Keithley 1973 User manual

KEITH LEY
Model 1973/1972 IEEE-488 Interface
Instruction Manual
Contains Operating and Servicing Information
Publication Date: June 1991
Document Number: 1973-901-01 Rev. C

WARRANTY
Keithley Instruments, Inc. warrants this product to be free from defects in material and workmanship for a
period of 1 year from date of shipment.
Keithley Instruments, Inc. warrants the following items for 90 days from the date of shipment: probes, cables,
rechargeable batteries, diskettes, and documentation.
During the warranty period, we will, at our option, either repair or replace any product that proves to be de
fective.
To exercise this warranty, write or call your local Keithley representative, or contact Keithley headquarters in
Cleveland, Ohio. You wiU be given prompt assistance and return instructions. Send the product, transporta
tion prepaid, to the indicated service facility. Repairs will be made and the product returned, transportation
prepaid. Repaired or replaced products are warranted for the balance of the original warranty period, or at
least 90 days.
LIMITATION OF WARRANTY
This warranty does not apply to defects resulting from product modification without Keithley's express writ
ten consent, or misuse of any product or part. This warranty also does not apply to fuses, software, non-re
chargeable batteries, damage from battery leakage, or problems arising from normal wear or failure to follow
instructions.
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED, INCLUDING
ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. THE
REMEDIES PROVIDED HEREIN ARE BUYER'S SOLE AND EXCLUSIVE REMEDIES.
NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR
ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT
OF THE USE OF ITS INSTRUMENTS AND SOFTWARE EVEN IF KEHHLEY INSTRUMENTS, INC., HAS
BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES. SUCH EXCLUDED DAM
AGES SHALL INCLUDE, BUT ARE NOT LIMITED TO: COSTS OF REMOVAL AND INSTALLATION,
LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY.
KEITHLEY
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KEITH LEY
Model 1973/1972 IEEE-488 instruction Manual
Addendum
INTRODUCTION
This addendum to the Model 1973/1972 Instruction Manual is being provided in order to supply
you with the latest information in the least possible time. Please incorporate this change into the
manual immediately.
Add the following information to paragraph 4.3.8 SRQ Mask (M) and Status Byte Format:
A one-byte length variable should always be used to read the serial poll byte, regardless of the
IEEE-488 interface card or programming language. This is illustrated m the example that follows.
Programming Example — Routine to read the serial poll byte using a National GPIB interface
card with Borland Tiorbo Pascal v5.5:
{
Sample serial poU read routine for the Model 1973/1972
}
procedme read_serial_poll_byte;
var
serial_poll_byte : byte; (* Do not use word or integer type *)
(* Wait imtil reading done *)
begin
repeat
ibrsp(K197, serial_poll_byte); (* K197 came from ibfind *)
imtil serial_poll_byte <> 8;
end;
1973-901-02 Rev. C/8-91

Instruction Manual
Model 1973/1972
IEEE-488 Interface
Throughout the manual, references to the Model 197 also refer
to the Model 197A; references to the Models 1973 and 1972 also
refer to the Models 1973A and 1972A respectively.
©1991, Keithley Instruments, Inc.
All Rights Reserved
Instruments Division
Cleveland, Ohio, U. S. A.
Document Number: 1973-901-01

