Measurement Isolator488 User Manual

Isolator488
IEEE 488 Bus Isolator
USER’S MANUAL
IOtech, 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:
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.
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 i n ways other than described in t his 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
IOtech has maintained ISO 9001 certification since 1996. Prior to shipment, we thoroughly test our products and 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.
25971 Cannon Road Cleveland, Ohio 44146 (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. • 25971 Cannon Road • Cleveland, Ohio 44146 • (440) 439-4091

Table of Contents

Section 1 INTRODUCTION Page
1.1 General Description 1.1
1.2 Available Accessories 1.1
1.3 Specifications 1.2
1.4 Abbreviations 1.3
Section 2 GETTING STARTED Page
2.1 Inspection 2.1
2.2 Configuration 2.1
2.3 Modifications 2.4
2.4 Line Voltage Selection 2.7
2.5 Hardware Installations 2.9
2.6 Operation 2.10
2.6.1 BusLoading 2.11
2.6.2 Cabling Length 2.11
2.6.3 Signal Line Direction 2.12
2.6.4 Parallel Polling 2.13
2.6.5 Passing Control 2.13
Section 3 IEEE 488 Primer Page
3.1 History 3.1
3.2 General Structure 3.1
3.3 Send It To My Address 3.5
3.4 Bus Management Lines 3.5
3.4. Attention (ATN) 3.5
3.4.2 Interface Clear (IFC) 3.6
3.4.3 Remote Enable (REN) 3.6
3.4.4 End Or Identify (EOI) 3.6
3.4. Service Request (SRQ) 3.6
3.5 Handshake Lines 3.7
3.5.1 Data Valid (DAV) 3.7
3.5.2 Not Ready For Data (NRFD) 3.7
3.5.3 Not Data Accepted (NDAC) 3.7
3.6 Data Lines 3.8
3.7 Multiline Commands 3.8
Section 3 (cont.) Page
3.7.1 Go To Local (GTL) 3.8
3.7.2 Listen Address Group (LAG) 3.9
3.7.3 Unlisten (UNL) 3.9
3.7.4 Talk Address Group (TAG) 3.9
3.7.5 Untalk (UNT) 3.9
3.7.6 Local Lockout (LLO) 3.9
3.7.7 Device Clear (DCL) 3.9
3.7.8 Selected Device Clear (SDC) 3.10
3.7.9 Serial Poll Disable (SPD) 3.10
3.7.10 Serial Poll Enable (SPE) 3.10
3.7.11 Group Execute Trigger (GET) 3.10
3.7.12 Take Control (TCT) 3.10
3.7.13 Secondary Command Group (SCG) 3.10
3.7.14 Parallel Poll Configure (PPC) 3.11
3.7.15 Parallel Poll Unconfigure (PPU) 3.11
3.8 More On Service Requests 3.11
3.8.1 Serial Poll 3.12
3.8.2 Parallel Poll 3.12
Section 4 SERVICE INFORMATION Page
4.1 Factory Service 4.1
Appendix A
Character Codes and IEEE Multiline Messages
Section 1 Introduction
Introduction

1.1 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 operation 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 CA-7-1 CA-7-2 CA-7-3 CA-7-4 CN-20 CN-21 CN-22
CN-23
Instruction Manual
1.5 foot IEEE 488 cable 6 foot IEEE 488 cable 6 foot Shielded IEEE 488 cable Reverse entry 6 foot IEEE 488 cable Right Angle IEEE 488 adapter, male and female IEEE 488 connector Extender, male and female IEEE 488 multi-tap bus strip, four female connectors wired in parallel. IEEE 488 panel mount feed-through connector, male and female
1.1
Section 1 Introduction

