Keithley 4853 User manual

KEITH LEY
Model 4853 IEEE-488 Interface
Instruction Manual
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Contains Operating and Servicing Information
Publication Date: October 1987
Document Number: 4853-901-01 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 caU your local Keithley representative, or contact Keithley headquarters in
Cleveland, Ohio. You will 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 OE MERCHANTABILITY OR HTNESS FOR A PARTICULAR USE. THE
REMEDIES PROVIDED HEREIN ARE BUYER'S SOLE AND EXCLUSIVE REMEDIES.
NEITHER KEITHLEY INSTRUMENTS, INC. NOR ANY OE 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 KEITHLEY 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 OE REMOVAL AND INSTALLATION,
LOSSES SUSTAINED AS THE RESULT OE INJURY TO ANY PERSON, OR DAMAGE TO PROPERTY.
KEITHLEY
INSTRUMENTS
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Instruction Manual
Model 4853
IEEE Interface
© 1984 Keithley Instruments, Inc.
Cleveland, Ohio, U.S.A.
Document Number 4853-901-01

SPECIFICATIONS
Maximum Common Mode Volt-Hertz Product: 1 x 10^
Output Data Format:
MANTISSA
4'/: DIGITS
EXPONENT PREFIX
NDCA + 1.2345 E-9
DCA = DC CURRENT
DCL = LOGARITHM
(BASE 10) READING
•N = NORMAL
0 = OVERFLOW
Z = RELATIVE
C = ZERO CHECK
Trigger to First Byte Out:
950ms typical T1 mode.
550ms typical T3 mode.
400ms typical T5 mode.
Address Modes:
Talk Only Mode
Addressable Mode
IEEE-488 BUS IMPLEMENTATION
Muitiiine Commands: DCL, SDC, GET, GTL, UNT, UNL, SPE, SPD.
Uniiine Commands: IFC, REN, EOl, SRQ, ATN.
Interface Functions: SHI, AH1, T5, TEO, L4, LEO, SRI, RL2, PPO, DC1,
DTI, CO, El.
Programmabie Parameters: Zero Check, Range, REL, LOG, EOl, Trigger,
Calibration, SRQ, Status, Output Format, Terminator.
DEVICE-DEPENDENT COMMANDS:
Range:
RO = Auto
R1
R2
R3
2nA
20nA
200nA
R4 = 2fiA
R5 = 20/^A
R6 = 200,»A
R7 = 2mA
Zero Check:
CO = Off
C1 = On
LOG:
DO = LOG Off
D1 = LOG On
Relative:
ZO = REL Off
Z1 = REL On
Trigger:
TO = Continuous on talk
T1 = One-shot on talk
T2 = Continuous on GET
T3 = One-shot on GET
T4 = Continuous on X
T5 = One-shot on X
Execute:
X = Execute other device-dependent commands.
EOl:
KO = EOl Enable
K1 = EOl Disable
Status Word:
UO = Output Status Word
Data Format:
GO = Readings and status word with prefix.
G1 = Readings and status word without prefix.
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
M32 = Clear SRQ Error Mask
M33 = 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.nnnnE ± nn represents 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.

TABLE OF CONTENTS
Para. Title Page
SECTION 1-GENERAL iNFCRMATIGN
1.1 Introduction 1-1
1.2 Model 4853 FEATURES 1-1
1.3 Warranty Information 1-1
1.4 Manual Addenda 1-1
1.5 Safety Symbols and Terms 1-1
1.6 Specifications 1-1
1.7 Unpacking and Inspection 1-1
1.8 Preparation for Use T1
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 Multiline 2-4
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 Sequence 2-5
2.6.1 Addressed Command Sequence 2-5
2.6.2 Universal Command Sequence 2-5
2.6.3 Device-Dependent Command Sequence 2-5
SECTION 3-OPERATION
3.1 Introduction 3-1
3.2 Hardware Considerations 3-1
3.2.1 Typical Controlled Systems 3-1
3.2.2 Bus Connections 3-1
3.2.3 Addressable Mode Selection 3-3
3.2.4 Primary Address Selection 3-3
3.3 Software Assembly 3-4
3.3.1 Controlled Interface Routines 3-4
3.3.2 HP-85 BASIC Statements 3-4
3.3.3 Interface Function Codes 3-5
3.3.4 Model 485 Interface Commands 3-5
3.4 General Bus Command Programming 3-6
3.4.1 REN (Remote Enable) 3-6
3.4.2 IFC (Interface Clear) 3-7
3.4.3 GTL (Go To Local) 3-7
3.4.4 DCL (Device Clear) 3-7
3.4.5 SDC (Selective Device Clear) 3-7
3.4.6 GET (Group Execute Trigger) 3-8
3.4.7 Serial Polling (SPE, SPD) 3-8
3.5 Device-Dependent Command Programming 3-8
3.5.1 Execute (X) 3-9