SPECIFICATIONS
IEEE OUTPUT (Options 1972 and 1973)
Accuracy:
The Model 197 accuracy specifications apply to the instrument if
either of the following two conditions are met:
1. Factory Installation—The Model 1972/3 is installed at the
factory.
2. Field Installation—When installed in the field, the instrument
must be calibrated and operated with the Model 1972/3.
If instrument is operated without recalibration after field installation
of Model 1972 or 1973, add to one year accuracy specifications:
DCV: add 0.004%
ACV: add 0.1%
OHMS: add 0.0075%
Warmup: 1 hour to rated accuracy.
Maximum Common-Mode Volt-Hertz Product: 1 X 10^
Output:
DATA
LOGGER
POINTER
I
ri
PREFIX
1
MANTISSA
51/2 DIGITS
001, NDGV ±1.23456 E±2
1
V ^
N=NORMAL
0 = OVERFLOW
Z = ZERO
DCV = DC VOLTS
ACV = AC VOLTS
DCA = DC CURRENT
ACA = AC CURRENT
OHM = RESISTANCE
DCD = DC dB
ACD = AC dB
EXPONENT
Time from Trigger to Reading Done:
Tl, T3: 500ms (650ms in Ohms) typical
T5: 400ms (550ms in Ohms) typical
Address Modes: Talk Only, Addressable
ANALOG/IEEE OUTPUT (Model 1972 Option)
Accuracy: ±(0.25% of displayed reading ±2mV).
In XIOOO, 2mV output = 0.2 displayed counts.
Response Time: Follows displayed conversion rate.
Level: IV = 100,000 counts on XI gain.
IV = 100 counts on XlOOO gain.
Maximum output voltage = 4V.
Output Resistance: lOOOfi.
Isolation: 500V peak, input LO to output LO.
30V peak, output LO to earth ground.
IEEE-488 BUS IMPLEMENTATION
Multiline Commands: DCL, SDC, GET, GTL, UNT, UNL, SPE,
SPD.
Uniline Commands: IFC, REN, EOI, SRQ, ATN.
Interface Functions: SHl, AHl, T5, TEO, L4, LEO, SRI, RLO,
PPO, DCl, DTI, CO, El.
Programmable Parameters: Range, REL, dB, EOI, Trigger, Calibra
tion, SRQ, Status, Data Format, Terminator, Data Logger
Retrieval.
Device-Dependent Commands:
dB:
DO = dB off
Dl = dB on
Range: (Amps function not programmable but status word reflects
the codes shown.)
Volts
Ohms
Amps
RO
Auto Auto
Rl
200m
200 200/i
R2 2 2k
2m
R3 20
20k 20m
R4 200 200k
200m
R5 2000 2M, 20M, 200M
2000m
R6
lOA
Relative:
ZO =
Z1 =
Trigger:
TO =
Tl =
T2 =
T3 =
T4 =
T5 =
REL off
REL on
Continuous on Talk
One-shot on Talk
Continuous on GET
One-shot on GET
Continuous on X
One-shot on X
Execute:
X = Execute other device-dependent commands.
EOI:
KO = EOI Enabled
K1 = EOI Disable
Status Word:
UO = Output status word.
Data Format:
GO = Readings and status word with prefix.
G1 = Readings and status word without prefix.
Data Logger:
BO = Sends Display Readings
Bl = Sends stored Readings (Analog output reflects
recalled reading)
SRQ:
Mo = Clear SRQ Data Mask
Ml = Reading Overflow
M8 = Reading Done
M9 = Reading Done or Reading Overflow
M16 = Busy
M17 = Busy or Reading Overflow
M24 = Busy or Reading Done
M25 = Busy, Reading Done or Reading Overflow
Clear SRQ Error Mask
IDDCO
M34 = IDDC
M35 = IDDC or IDDCO
M36 = Not in Remote
M37 = Not in Remote or IDDCO
M38 = Not in Remote or IDDC
M39 = Not in Remote, IDDC or IDDCO
Digital Calibration:
V ± n.nnnnnE ± nn = enter calibration value.
Store:
LO = Store calibration constants.
Terminator:
Y(ASCII) = ASCII Character
Y(LF) = CR LF
Y(CR) = LF CR
Y(DEL) = None Specifications subject to change without notice.
M32
M33

TABLE OF CONTENTS
SECTION 1-GENERAL INFORMATION
1.1 Introduction
1.2 Interface Features
1.3 Warranty Information
1.4 Manual Addenda
1.5 Safety Symbols and Terms
1.6 Using the Instruction Manual
1.7 Specifications
1.8 Unpacking and Inspection
2
-2
SECTION 2-AN OVERVIEW OF THE IEEE-488 BUS
2.1 Introduction 2-1
2.2 Bus Description 2-1
2.3 IEEE-488 Bus Lines 2-1
2.3.1 Bus Management Lines 2-1
2.3.2 Handshake Lines 2-2
2.3.3 Data Lines 2-3
2.4 Bus Commands 2-3
2.4.1 Uniline Commands 2-3
2.4.2 Universal Commands 2-3
2.4.3 Addressed Commands 2-4
2.4.4 Unaddressed Commands 2-4
2.4.5 Device-Dependent Commands 2-4
2.5 Command Codes 2-4
2.6 Command Sequences 2-4
2.6.1 Addressed Command Sequence 2-6
2.6.2 Universal Command Sequence 2-6
2.6.3 Device-Dependent Command Sequence 2-6
SECTION 3-SYSTEM CONFIGURATION
3.1 Introduction 3-1
3.2 Hardware Consideration 3-1
3.2.1 Typical Systems 3-1
3.2.2 Bus Connections 3-1
3.2.3 Primary Address Selection 3-3
3.3 Software Considerations 3-4
3.3.1 Controller Interface Routines 3-4
3.3.2 HP-85 BASIC Statements 3-4
3.3.3 Interface Functions Codes 3-5
3.3.4 Interface Commands 3-6