1.3 SPECIFICATIONS

PROPAGATION DELAYS:
Local to Remote Talker
Data Lines 85 nS typ., 120 nS Max. Command Lines 90 nS typ., 125 nS Max.
Remote to Local Talker
/ATN to Local Data 355 nS typ., 475 nS Max. /ATN to Local DAV 155 nS typ., 2075 nS Max. Data Lines 85 nS typ., 120 nS Max. Command Lines 90 nS typ., 125 nS Max. Parallel Poll Response 140 nS typ., 205 nS Max.
SIGNAL LINE DIRECTIONS:
Data Lines:
DIO1 - DIO7 Bidirectional
Handshake Lines:
DAV, NRFD, NDAC Bidirectional
Command Lines:
SRQ, ATN, REN, IFC To Local Bus ATN To Remote Bus EOI Bidirectional
CONNECTORS: Two IEEE 488 connectors with metric studs INDICATORS: LED for Power POWER: 105-125V or 210-250V,50, 60 Hz; 20 VA MAX. ENVIRONMENT: 0 to 50 °C; 0 to 70% RH DIMENSIONS: 425 mm deep x 45 mm wide x 208 mm high.
(16.75 "x 1.75 "x 8.20 ") WEIGHT: 2.1 kg (4.6 lbs) CONTROLS: Power switch SUPPLIED ACCESSORIES: Power cable and manual ISOLATION: 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
5
500 Vac maximum, 10
Specifications are subject to change without notice.
V-Hz
1.2
Section 1 Introduction

1.4 Abbreviations

The following IEEE 488 abbreviations are used throughout this manual.
addr n IEEE bus address "n" ATN Attention line CA Controller Active CR Carriage Return data Data String DCL Device Clear GET Group Execute Trigger GTL Go To Local LA Listener Active LAG Listen Address Group LF Line Feed LLO Local Lock Out MLA My Listen Address MTA My Talk Address PPC Parallel Poll Configure PPU Parallel Poll Unconfigure SC System Controller SDC Selected Device Clear SPD Serial Poll Disable SPE Serial Poll Enable SRQ Service Request TA Talker Active TAD Talker Address TCT Take Control term Terminator UNL Unlisten UNT Untalk * Unasserted
1.3
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
123-0900
123-0800

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.
IEEE Bus Isolator Instruction Manual Accessory Kit ( includes power cable, fuse, and rack mounting hardware)
2.1
Section 2 Getting Started
Earth Ground The Ground terminal on the AC power cable. This is
internally connected to the chassis of the Isolator488.
Controller Port 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.
Instrument Port 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.
Controller Common 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.
Instrument 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. Controller Shield The Shield connection (Pin 12) on the Controller Port. Instrument Shield 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 MΩ resistor in parallel with a 0.01 µF 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) 439-4091.
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, R4, and F2. Located to the right of the Instrument Port IEEE 488 connector are locations for C59, R5, and F3. Refer to the following figure:
2.4
Section 2 Getting Started
C59
R5
F3
C50
Instrument Port
Common Components
C49
JPR2
TO INSTRUMENTS
C47 C48
Isolator488 Internal View
C16
R4
F2
Controller Port
Common Components
JPR1
TO CONTROLLER
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 change for later reference.
The following changes may be made to the Instrument Port:
1. To add a soft ground between the Instrument Common and earth ground, insert a 1 MΩ 1/4 watt resistor in the location labelled R5. Insert a 0.01 µF 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 disconnect all cables from the Isolator488 and follow the steps below.
Isolator Fuse and Line Voltage Switch Locations
WARNING :
S2
F1
Power Connector
115V
LETHAL VOLTAGES MAY BE PRESENT
S1
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 Isolator488 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
Enclosure
Top or Bottom View
Rack Ear
Screw
(2 per ear)
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
Top View
Enclosure
Bottom View
Top 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 co ntroller to command up to 13 IEEE dev ices on its Controller Po rt (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 co ntroller pres ents one b us load, a total of 27 instruments, printers, plotters and other peripherals can be accessed from a single IEEE controller.
2.10
Section 2 Getting Started

2.6.2 Cabling Length

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:
DIO1 - DIO7 Bidirectional
Handshake Lines:
DAV Bidirectional NRFD Bidirectional NDAC Bidirectional
Command Lines:
SRQ To Controller Bus ATN To Instrument Bus EOI Bidirectional REN To Instrument Bus IFC 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 through 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 488 Primer