TABLE OF CONTENTS (CONT.)
Para. Title Page
3.5.2 Zero Check 3-9
3.5.3 LOG(D) 3-9
3.5.4 Range (R) 3-9
3.5.5 Relative (Z) 3-10
3.5.6 Triggering IT) 3-11
3.5.7 EOKK) 3-11
3.5.8 SRQ Mode (M) and Status Byte Format 3-14
3.5.9 Data Format 3-14
3.5.10 Prefix (G) 3-14
3.5.11 Programmable Terminator IY) 3-14
3.5.12 Digital Calibration (V) and Storage (L) 3-14
3.5.13 Status Word (U) 3-15
3.6 Talker Only Operation 3-16
3.6.1 Talk Rate 3-16
SECTIOIM 4-THEORY OF GPERATIOIM
4.1 Introduction 4-1
4.2 Circuit Description 4-1
SECTION 5-MAINTENANCE
5.1 Introduction 5-1
5.2 Installation 5-1
5.3 Special Handling of Static Sensitive Devices 5-1
5.4 Troubleshooting 5-1
SECTION 6-REPLACEABLE PARTS
6.1 Introduction 6-1
6.2 Parts List 6-1
6.3 Ordering Information 6-1
6.4 Factory Service 6-1
6.5 Schematic Diagram and Component Location Drawing 6-1

LIST OF ILLUSTRATIONS
Figure Title Page
2-1 IEEE Bus Configuration 2-2
2-2 Handshake Sequence 2-3
2-3 Command Codes 2-6
3-1 System Types 3-1
3-2 IEEE-488 Connector 3-2
3-3 I EEE-488 Connections 3-2
3-4 Contact Assignments 3-3
3-5 Typical lEEE-488 Bus Driver (one of 16) 3-3
3-6 TO/ADDRESSABLE and Primary Address Switches (Factory Set Address 22 Shown) 3-3
3-7 General Format UO Command 3-12
3-8 Status Byte Format 3-13
3-9 Data Format 3-14
6-1 Model 4853 Installation 6-2
6-2 Model 4853, Component Location Drawing, Dwg. No. 4853-100 6-5
6-3 Model 4853, Schematic Diagram, Dwg. No. 4853-106 6-7
III

LIST OF TABLES
Table Title Page
2-1 IEEE-488 Bus Command Summary 2-1
2-2 Hexadecimal and Decimal Command Codes 2-5
2-3 Typical Addressed Command Sequence 2-5
2-4 Typical Device-Dependent Command Sequence 2-5
3-1 IEEE Contact Designations 3-1
3-2 Primary Address Switch Positions 3-4
3-3 HP-85 IEEE-488 BASIC Statements 3-5
3-4 Model 4853 Interface Fuunctlon Codes 3-6
3-5 IEEE Command Groups 3-6
3-6 General Bus Command 3-6
3-7 Default Conditions (Status Upon Power Up or After SDC or DCL) 3-7
3-8 Device-Dependent Command Summary 3-10
3-9 SRQ Mask Commands 3-12
3-10 Status Byte and Mask Interpretation 3-13
5-1 Static Sensitive Devices 5-1
5-2 Model 4853 Interface Board Checks 5-2
6-1 Model 4853, Parts List 6-1
IV

SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
The Model 4853 IEEE-488 Interface is designed to enhance
the capabilities of the Model 485 Autoranging Picoammeter
by allowing the transmission of data and commands over the
IEEE bus. The Model 4853 provides all the digital logic
necessary to interface the Model 485 to the bus using the
standard IEEE-488-1978 protocol.
1.2 MODEL 4853 FEATURES
Some of the important Model 4853 features include:
•Easy installation. If not already factory installed, the inter
face may be easily installed in the field.
•IEEE-488-1978 Standard. The Model 4853 communicates
with other instruments that use the same IEEE-488-1978
standards.
•Standard IEEE-488 Connector. When the interface is in
stalled in the Model 485, the IEEE-488 connector is available
on the rear panel of the instrument.
•Simple Primary Address Selection. The primary address of
the Model 4853 may easily be set by using the five address
switches on the rear panel of the Model 485.
•Talk Only/Addressable Operation. The interface may be set
for one of two modes of operation. In the talk only mode,
the Model 485 outputs data to other devices (for example,
a printer). In the addressable mode, the Model 485 can both
receive commands and transmit data over the bus through
the interface.
1.3 WARRANTY INFORMATION
Warranty information may be found inside the front cover of
this manual. Should it become necessary to exercise the war
ranty, contact your nearest Keithley representative or the fac
tory to determine the proper course of action. Keithley In
struments, Inc. maintains service facilities in the United
States, United Kingdom, and throughout Europe. Addresses
for these facilities may be found on the warranty page of this
manual. Information concerning the application, operation or
service of your instrument may be directed to the applications
engineer at any of these locations.
1.4 MANUAL ADDENDA
Information concerning improvements or changes to the in
terface which occur after the printing of this manual may be
found on an Addendum sheet included with this manual. Be
sure to review these changes before attempting to use the in
terface.
1.5 SAFETY SYMBOLS AND TERMS
The following safety symbols and terms are used in this
manual and found on the Model 485.
The symbol A on the instrument indicates that the user
should refer to the operating instructions.
Information associated with the WARNING heading explains
dangers that could result in personal injury or death.
Information following the CAUTION heading explains
hazards that could damage the instrument.
1.6 SPECIFICATIONS
Model 4853 specifications may be
preceding this section of the manual.
1.7 INSPECTION
found immediately
The Model 4853 interface was carefully inspected both
mechanically and electrically before shipment. Upon receiv
ing the Model 4853, carefully check all items for any obvious
signs of physical damage that might have occurred during
shipment. Report any damage to the shipping agent im
mediately. Retain the original packing materials in case
reshipment is necessary. The following items are shipped
with every Model 4853 order:
•Model 4853 IEEE-488 interface.
•Hardware necessary for installation.
•Modified Top Cover
•Model 4853 Instruction Manual
•Additional accessories as ordered.
If an additional instruction manual is required, order the
manual package (Keithley Part Number 4853-901-00). The
manual package includes an instruction manual and all perti
nent addenda.
1.8 PREPARATION FOR USE
As shipped, the Model 4853 interface is set to the ad
dressable mode with the primary address set to 22 at the fac
tory. For information on changing these parameters, refer to
Section 3. If the Model 4853 is to be field installed, refer to
Section 5 for necessary installation instructions.
1-1/1-2