SECTION 4-OPERATION
4.1 Introduction
4.2 General Bus Commands
4.2.1 REN (Remote Enable)
4.2.2 IFC (Interface Clear)
4.2.3 CTL (Co To Local) 4-2
4.2.4 DCL (Device Clear) 4-2
4.2.5 SDC (Selective Device Clear) 4-2
4.2.6 Serial Polling (SPE, SPD) 4-3
4.3 Device-dependent Command Programming 4-3
4.3.1 Execute (X) 4-4
4.3.2 dB(D) f4
4.3.3 Range (R) 4-4
4.3.4 Relative (Z) 4-6
4.3.5 Triggering (T) 4-6
4.3.6 EOl(K)
4.3.7 Status Word (U) 4-7
4.3.8 SRQ Mode (M) and Status Byte Format 4-7
4.3.9 Data Format 4-10
4.3.10 Prefix (C) 4-10
4 3 11 Programmable Terminator (Y) 4-11
4.3.12 Buffer (B) 4-11
4.3.13 Digital Calibrator (V) and Storage (L) 4-12
4.4 Talk Only Operation 4-12
SECTION 5-ANALOG OUTPUT (Model 1972 only)
5.1 Introduction ^"4
5.2 Using Analog Output ■^"4
5.3 Output Resistance
5.4 XIOOO Mode Resolution and Accuracy 5-3
SECTION 6-THEORY OF OPERATION
6.1 Introduction ^"4
6.2 Circuit Description ^"4
6.2.1 Power Supply ^'4
6.2.2 Digital Circuitry ^"2
6.2.3 Analog Output (Model 1972 only) 5-2
SECTION 7-MAINTENANCE
7.1 Introduction ^"4
7.2 Installation ^'4
7.3 Calibration (Model 1972 only) 7-1
7.3.1 Warm Up 7-1
7.3.2 Recommended Calibration Equipment 7-3
7.3.3 Environmental Conditions 7-3
7.3.4 Calibration 7-3
7.4 Special Handling of Static Sensitive Devices 7-3
7.5 Troubleshooting 7-3

SECTION 8-REPLACEABLE PARTS
8.1 Introduction 8-1
8.2 Replaceable Parts 8-1
8.3 Ordering Information 8-1
8.4 Factory Service 8-1
8.5 Schematic Diagrams and Component Location Drawings 8-1
III

5-2
5-3
5-4
7-1
7-2
7-3
8-1
8-2
LIST OF TABLES
Table
Title Page
2-1 IEEE-488 Bus Command Summary 2-6
2-2 Hexadecimal and Decimal Command Codes 2-6
2-3 Typical Addressed Command Sequence 2-7
2-4 Typical Device-Dependent Command Sequence 2-7
3-1 IEEE Contact Designation 2-2
3-2 Primary Address Switch Positions 2-4
3-3 HP-85 IEEE-488 BASIC Statement 2-5
3-4 Interface Function Codes 2-6
3-5 IEEE Command Groups 2-6
4-1 General Bus Commands ^'2
4-2 Default Values (Status Upon Power Up or After SDC or DCL) 4-3
4-3 Device-Dependent Command Summary 4-5
4-4 Range Commands
4-5 SRQ Mask Commands
4-6 Status Byte and Mask Interpretation 4-10
5-1 Analog Output Parameters (V) 2-2
Analog Output Parameters (Q) 2-2
Analog Output Parameters (I) 2-2
Analog Output Parameters (dB) 2-3
Static Sensitive Devices 2-3
Model 1972 Interface Checks 2-4
Model 1973 Interface Checks 2-5
Model 1973 Parts List 2'2
Model 1972 Parts List 2*2
IV

LIST OF ILLUSTRATIONS
Figure Title Page
2-1 IEEE Bus Configuration 2-2
2-2 Handshake Sequence 2-3
2-3 Command Codes 2-5
3-1 System Types 3-1
3-2 IEEE-488 Connector 3-1
3-3 IEEE-488 Connections 3-2
3-4 Contact Assignments 3-2
3-5 Rear Panel of Model 197 Showing IEEE Connections and Switches 3-3
3-6 Typical IEEE-488 Bus Driver (One of 16) 3-3
3-7 Primary Address Switches (Address 20 Shown) 3-4
4-1 General Format for UO Command 4-8
4-2 Status Byte Format 4-10
4-3 Data Format 4-10
5-1 Analog Output Connections 5-1
5-2 XIOOO Analog Output 5-2
6-1 Simplified Block Diagram 6-1
6-2 Memory Map 6-2
6-3 XI and XlOOO Gains i 6-2
7-1 Model 1973 Installation 7-1
8-1 Model 1973, Component Location Drawing, Dwg. No. 1973-100 8-5
8-2 Model 1972, Component Location Drawing, Dwg. No. 1972-100 8-7
8-3 Model 1973, Schematic Diagram, Dwg. No. 1973-106 8-9
8-4 Model 1972, Schematic Diagram, Dwg. No. 1972-106 8-11
v/vi

SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
The Model 1973 is an IEEE-488 interface for the Model 197
Autoranging Microvolt DMM. This interface adds extra
versatility to the Model 197 by allowing the transmission of
data and commands over the IEEE-488 bus. The interface
provides all the necessary logic to interface the Model 197 to
the bus using standard IEEE-488-1973 protocol.
The Model 1972 is an IEEE-488 interface that is very similar
to the Model 1973. In fact, the only difference between the
two interfaces is that the Model 1972 includes an Analog
Output and the Model 1973 does not.
Since the only difference between the two interface is the
analog output, the Model 1973 is referred to throughout the
manual. Section 5 and 6 contain information concerning the
analog output of the Model 1972. All the rest of the informa
tion pertaining the Model 1973 also relates the Model 1972.
The analog output specifications precede the Table of Con
tents.
The Model 1973/1972 IEEE-488 Instruction Manual covers
the following IEEE-488 interface options:
• Model 1973 IEEE-488 Interface (for the Model 197)
• Model 1973A IEEE-488 Interface (for the Model 197A)
• Model 1972 IEEE-488 Interface (for the Model 197)
• Model 1972A IEEE-488 Interface (for the Model 197A)
1.2 INTERFACE FEATURES
Important IEEE-488 interface features include:
• With the Model 1973 installed, the Model 197 is able to
communicate with other instrumentation using the same
IEEE-488-1978 standards.
• Standard IEEE coimector that provides easy connection
to the IEEE-488 bus.
• The primary address of the Model 197/1973 may be eas
ily changed by using the five address switches on the rear
panel of the instrument.
All Model 197 operation is supported by IEEE program
ming. In addition, numerous other IEEE commands add
operating features not available from the front panel.
1.3 WARRANTY INFORMATION
Warranty information may be found on the inside front
cover of this manual. Should it become necessary to exercise
the warranty, contact your Keithley representative or the
factory to determine the proper course of action. Keithley
Instruments Inc. maintains service facilities in the United
States, United Kingdom and throughout Europe. Ad
dresses for these facilities may be foimd inside the front
cover of this manual. Information concerning the applica
tion, operation or service of your instrument may be di
rected to the applications engineer at any of these locations.
1.4 MANUAL ADDENDA
Information concerning improvements or changes to the in
strument which occur after the printing of this manual may
be fovmd on an addendum included with this manual. Be
sure to review these changes before attempting to program
the instrument.
1.5 SAFETY SYMBOLS AND TERMS
The following safety symbols and terms are used in this
manual and may be fotmd on the instrument.
lA,
The symbol AdA on the instrument indicates that the user
should refer to the operating instructions.
The symbol If on the instrument indicates that a potential
of lOOOV or more may be present on the terminals. Standard
safety precautions should be observed when such danger
ous voltage levels are encountered.
Information associated with the WARNING heading ex
plains dangers that could result in personal injury or death.
1-1

Information following the CAUTION heading explains
hazards that could damage the instrument.
1.6 USING THE INSTRUCTION MANUAL
This manual contains all information necessary to connect
the Model 1973 to the lEEE-488 bus and program the instru
ment from a separate bus controller.
The manual is divided into the following sections;
1. Section 2 contains a general description of the lEEE-488
bus and its commands.
2. Section 3 contains information necessary to connect the
instrument to the bus and set the primary address.
3. The bulk of the programming information may be
found in section 4. General bus command as well as
commands unique to the Model 1973 are covered in de
tail.
4. Section 5 contains maintenance information such as in
stallation and troubleshooting.
5. Section 6 contains replaceable parts information.
1.7 SPECIFICATIONS
A complete list of IEEE specifications can be found preced
ing this section.
1.8 UNPACKING AND INSPECTION
The Model 1973 interface was carefully inspected both me
chanically and electrically before shipment. Upon receiving
the Model 1973, carefully impack all items and check for any
obvious physical damage that may have occurred during
shipment. Report any damage to the shipping agent imme
diately. Retain and use the original packing material in case
reshipment is necessary. The following items are shipped
with every Model 1973 order:
Model 1973 lEEE-488 Interface
Hardware necessary for installation.
Model 1973 Instruction Manual
Additional accessories as ordered.
If an additional manual is required, order the manual pack
age (Keithley part number 1973-901-00). The manual pack
age includes an instruction manual and all pertinent ad
denda.
1-2

