed This forces bus control from the CONTROLLER bus When Attention ATN is asserted the data lines talker handshake line DAV and the EOI line direction is forced from the CONTROLLER to the INSTRUMENT port The listener handshake lines NRFD and NDAC are forced from the INSTRUMENT to the CONTROLLER port The commands are sent through the Isolator488 to the INSTRUMENT port 2 11 Section 2 Getting Started When ATN is unasserted the Isolator488 asserts NDAC on both ports for a minimum of 200 nanoseconds while looking for an active talker If the talker is detected on the CONTROLLER port the NDAC lines are released and the data and handshake line directions remain unchanged If the active talker is detected on the INSTRUMENT port the data line direction is force to the CONTROLLER port and the handshake line directions are reversed The Isolator488 delays a minimum of 1200 nanoseconds to allow the data lines to settle before releasing the NDAC lines Once changed data transfers to 1 megabyte per second are possible 2 6 4 Parallel Polling During data transfer operations the data line transceivers are operated in tri state When a parallel poll is detected the CONTROLLER port transceiver is changed to open collector and the data line direction is forced from the Instrument Port to the Controller Port Parallel polling propagation delay th
25. peration is entirely transparent to the IEEE controller The IEEE standard defines 31 valid primary bus addresses Therefore no special software or bank switching is necessary to access the additional devices allowed by the Isolator488 The Isolator488 and has no effect on bus data transfer rates Two IEEE ports are provided One connects directly to the controller s IEEE bus the other to an additional 14 instruments printers plotters and specialized peripherals which may need to be optically isolated from the system controller 1 2 AVAILABLE ACCESSORIES Additional accessories that can be ordered for the Isolator488 include 123 0900 Instruction Manual CA 7 1 1 5 foot IEEE 488 cable CA 7 2 6 foot IEEE 488 cable CA 7 3 6 foot Shielded IEEE 488 cable CA 7 4 Reverse entry 6 foot IEEE 488 cable CN 20 Right Angle IEEE 488 adapter male and female CN 21 IEEE 488 connector Extender male and female CN 22 IEEE 488 multi tap bus strip four female connectors wired in parallel CN 23 IEEE 488 panel mount feed through connector male and female Section 1 1 3 SPECIFICATIONS PROPAGATION DELAYS Local to Remote Talker Data Lines Command Lines Remote to Local Talker ATN to Local Data ATN to Local DAV Data Lines Command Lines Parallel Poll Response SIGNAL LINE DIRECTIONS Data Lines DIOI DIO7 Handshake Lines DAV NRFD NDAC Command Lines SRQ ATN REN IFC ATN EOI CONNECTORS INDICATORS POWER ENVIRON
26. red for Parallel Poll they are assigned one bit on the data bus for their response By using the Status bit the logic level of the response can be programmed to allow logical OR AND conditions on one data line by more than one device When SRQ is asserted the Controller under user s software conducts a Parallel Poll The Controller must then analyze the eight bits of data received to determine the source of the request Once the source is determined a Serial Poll might be used to determine the why Of the two polling types the Serial Poll is the most popular due to its ability to determine the who and why In addition most devices support Serial Poll only 3 11 Service Information 4 1 FACTORY SERVICE IOtech maintains a factory service center in Cleveland Ohio If problems are encountered in using the Expander488 you should first telephone the factory Many problems can be resolved by discussing the problems with our applications department If the problem cannot be solved by this method you will be instructed as to the proper return procedure Appendix A Character Codes And IEEE Multiline Messages Ta ees a dee Pai 6 70 NUL SCG mi 01 1 e En pr pT a 1 561 7 71 SOH GTL dor a 02 2 Ce Ee GR ep e e a t 98 72 STX mi i p x rae la Pro ep ep 3 563 9 73 I wi Au ep 6 ep 52 we 68 S VS 100 Se P d ue 05 5 15 ep ep 53 m 5665 101 75 ea i a 00 0 PR Ka o D a d d a
27. rough the Isolator488 is typically 85 nanoseconds 2 6 5 Passing Control If another device is included in the system which can receive control it must be placed on the CONTROLLER port IEEE 488 control can not be passed through the Isolator488 2 12 Section 3 IEEE 488 Primer IEEE 48 Primer 3 1 HISTORY The IEEE 488 bus is an instrumentation communication bus adopted by the Institute of Electrical and Electronic Engineers in 1975 and revised in 1978 The Isolator488 conforms to this most recent revision designated IEEE 488 1978 Prior to the adoption of this standard most instrumentation manufacturers offered their own versions of computer interfaces This placed the burden of system hardware design on the end user If his application required the products of several different manufacturers then he might need to design several different hardware and software interfaces The popularity of the IEEE 488 interface sometimes called the General Purpose Interface Bus or GPIB is due to the total specification of the electrical and mechanical interface as well as the data transfer and control protocols The use of the IEEE 488 standard has moved the responsibility of the user from design of the interface to design of the high level software that is specific to the measurement application 3 2 GENERAL STRUCTURE The main purpose of the GPIB is to transfer information between two or more devices A device can either be an instrument or
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