SECTION 2
AN OVERVIEW OF THE IEEE-488 BUS
2.1 INTRODUCTION
The IEEE-488 bus is an instrumentation data bus standard
ized by the Institute of Electronic and Electrical Engineers in
1975. The most recent revision of bus standards was made in
1978; hence the complete description for current bus stan
dards is the IEEE-488-1978 designation.
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 a very complex standard. More complete informa
tion on the IEEE-488 bus, which is also frequently referred to
as the GPIB (General Purpose Interface Bus), is available
from the IEEE and a variety of other sources.
2.2 BUS DESCRIPTION
The IEEE bus was designed as a parallel data transfer medium
to optimize data transfer without using an excessive number
of bus lines. In keeping with this goal, the bus has only eight
data lines that are used 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 will have one controller and
one or more instruments to which commands are given and,
in most cases, from which data is received. Generally, there
are three categories that describe device operation. These
designations include: controller; talker; 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.
The Model 485, through the 4853 interface, is capable of be
ing both a talker and a listener, but it does not have controller
capability.
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 or listeners may be present
up to the hardware contraints 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 commanded to listen at once, but
only one device may be a talker at any given time. Otherwise,
communications would be scrambled much like an individual
trying to pick out a single conversation in a large crowd.
Before a device can talk or listen, it must be appropriately ad
dressed. Devices are selected on the basis of their primary ad
dress. To avoid confusion, the addressed device is sent a talk
or listen command derived from its primary address. Normal
ly, each device on the bus has a unique primary address so
that each may be addressed individually. The primary address
of the Model 4853 interface is set to 22 at the factory, but it
may be changed to any value between 0 and 30 as described
in Section 3.
Once the device is addressed to talk or listen, the appropriate
bus transactions will take place. For example, if the Model
4853 is properly addressed to talk, it will normally place its
data string on the bus one byte at a time. The controller will
then read this information, and the appropriate software can
then be used to channel the information to the desired loca
tion. Other bus functions and instrumentation may be con
trolled by special bus commands as described in paragraph
2.3.
2.3 IEEE-488 BUS LINES
The signal lines on the IEEE-488 bus are grouped into three
general categories. The data lines handle bus information,
while the handshake and bus management lines ensure that
proper data transfer and bus operation takes place. Each of
the bus lines are inverted so that low is true. 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 send certain single-line bus commands and ensure an
orderly transfer of data. These lines are used to send the
single-line commands described in paragraph 2.4.
1. ATN (Attention)—The attention line is one of the more im
portant management lines. The state of the ATN line
determines whether information on the data bus is to be
considered data or a command as described in paragraph
2.4.
2. IFC (Interface Clear) —Setting the IFC line true (low)
causes the bus to go to a known state by sending the IFC
command.
3. REN (Remote Enable) —Setting the REN line sends the
REN command. This sets up instruments on the bus for
remote operation.
2-1

4. EOl (End or Identify)—The EOl line is used to terminate a
multi-byte transfer sequence.
5. SRQ (Service Request)—The SRQ line is set low by a bus
device when it requires service from the controller.
TO OTHER DEVICES
DATA BUS
DATA BYTE
TRANSFER
CONTROL
GENERAL
INTERFACE
MANAGEMENT
D101... 8 DATA
(8 LINES)
NRFD ^ handshake
NDAcj
IFC ]
ATN I
SRQ BUS MANAGEMENT
REN i
DEVICE 4
ONLY ABLE
TO TALK
DEVICE 3
ONLY ABLE
TO LISTEN
(PRINTER)
DEVICE 1
ABLE TO
TALK, LISTEN,
AND CONTROL
(COMPUTER)
DEVICE 2
ABLE TO
TALK AND
LISTEN
Figure 2-1. IEEE Bus Configuration
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 will occur 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 accepting
devices. The three bus handshake lines are:
1. DAV (Data Valid)—The source controls the state of the
DAV line.
2. NRFD (Not Ready For Data)—The acceptor controls the
state of the NRFD line.
3. NDAC (Not Data Accepted)—The acceptor also controls
the NDAC line.
The complete handshake sequence for one data byte is
shown in Figure 2-2. Once data 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 NRFD
and NDAC lines have the correct status. Because of the
possibility of a bus hang up, some controllers 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 then goes
high once all 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.
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 then goes
high once all 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.
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 rates, until the NRFD line finally goes high when
the slowest device is ready, and the bus is set to repeat the
sequence with the next byte of data.
The sequence just described is used to transfer both data and
multiline commands. The state of the ATN lines determines
whether the data bus contains data or commands as de
scribed in paragraph 2.4.
2-2