SECTION 2
AN OVERVIEW OF THE IEEE-488 BUS
2.1 INTRODUCTION
The IEEE bus is an instrumentation data bus adopted by the
IEEE (Institute of Electrical and Electronic Engineers) in 1975
and given the lEEE-488 designation. The most recent revision
of bus standards was made in 1978; hence the complete des
cription for current bus standards is the lEEE-488-1978
designation.
sent up to the hardware constraints of the bus. Generally, the
bus is limited to 15 devices, but this number may be reduced
if higher than normal data transfer rates are required or if
longer than normal cables are used.
Several devices may be connected to listen at once, but only
one device may be a talker at any given time. Otherwise,
communications would be garbled much like trying to pick
out a single conversation in a large crowd.
This section gives a brief description of the general bus struc
ture along with an outline of bus commands. The information
presented here is not intended to be an in-depth description of
what is truly a very complex set of standards. More complete
information on the IEEE-488 bus which is frequently referred
to as the General Purpose Interface Bus (GPIB) is available
from the IEEE and a variety of other sources.
Before a device can be a talker or a listener it must be ap
propriately addressed. Devices are selected on the basis of
their primary address; the addressed device is sent a talk or
listen command derived from its primary address. Normally,
each device on the bus has a unique address so that each may
be addressed individually.
2.2 BUS DESCRIPTION
The IEEE-488 bus was designed as a parallel data transfer
medium to optimize data transfer without using an excessive
number of bus lines. In keeping with goal, the bus has only
eight data lines that are for both data and some commands.
Five bus management lines and three handshake lines round
out the complement of signal lines. Since the bus is of parallel
design, all devices connected to the bus have the same infor
mation available simultaneously. Exactly what is done with
the information by each device depends on many factors, in
cluding device capabilties.
A typical bus configuration for controlled operation is shown
in Figure 2-1. The typical system shown will have one con
troller and one or more instruments to which the commands
are given and in most cases from which the data is received.
Generally, there are three categories that describe device
operation. These designations include: controller; talker and
listener.
The controller does what its name implies; it controls other
devices on the bus. A talker sends data; while a listener
receives data. Depending on the instrument, a particular
device may be a talker only or both a talker and a listener.
Any given system can have only one controller (control may
be passed to an appropriate device through a special com
mand), but any number of talkers and listeners may be pre-
Once each device is addressed to talk or listen, appropriate
bus transactions are set to take place. For example, if an in
strument is addressed to talk, it will usually place its data on
the bus one byte at a time. The listening device will read this
information and the appropriate software can then be used to
channel the information to the desired location.
2.3 IEEE-488 BUS LINES
The signal lines on the IEEE-488 bus lines are grouped into
three general categories. The data lines handle bus informa
tion, while the handshake and bus management lines ensure
that proper data transfer and bus operation take place. Each
of these bus lines is active low so that approximately zero
volts is a logic one. The following paragraphs describe the
purpose of these lines which are shown in Figure 2-1.
2.3.1 Bus Management Lines
The bus management group is made up of five signal lines
that help ensure an orderly transfer of data. These lines are
used to send the uniline commands described in paragraph
2.4.
ATN (Attention)—The ATN line is one of the more impor
tant management lines. The state of the ATN line determines
whether controller information on the data bus is to be con
sidered data or a multiline command as described in
paragraph 2.4.
2-1

IFC (Interface Clear)—Setting the IFC line true (low) causes
the bus to go to a known state by sending the IFC command.
REN (Remote Enable)—Setting the REN line low sends the
REN command. This sets up instruments on the bus for re
mote operation.
EOI (End Or Identify)—The EOI line is used to send the EOI
command that usually terminates a multi-byte transfer se
quence.
SRQ (Serive Request)—The SRQ line is set low by a device
when it requires service from the controller.
2.3.2 Handshake Lines
The bus uses three handshake lines that operate in an in
terlocked sequence. This method ensures reliable data
transfer regardless of the transfer rate. Generally, data
transfer occurs at a rate determined by the slowest active
device on the bus.
One of the handshake lines is controlled by the data source,
while the remaining two lines are controlled by the accepting
device. The three bus handshake lines are:
TO OTHER DEVICES
DEVICE 1
ABLE TO
TALK, LISTEN
AND CONTROI
(COMPUTER)
DEVICE 2
ABLE TO
TALK AND
LISTEN
DEVICE 3
ONLY ABLE
TO LISTEN
(PRINTER)
DEVICE 4
ONLY ABLE
TO TALK
(DMM)
DATA BUS
DATA BYTE
TRANSFER
CONTROL
GENERAL
INTERFACE
MANAGEMENT
D101...8 DATA (8 LINES)
DAV )
NRFD [handshake
NDAC;
■ BUS MANAGEMENT
DAV (Data Valid)—The source controls the state of the DAV
line.
NRFD (Not Ready For Data)—The acceptor controls the
states of the NRFD line.
NDAC (Not Data Accepted)—The acceptor controls the state
of the NDAC line.
The complete handshake sequence for one data byte is shown
in Figure 2-2. Once data is on the bus, the source checks to see
that NRFD is high, indicating that all devices on the bus are
ready for data. At the same time NDAC should be low from
the previous byte transfer. If these conditions are not met, the
source must then wait until the NRFD and NDAC lines have
the correct status. If the source is a controller, NRFD and
NDAC must remain stable for at least lOOnsec after ATN is
low. Because of the possibility of bus hang up, some con
trollers have time out routines to display error messages if the
handshake sequence stops for any reason.
Once the NRFD and NDAC lines are properly set, the source
sets the DAV line low, indicating that data on the bus is now
valid. The NRFD line then goes low; the NDAC line goes high
once all the devices on the bus have accepted the data. Each
device will release the NDAC line at its own rate, but the
NDAC line will not go high until the slowest device has ac
cepted the data byte.
After the NDAC line goes high, the source then sets the DAV
line high to indicate that the data on the bus is no longer
valid. At this point, the NDAC line returns to its low state.
Finally, the NRFD line is released by each of the devices at
their own rate, until the NRFD line finally goes high when the
slowest device is ready and the bus is set to repeat the se
quence with the next data byte.
Figure 2-1. IEEE Bus Configuration
2-2