3.1 HISTORY

The
IEEE 488
bus is an instrumentation co mmunication bus adopted
by the Institute of Electrical and Electronic Engineers in 1975 and revised in
1978. The
Isolator488
IEEE 488-1978
.
conforms to this most recent revision designated
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 t he products of several different manufacturers , then he might need to design several different hardware and software interfaces. The popularity of the
urpose Interface Bus or
P
IEEE 488
GPIB
interface (sometimes called the General
) 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 int erface to d esign of th e high level soft ware that is specific to the measureme nt appl ica ti on.

3.2 GENERAL STRUCTURE

The main purpose of the
GPIB
is to transfer information bet ween two or more devices. A device can either be an instrument or 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
Controller
The
.
System Controller
System Controller
is similar to a committee chairman. On a well
which is, at power on, the
Active
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 becomes the
Active Controller
.
GPIB
, this device
.
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 then referred to as an message are instructed to
Active Listener
Unlisten
Addressed to Listen
. This device is
. Devices which are to ignore the data
.
The reason 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 inst ructor has exceed ed their ability to keep up while taking notes. If a hand is raised, the inst ructor stops his discussio n 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.
GPIB
The
transfer is called
For data transfer on the
transfers information in a similar way. This method of data
handshaking
. More on this later.
IEEE 488
Active Controller
, the
must …
a) b) D esignate who wil l c) Designate all the devices who are to
devices to
Unlisten
all devices to protect against eavesdroppers.
listen
talk
.
addressing
by
a device to
listen
by
addressing
d) Indica te to all de vices that the da ta transfer can ta ke place.
3-2
talk
.
those
Section 3 IEEE 488 Primer
}
D
DAVN
N
IFCA
SRQR
EOIT
D
D
D
a
D
P
D
D
D
T
C
G
I
M
o Other Devices
evice 1
System Controller
Able to Talk,
Listen, and Control
ata Bus
evice 2
MM
Able to Talk
nd Listen
evice 3
rinter
Only Able to Listen
ata Byte ransfer ontrol
eneral
nterface
anagement
evice 4 Frequency Counter Only Able to Talk
IEEE 488 Bus Structure
Figure 3.1
IO1-8
RFD DAC
TN EN
3-3
Section 3 IEEE 488 Primer

3.3 SEND IT TO MY ADDRESS

In the previous discussion, the terms
Addressed to Listen
IEEE 488
The
were used. These terms require some clarification.
standard permits up to 15 devices to be configured
Addressed to Talk
and
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, oth ers by software. Consult the manufacturer's instructions to determine how to set the address.
Addresses are sent with
Active Controller My Talk Address Address Group
. These commands include
(MTA),
(LAG).
universal (multiline
My Listen Address
Talk Address Group
) commands from the
(MLA),
(TAG), and
Listen

3.4 BUS MANAGEMENT LINES

Five hardware lines on the
Signals on these lines are often referred to as
GPIB
are used for bus management.
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" (unasserte d).
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 is to be interpreted as a multiline command. If it is not, then that information is to be interpreted as data for the
Active Controller
is the only bus device that has control of this line.
3-4
Active Listener
s. The
Section 3 IEEE 488 Primer
3.4.2 Interface Cle ar (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 Listen Idle states (neither
IFC
command usually places the devices in the Talk and
Active Talker
Active Listener
nor
).
3.4.3 Remote Enable (REN)
When the
System Controller
sends the
devices will respond to remote operation. Generally, the
REN
command, bus
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)
EOI
The transfer. The device that is sending the data asserts transfer of the last data byte. The
line is used to signal the last byte of a multibyte data
EOI
during the
EOI
signal is not always necessary as the end of the data may be indicated by some special character such as carriage return.
Active Controller
The
simultaneously asserting
also uses
EOI
and
EOI
ATN
to perform a
.
Parallel Poll
by
3.4.5 Service Request (SRQ)
When a device desires the immediate attention of the
Controller
it asserts
SRQ
. It is then the Controller's responsibility to
Active
determine which device requested service. This is accomplished with a
Serial Poll
Parallel Poll
or a
.
3-5
Section 3 IEEE 488 Primer