DATA
X
X
SOURCE
DAV
VALID
SOURCE
NRFD-
NDAC
ACCEPTOR
ACCEPTOR
DATA
TRANSFER
BEGIN
DATA
TRANSFER
END
Figure 2-2. Handshake Sequence
2.3.3 Data Lines
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. These eight lines use the convention DI01 through 0108
instead on the usual DO through 07 binary terminology. The
data lines are bidirectional and, as with the remaining bus
signal lines, low is true.
2.4 BUS COMMANDS
While the hardware aspects of the bus are important, the in
terface would be worthless without appropriate commands
to control communications between the various instruments
on the bus. This section will briefly describe the purpose of
the bus commands which are grouped into the following
three general categories:
1. Uniline commands: Sent by setting the associatd bus line
low.
2. Multiline commands: General bus commands which are
sent with the ATN line low.
3. Device-Dependent commands: Special commands that
depend on device configurations; sent with ATN high.
These commands are summarized in Table 2-1. Only com
mands that affect Model 485 operation are covered in this
section.
2.4.1 Uniline Commands
Uniline commands are sent by setting the associated bus line
low. The ATN, IFC and REN commands are sent only by the
system controller. The SRQ command is asserted by an ex
ternal device. The EOl command may be sent by either the
controller or an external device. The following is a brief
description of each command:
1. REN (Remote Enable)—When the controller sends the
REN command, the instrument will be set up for remote
operation before attempting to program over the bus.
2. EOl—The EOl command is transmitted by setting the EOl
(End Or Identify) line low during the last byte of a multi-
byte transfer sequence.
3. IFC (Interface Clear)—The IFC command is sent by setting
the IFC line low; it sets the bus to a known state.
4. ATN (Attention)—The controller sets ATN low when
sending multiline commands. Device-dependent com
mands are sent with ATN high. The ATN line must remain
high while a device transmits its data string.
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.
IFC (Interface Clear)
X
Clears Interface
ATN (Attention)
Low
Defines data bus contents.
SRO (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.
Unaddress UNL (Unlisten)
Low
Removes all listeners from bus.
UNT (Utalk)
Low
Removes all talkers from bus.
Device-dependent**
High
Programs Model 485 for various modes.
•X = Don't Care
**See Section 3 for complete description.
2-3

5. SRQ (Service Request)—The SRQ line is set low by an ex
ternal device when it requires service from the controller. A
serial polling sequence, as described in paragraph 3.4.7,
must be used to determine which device has requested
service.
2.4.2 Universal Commands (Multiline)
Universal commands are multiline commands that require no
addressing. All instrumentation equipped to implement the
command will do so when the command is transmitted over
the bus. As with all multiline commands, the universal com
mands are sent with ATN low.
1. DCL (Device Clear)—After a DCL is sent, instrumentation
equipped to implemented the command will revert to some
known state.
2. SPE (Serial Poll Enable)—The SPE command is the first
step in the serial polling sequence, which is used to deter
mine which instrument has requested service.
3. SPD (Serial Poll Disable)—The SPD command is sent by
the controller to remove all instrumentation on the bus
from the serial poll mode. The Model 485 will no longer
place its status byte on the bus when addressed to talk
after the SPD command is sent.
2.4.3 Addressed Commands
Each of these commands must be preceded by a listen com
mand derived from the device's primary address before the
instrument will respond. Only the addressed device will re
spond to each of these commands:
1. SDC (Selective Device Clear)—The SDC command per
forms essentially the same function as the DCL command
except that only the addressed device will respond.
2. GTL (Go To Local)—The GTL command is used to remove
instruments from the remote mode of operation.
3. GET (Group Execute Trigger)—The GET command is used
to trigger devices to perform some action that depends on
device configuration.
2.4.4 Unaddressed Commands
The two unaddressed commands are used by the controller
to remove all talkers and listeners from the bus simultaneous
ly. No addressing is required to implement these commands.
1. UNL (Unlisten)—All listeners are removed from the bus at
once when the UNL command is placed on the bus.
2. UNT (Untalk)—The controller sends the UNT command to
clear the bus of any talkers.
2.4.5 Device-Dependent Commands
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 complete informa
tion on using these commands with the Model 485, refer to
Section 3. The IEEE-488 bus treats device-dependent com
mands as data in that the ATN line is high when the com
mands are transmitted.
2.5 COMMAND CODES
Each bus command gives a unique code that is transmitted
over the bus as 7 bit ASCII data. This section will briefly ex
plain the code groups which are summarized in Figure 2-3.
Every command is sent with ATN low.
1. Addressed Command Group (ACG)—Addressed com
mands are listed in column 0(B) in the table. Column 0(A)
lists the corresponding ASCII codes.
2. Universal Command Group (UCG) —Columns 1(A) and
1(B) list the Universal commands and the corresponding
ASCII codes.
3. Listen Addressed 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 of the instrument is set to eight, the LAG byte will
correspond to the ASCII "(" character.
4. Talk Address Group (TAG)—TAG primary address values
and the corresponding ASCII characters are listed in col
umns 4(A) through 5(B).
The preceding address groups are all grouped together to
form the Primary Command Group (PCG). The bus also has
another group of commands, called the Secondary Conrr-
mand Group (SCG). These are listed in Figure 2-3 for infor
mational purposes only; the Model 4853 does not respond to
these commands, but other devices may have secondary ad
dressing capability.
NOTE
Commands are normally transmitted with the 7
bit code listed in the table. For most devices, the
condition of D^ (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 D^ is set to 0.
2-4