2.3.3 Data Lines 2.4.1 Unillne Commands
The IEEE-488 bus uses the eight data lines that allow data to
be transmitted and received in a bit-parallel, byte-serial man
ner. The eight lines use the convention DlOl through DI08 in
stead of the more common DO through D7 binary ter
minology. The data lines are bidirectional and, as with the re
maining bus signal lines, low is true.
Uniline commands are sent by setting the associated bus line
low. The ATN, IFC and REN commands are asserted only by
the system controller. The SRQ command is sent by either the
controller or an external device depending on the direction of
data transfer. The following is a brief description of each
command.
2.4 BUS COMMANDS
While the hardware aspect of the bus is essential, the interface
would be essentially worthless without the appropriate com
mands to control communications between the various in
struments on the bus. This section briefly describes the pur
pose of the bus commands, which are grouped into the three
general categories:
Uniline Commands-
low.
-Sent by setting the associated bus line
Multiline Commands—General bus commands which are
sent over the data lines with the ATN line low.
Device-dependent Commands—Special commands that de
pend on device configuration; sent over the data lines with
ATN high.
DATA
X
DAV
X
SOURCE
SOURCE
VALID
NRFD
ACCEPTOR
NDAC
ACCEPTOR
DATA
TRANSFER
BEGIN
DATA
TRANSFER
END
Figure 2-2. Handshake Sequence
REN (Remote Enable)—When the controller sends the REN
command, the instrument will be set up for remote operation.
Generally, the REN command should be sent before attempt
ing to program the instruments over the bus.
EOI (End Or Identify)—The EOI command is used to
positively identify the last byte in a multi-byte transfer se
quence. This allows variable length data words to be
transmitted easily.
IFC (Interface Clear)—The IFC command is sent to clear the
bus and set devices to a known state. Although device con
figurations differ, the IFC command usually places in
struments in the talk and listen idle states.
ATN (Attention)—The controller sets ATN true while
transmitting addresses or multiline commands. Device-
dependent commands are sent with the ATN line high (false).
SRQ (Service Request)—The SRQ command is asserted by an
external device when it requires service from the controller. If
more than one device is present, a serial polling sequence, as
described in Section 4 must be used to determine which device
has requested service.
2.4.2 Universal Commands
Universal commands are multiline commands that require no
addressing. All instrumentation equipped to implement the
command will do simultaneously when the command is
transmitted over the bus. As with all multiline commands,
the universal commands are sent over the data line with ATN
low.
LLO (Local Lockout)—The LLO command is used to lock out
front panel controls on devices so equipped.
DCL (Device Clear)—After a DCL is sent, instrumentation
equipped to implement the commands will revert to a known
state. Usually, instruments return to their power-up condi
tions.
SPE (Serial Poll Enable)—The SPE command is the first step
in the serial polling sequence. The serial polling sequence is
used to determine which instrument has requested service
with the SRQ command.
2-3