3.5 HANDSHAKE LINES GPIB

The
uses three handshake lines in an "I'm ready - Here's the data
- I've 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) DAV
The
NDAC
is asserted (active low) which indicates that all Listeners have
line is controlled by the
accepted the previous data byte transferred. The data on the bus and waits until
Talker
NRFD
. The
Talker
Talker
verifies that
then outputs
is unasserted (high) which indicates that all Addressed Listeners are ready to accept the information. When asserts
DAV
( active low) to indicate that the da ta on the bus is va lid.
NRFD
and
NDAC
are in the proper state, the
Talker
3.5.2 Not Ready for Data (NRFD)
This line i s used by t he
Listeners
are ready to accept new data. The
to inform the
Talker
must wait for each
Talker
when they
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)
NDAC
The
indicates to the
line is also controlled by the
Talker
that each device addressed to listen has accepted
the information. Each device releases
NDAC
the
will not go high until the slowest Listener has accepted the
NDAC
Listeners
. This line
(high) at its own rate, but
data byte.
3-6
Section 3 IEEE 488 Primer
1st Data Byte 2nd Data Byte
DIO1-8
(composite)
DAV
Source
Valid Not
Valid
Valid
Not Valid
NRFD
Acceptor
NDAC
Acceptor
All
Ready
None
Accept
None
Ready
Accept
All
All
Ready
None
Accept
None Ready
All
Accept
IEEE Bus Handshaking

3.6 DATA LINES GPIB

The
transfer. These eight data lines use the convention of
provides eight data lines for a bit parallel/byte serial data
DIO1
through
DIO8
instead of the binary designation of D0 to D7. The data lines are bidirectional a nd are active low.

3.7 MULTILINE COMMANDS

Multiline
(bus) commands are sent by the
data bus with
ATN
asserted. These commands include addressing
Active Controller
over the
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 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 bit s are the ad dre ss of the device be in g told to li st en.
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 bit s are the addre ss of the dev ice be ing to ld to talk.
3.7.5 Untalk (UN T)
This command tells bus devices to Untalk. The same as Unaddressed to T alk. ($5F)
3.7.6 Local Lockout (LLO)
Issuing the
LLO
command prevents manual control of the
instrument's f unctions. ($ 11)
3.7.7 Device Clear (DCL)
This command causes all bus devices to be initialized to a pre­defined or power u p 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)
SPD
The
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 Exec ute Trigger (GET)
This command usually signals a group of devices to begin executing a triggered action. This allows actions of different devices to begin simul taneously. ($08)
3.7.12 Take Control (TCT)
This command passe s bus control responsibil ities from the current
Controller
to another de vice 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 im mediately follow a talk or listen address. ($60 to $7F)
3-9
Section 3 IEEE 488 Primer
3.7.14 Parallel P oll Configure (PPC)
This configures devices capable of performing a which data bit t hey are to assert in response to a
Parallel Poll
Parallel Poll
as to
. ($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 th e software designer h as 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 even t has occurred . It is
similar to an interrupt in a microprocessor ba sed system.
Most intelligent bus peripherals 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 "Are you done yet?". Instead, the
System Controller
Controller
says, "Do what I told you to
to periodically inquire,
do and let me know when you're done" or "Tell me when something is wrong."
Since
Controller
SRQ
is a single line command, there is no way for the
to determine which device requested the service without additional information. This information is provided by the multiline commands for
Serial Poll
Parallel Poll
and
.
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.
Serial Polling
This
sequence, and any resulting action, is under control
of the software designer.
3.8.2 Parallel Poll
Parallel Poll
The
is another way the
Controller
can determine which device requested service. It provides the who but not necessarily the why. When bus devices are configured for Parallel Poll, they are assigned one bit on the data bus for their res ponse. By using the Status bit, the logic level of the response can be programmed to allow logical OR/AND condit ions on one data line by more t han one device. When conducts a
Parallel Poll
SRQ
is asserted , the
. The
Controller
Controller
(under user's software)
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 ty pes, the
Serial Poll
is the most po pular due to i ts
ability to determine the who and why. In addition, most devices support
Serial Poll
only.
3-11
Service Information