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 Dy = 0
2.6 COMMAND SEQUENCE
The proper command sequence must be sent by the con
troller before an Instrument will respond as intended. The
universal commands, such as DCL require only that ATM be
set low before the command is sent. Other commands re
quire that the device be addressed to listen first. This section
will briefly describe the bus sequence for several types of
commands.
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 22.
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.
2.6.2 Universal Command Sequence
The universal commands are sent by setting ATN low and
then placing the command on the bus. For example, the
following is placed on the bus to give the DCL command:
ATN'DCL
Note that both the ATN and DCL commands are on the bus
simultaneously. Also, addressing is not necessary.
2.6.3 Device-Dependent Command Sequence
The device-dependent commands are transmitted with ATN
high. However, the device must be addressed to listen first
before the commands are transmitted. Table 2-4 shows the
command sequence for the following:
D1X
This command, which sets the Model 485 to the LOG func
tion, is described in detail in Section 3.
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
6 36
54
3
SDC Stays low
EOT 04 4
4
Returns high
* Assumes primary address = 22.
Table 2-4. Typical Device-Dependent Command Sequence
Step
Command ATN State
Data Bus
ASCII Hex Decimal
1
UNL Set low
?
3F 63
2 LAG*
Stays low 6
36 54
3
Data Set high
F 46 70
4 Data Stays high 0
30 48
5 Data
Stays high
X 58 88
•Assumes primary address = 22.
2-5

N>
I
O)
\D7
Xd6
Bits
\ Xd4
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
1
PRIMARY
ADDRESS
X
1
1
0
X
1
1
1
D3
1
D2
1
Dl
1
Do
I
COLUMN-
ROWl
0 (A)
0 (B)
1 (A)
1 (B)
2 (A)
2 (B)
3 (A) 3 (B) 4 (A)
4 (B)
5 (A)
5 (B) 6(A) 6(8} 7 (A) 7(8)
0
0 0 0 0 NUL
DLE SP
0
0 16
@
0 P
16
P
0
0
0 1 1
SOH GTL
DC1 LLO
1
11 17
A
1
0
17
a
q
0 0 1
0 2 STX
DC2
2
2 18
B
2
R
18 b
r
0
0 11
3 ETX
DC3
#
3
3 19 C
S 19
c 8
0 1
0
0 4
EOT SDC
DC4
DCL
$
44 20
D
4
T
20
d
t
0
1
00 5
ENQ
PPC*
NAK
PPU*
%
5 5
21
E
5 U
21 8 U
0 0
6
ACK
SYN & 66
22 F
6
V
22
f
V
0
7 BEL ETB
7 7
23 G 7
w
23
g w
0 0 0
8 BS
GET CAN SPE
( 8
8 24 H 8
X
24 h
X
0 0
1
9 HT
TCT' EM SPD
)
99
25
1
9 Y 25
y
0 0 10 LF SUB •
10
26
J
10 z 26 z
1
0
11
VT ESC
+
11
27
K
11
1
27
k
{
0
0 12
FF FS 12
<
28 L
12
\
28
1
0
1
13
CR
GS
-
13
-
29
M
13 ]
29
m
i
11 0 14 SO
RS
14
>
30
N
14
A
30 n
-
1 1 1
15 SI
US
/
15
? UNL
0 15
-
UNT
0
DEL
UNIVERSAL
COMMAND
GROUP
(UCGl
COMMAND
GROUP
ACGI
LISTEN
ADDRESS
GROUP
(LAG)
TALK
ADDRESS
GROUP
(TAG)
V
•PPC (Parallel Poll Configure), PPU (Parallel Pull Unconflgure),
LLO (Local Lockout), and TOT (Take Control) not Implemented by Model 4853.
NOTE: Dq = DIOI. ..D7 = DI08
X = Don't Care
PRIMARY
COMMAND
GROUP
(PCG)
y V
y/"
SECONDARY
COMMAND
GROUP
(SDC)
y
Figure 2-3. Command Codes