SPD (Serial Poll Disable)—The SPD command is sent by the
controller to remove all instrumentation from the serial poll
mode.
2.4.3 Addressed Commands
Addressed commands are multiline commands that must be
preceded by a listen command before the instrument will re
spond. The listen command is derived from the device's
primary address. Only the addressed device will respond to
each of these commands:
SDC (Selective Device Clear)—The SDC command performs
essentially the same function as the DCL command. The dif
ference is with the SDC command only the addressed device
will respond. The addressed instrument usually returns to its
default conditions when the SDC command is sent.
GTL (Go To Local)—The GTL command is used to remove
instruments from the remote mode of operation. Also, front
panel operation will usually be restored if the LLO command
was previously sent.
GET (Group Execute Trigger)—The GET command is used to
trigger devices to perform a specific action that depends on
device configuration. Although GET is considered to be an
addressed command, many devices respond to GET without
being addressed.
2.4.4 Unaddressed Commands
2.5 COMMAND CODES
Each multiline command is given a unique code that is
transmitted over the bus as 7 bit ASCII data. This section
briefly explains the code groups which are summarized in
Figure 2-3. Every command is sent with ATN low.
Addressed Command Group (ACG)—Addressed commands
are listed in column 0(B) in Figure 2-3. Column 0(A) lists the
corresponding ASCII codes.
Universal Command Group (UCG)—Columns 1(A) and 1(B)
list the Universal commands and the corresponding ASCII
codes.
Listen Address Group (LAG)—Columns 2(A) and 3(A) list
the ASCII codes corresponding to the primary address listed
in columns 2(B) and 3(B). For example, if the primary address
is sent to 12, the LAG byte will correspond to an ASCI1(,)
command.
Talk Address Group (TAG)—TAG primary address values
and the corresponding ASCII characters are listed in columns
4(A) through 5(B).
The preceding address groups are combined together to form
the Primary Command Group (PCG). The bus also has
another group of commands, called the Secondary Command
Group (SCG). These are listed in Figure 2-3 for informational
purposes only; the Model 1973 does not respond to these
commands, but other devices may have secondary addressing
capability.
The two unaddressed commands are used by the conroller to
remove all talkers and listeners from the bus simultaneously.
ATN is low when these mutliline commands are asserted.
UNL (Unlisten)—All listeners are removed from the bus at
once when the UNL command is placed on the bus.
UNT (Untalk)—The controller sends the UNT command to
clear the bus of any talkers.
2.4.5 Device-Dependent Commands
NOTE
Commands are normally transmitted with the 7
bit code listed in Figure 2-3. For most devices,
the condition of Dy (DI08) is unimportant, as
shown by the "Don't Care" indication in the
table. Some devices, however, may require that
Dy assumes a specific logic state before the com
mands are recognized.
Hexadecimal and decimal values for each of the commands or
command groups are listed in Table 2-2. Each value in the
table assumes that Dy is set to 0.
The meaning of the device-dependent commands is deter
mined by instrument configuration. Generally, these com
mands are sent as one or more ASCII characters that tell the
device to perform a specific function. For example, Zl is sent
to place the instrument in the relative mode. For complete in
formation on using these commands with the Model 1973,
refer to Section 4. The IEEE-488 bus treats device-dependent
commands as data with the ATN line high (false) when the
commands are transmitted.
2.6 COMMAND SEQUENCES
The proper command sequence must be sent by the controller
before an instrument will respond as intended. The universal
commands such as LLO and DCL, require only that ATN be
set low before the command is sent. Other commands require
that the device be addressed to listen first. This section briefly
describes the bus sequence for several types of commands.
2-4

VD?
\D6
X
0
0
0 COMMAND
X
0
0
1
COMMAND
X
0
1
0
PRIMARY
ADDRESS
X
0
1
1
PRIMARY
ADDRESS
X
1
0
PRIMARY
ADDRESS
X
1
0 PRIMARY
ADDRESS
X
1
1
0
X
1
1
1
D3
D2
Di
[ 0
Q
COLUMN -
ROW.
0 lAl
0 (Bi
1 lAi 1 (01
2 !Ai
2 iB)
3 lA)
3 (Bi
4 (A) 4 iBi 5 (A) 5 (BI 6 (A1
6 (81
7 lA) 7 (B)
0 0 0 0
0 NUL DLE SP 0 0
16
@
0
P
16
P
0 0 0
11
SOH
GTL DC1 LLO
11 17 A
1
0
17
a
q
0 0
1
0 2 STX DC2 22
18
B
2 R 18 b
0 0
11
3
ETX DC3
t
3
3 19
C S 19 c
s
0
t
0 4 EOT
SDC
DC4
OCL
$
44
20 D
4 T
20
d
0
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0 5
ENQ
PPC*
NAK
PPU*
% 5
5
21
E
5 U
21
e
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0
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6
ACK
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&
6
6
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6
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22
f
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7
BEL ETB
7 7
23
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7
w 23
9
vs.
0 8
BS
GET
CAN SPE
8 8
24 H
8
X
24
h
x
9
HT
TCT*
EM
SPD
9
9
28
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9
Y 25 V
10 LF
SUB
10 26
J
10
z 26
z
1
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ESC
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27
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i 27
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FF
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13
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m
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0
14
SO RS
14
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30 N
14
r\
30
n
-
1
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15 SI US
/ 15
UNL 0 15
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UNT
0
DEL
ADDRESSED
COMMAND
GROUP
'ACGi
UNIVERSAL
COMMAND
GROUP
'UCGl
LISTEN
ADDRESS
GROUP
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TALK
ADDRESS
GROUP
iTAG)
V.
•PPC iParallel Poll Configure) PPU (Parallel Poll U'K.onfigurel . and
TCT (Take Control: no! implemented by Model 2243
DI01 D;
Don't Care
PRIMARY
COMMAND
GROUP
iPCGi
y V
"V"
SECONDARY
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(SDC)
y
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I
CJI
Figure 2-3. Command Codes