4.1 FACTORY SERVICE IOtech

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.
maintains a factory service center in Cleveland, Ohio. If problems are
Appendix A Character Codes And IEEE Multiline Messages
E
FSG
R
U
0
1
2
345
6
7
89:
;
<
=>?
@
A
B
CDE
F
G
HIJ
K
L
MNO
P
Q
R
STU
V
W
XYZ
[
\
]^_
`
a
b
cde
f
g
hij
k
l
mno
$30$40$50$
$31$41$51$
$32$42$52$
$33$43$53$
$34$44$54$
$35$45$55$
$36$46$56$
$37$47$57$
$38$48$58$
$39$49$59$
$3A$4A$5A$
$3B$4B$5B$
$3C$4C$5C$
$3D$4D$5D$
$3E$4E$5E$
$3F$4F$5F$
1
17181
2
2
2
232425262
2
2
30U
0
01020
0
0
0
070809101
1
1
141
1
17181
2
2
2
232425262
2
2
30U
S
SCGSCGS
S
S
S
SCGSCGSCGSCGS
S
S
SCGS
4864809
495
5
525
5
656
6
686
7
818
8
848
8
979
9
1001
1
555
5
585
6
717
7
747
7
878
8
909
9
1031
1
1061
1
6162637778799394951091101
TAGS
T
S
$00 $10 $20
$01 $11 $21
GTL LLO
$02 $12 $22
$03 $13 $23
$04 $14 $24
SDC DCL
$05 $15 $25
PPC PPU
$06 $16 $26
$07 $17 $27
$08 $18 $28
GET SPE
$09 $19 $29
TCT SPD
$0A $1A $2A
$0B $1B $2B
$0C $1C $2C
NUL
SOH
STX
ETX
EOT
ENQ
ACK
BEL
BS
HT
LF
VT
10
11
12
0
1
2
3
4
5
6
7
8
9
16
DLE
00
17
DC1
01
18
DC2
02
19
DC3
03
20
DC4
04
21
NAK
05
22
SYN
06
23
ETB
07
24
CAN
08
25
M
09
26
SUB
10
27
ESC
11
28
FF
12
$0D $1D $2D
$0E $1E $2E
$0F $1F $2F
CR
SO
SI
13
14
15
29
S
13
30
S
14
31
S
15
ACG UCG
SP
#
$
%
&
*
+
!
"
'
(
)
,
-
.
/
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
LAG
6
9
0
1
2
7
8
9
NL
60 $70
6 112
p
0
6
CG
61 $71
SCG
113
q
SCG
0
6
62 $72
2
8
114
r
SCG
1
7
63 $73
3
9
115
s
3
9
CG
64 $74
SCG
116
t
4
3
0
9
CG
65 $75
5
01
SCG
117
u
5
4
1
0
CG
66 $76
6
02
SCG
118
v
6
2
CG
67 $77
SCG
119
w
SCG
6
2
68 $78
8
04
120
x
SCG
7
3
69 $79
9
05
121
y
SCG
6A $7A
122
z
SCG
9
5
6B $7B
1
07
123
{
1
0
7
6
CG
6C $7C
2
08
SCG
124
|
2
8
CG
6D $7D
SCG
125
}
3
9
CG
6E $7E
SCG
126
~
SCG
6F $7F
11
127
DEL
5
NT
CG
SCG
CG
ACG = Addressed Command Group UCG = Universal Command Group LAG = Listen Address Group
AG = Talk Address Group CG = Secondary Command Group
A.1
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