Table 2-1. iEEE-488 Bus Command Summary
State of
Command Type
Command
ATN Line* Comments
Uniline
REN (Remote Enable)
X Set up for remote operation.
EOl (End Or Identify)
X
Sent by setting EOl low.
IPG (Interface Clear)
X
Clear Interface.
ATN (Attention)
Low
Defines data bus contents.
SRQ (Service Request)
X
Controlled by external device.
Multiline
Universal
DCL (Device Clear)
Low
Returns device to default conditions.
SPE (Serial Poll Enable)
Low
Enables serial polling.
SPD (Serial Poll Disable)
Low
Disables serial polling.
Addressed SDC (Selective Device Clear)
Low Returns unit to default conditions.
GTL (Go To Local)
Low Returns to local control.
GET (Group Execute Trigger)
Low Triggers device for reading.
Unaddressed
UNL (Unlisten)
Low
Removes all listeners from bus.
UNT (Untalk)
Low
Removes all talkers from bus.
Device-dependent**
High
Programs Model 197 for various modes.
•X = Don't Care
*See paragraph 4.3 for complete description.
Table 2-2. Hexadecimal and Decimal Command
Codes
Command
Hex Value*
Decimal Value
GTL
01
1
SDC
04
4
GET
08
8
DCL
14 20
SPE
18
24
SPD
19
25
LAG
20-3F
32-63
TAG
40-5F
64-95
UNL
3F
63
UNT
5F
95
^Values shown with = 0.
2.6.1 Addressed Command Sequence
Before a device will respond to one of these commands, it
must receive a LAG command derived from its primary ad
dress. Table 2-3 shows a typical sequence for the SDC com
mand. The LAG command assumes that the instrument is set
at a primary address of 20 (10100).
2.8.2 Universal Command Sequence
The universal commands are sent by setting ATN low and
then placing the command byte on the bus. For example, the
following gives the LLO command:
ATN'DCL
Note that both ATN and LLO are on the bus simultaneously.
Also, addressing is not necessary.
2.6.3 Device-Dependent Command Sequence
Device-dependent commands are transmitted with ATN
high. However, the device must be addressed to listen first
before the command is transmitted. Table 2-4 shows the se
quence for the following command:
ZIX
This command, which sets the Model 197/1973 to the relative
mode, is described in detail in Section 4.
Note that an UNL command is transmitted before the LAG,
SDC sequence. This is generally done to remove all other
listeners from the bus first so that only the addressed device
responds.
2-6

Table 2-3. Typical Addressed Command Sequence
Step
Command ATN State
Data Bus
ASCII Hex Decimal
1
UNL Set low
? 3F 63
2
LAG* Stays low
4 34 52
3 SDC
Stays low
EOT 04 4
4
Returns high
•Assumes primary address = 20.
Table 2-4. Typical Device-Dependent Command Sequence
Step
Command ATIM State
Data Bus
ASCII
Hex
Decimal
1
UNL
Set low
?
3F
63
2
LAG*
Stays low
4
34 52
3
Data Set high
F
46
70
4
Data
Stays high
0 30
48
5
Data
Stays high
X
58
88
•Assumes primary address = 20.
2-7/2-8

Table 2-1. IEEE-488 Bus Command Summary
State of
Command Type
Command
ATN Line* Comments
Uniline
REN (Remote Enable)
X Set up for remote operation.
EOl (End Or Identify)
X
Sent by setting EOl low.
IPG (Interface Clear)
X Clear Interface.
ATN (Attention) Low Defines data bus contents.
SRQ (Service Request)
X Controlled by external device.
Multiline
Universal
DCL (Device Clear)
Low Returns device to default conditions.
SPE (Serial Poll Enable) Low
Enables serial polling.
SPD (Serial Poll Disable)
Low Disables serial polling.
Addressed SDC (Selective Device Clear)
Low Returns unit to default conditions.
GTL (Go To Local)
Low Returns to local control.
GET (Group Execute Trigger) Low
Triggers device for reading.
Unaddressed
UNL (Unlisten)
Low Removes all listeners from bus.
UNT (Untalk)
Low Removes all talkers from bus.
Device-dependent* *
High Programs Model 197 for various modes.
»X = Don't Care
*See paragraph 4.3 for complete description.
Table 2-2. Hexadecimal and Decimal Command
Codes
Command Hex Value*
Decimal Value
GTL
01
1
SDC
04 4
GET 08
8
DCL
14 20
SPE 18
24
SPD
19
25
LAG
20-3F
32-63
TAG
40-5F
64-95
UNL
3F 63
UNT
5F
95
•Values shown with = 0.
2.6.1 Addressed Command Sequence
Before a device will respond to one of these commands, it
must receive a LAG command derived from its primary ad
dress. Table 2-3 shows a typical sequence for the SDC com
mand. The LAG command assumes that the instrument is set
at a primary address of 20 (10100).
2.6.2 Universal Command Sequence
The universal commands are sent by setting ATN low and
then placing the command byte on the bus. For example, the
following gives the LLO command;
ATN'DCL
Note that both ATN and LLO are on the bus simultaneously.
Also, addressing is not necessary.
2.6.3 Device-Dependent Command Sequence
Device-dependent commands are transmitted with ATN
high. However, the device must be addressed to listen first
before the command is transmitted. Table 2-4 shows the se
quence for the following command:
ZIX
This command, which sets the Model 197/1973 to the relative
mode, is described in detail in Section 4.
Note that an UNL command is transmitted before the LAG,
SDC sequence. This is generally done to remove all other
listeners from the bus first so that only the addressed device
responds.
2-6