SECTION 3
OPERATION
3.1 INTRODUCTION
The Model 4853 is designed to interface the Model 485 to
the IEEE-488 bus. The current ranges, and the zero check,
LOG and PEL features are controlled by programming com
mands over the IEEE-488 bus.
This section deals with important hardware and software
aspects of bus operation and describes important program
ming functions in detail. Included are: general bus com
mands, device-dependent commands, status word and
status byte, and other important operating information.
3.2 HARDWARE CONSIDERATIONS
Before the Model 485 can be used with the IEEE-488 bus, the
instrument must be connected to the bus using a suitable
connector. Also, the instrument must be set up for ad
dressable operation and the primary address must be properly
selected as described in this section.
NOTE
Allow the Model 485/4853 to warm up (power
on) for one hour before using.
3.2.1 Typical Controlled Systems
The IEEE-488 bus is a parallel system. As a result, adding
more devices is simply a matter of using more cables to make
the desired connections. Because of this flexibility, system
complexity can range from the very simple to extremely com
plex.
Figure 3-1 shows two typical system configurations. Figure
3-1(a) shows the simplest possible controlled system. The
controller is used to send commands to the instrument,
which sends data back to the controller.
The system becomes more complex in Figure 3-1(b), where
additional instrumentation is added. Depending on program
ming, all data may be routed through the controller, or it may
be transmitted directly from one instrument to another.
For very complex applications, a much larger computer can
be used. Tape drives or disks can then be used to store data.
3.2.2 Bus Connections
The Model 485 is connected to the bus through an IEEE-488
connector which is shown in Figure 3-2. This connector is
designed to be stacked to allow a number of parallel connec
tions on one instrument.
NOTE
To avoid possible mechanical damage, it is
recommended that no more than three connec-
MODEL 485
CONTROLLER
(A) SIMPLE SYSTEM
CONTROLLER
INSTRUMENT
INSTRUMENT
O O
T
MODEL 485
o o o o
9
J
(B) ADDITIONAL INSTRUMENTATION
Figure 3-1. System Types
3-1

tors be stacked on any one instrument. Other
wise, the resulting strain may cause internal
damage.
iS
g
assigments for the various bus lines, while Figure 3-4 shows
contact designations. Contact 18 through 24 are return lines
for the indicated signal lines, and the cable shield is con
nected to contact 12. Each ground line is connected to digital
common in the Model 485.
Table 3-1. IEEE Contact Designations
Figure 3-2. IEEE-488 Connector
A typical connecting scheme for the bus is shown in Figure
3-3. Each cable normally has the standard IEEE connector on
each end. The Keithley Model 7008-3 or 7008-6 cable is ideal
for this purpose. Once the connections are made, the screws
should be tightened securely. The connector is located on the
rear panel of the Model 485.
NOTE
The IEEE-488 bus is limited to a maximum of 15
devices, including the controller. Also, the maxi
mum cable length is 20 meters. Failure to
observe these limits will probably result in erratic
bus operation.
Custom cables may be constructed using the information in
Table 3-1 and Figure 3-4. Table 3-1 lists the contact
Contact IEEE-488
Number Designation
Type
1
DI01 Data
2
DI02
Data
3 DI03 Data
4 DI04
Data
5 EOl (24)* Management
6
DAV
Handshake
7 NRFD
Handshake
8 NDAC
Handshake
9 IFC Management
10 SRQ Management
11 ATN
Management
12 SHIELD
Ground
13
DI05
Data
14 DI06
Data
15 DI07 Data
16 □108 Data
17 REN (24)*
Management
18
Gnd, (6)*
Ground
19
Gnd, (7)*
Ground
20
Gnd, (8)*
Ground
21
Gnd, (9)*
Ground
22 Gnd, (10)* Ground
23 Gnd, (ID* Ground
24 Gnd, LOGIC Ground
•Numbers in parentheses refer to signal ground
return of reference contact number. EOl and
REN signal lines return on contact 24.
INSTRUMENT INSTRUMENT
INSTRUMENT
CONTROLLER
Figure 3-3. IEEE-488 Connections
3-2

CONTACT 13
CONTACT 24
and then powered-up again before it will recognize the new
switch position.
CONTACT 1 CONTACT 12
Figure 3-4. Contact Assignments
CAUTION
The voltage between IEEE common and
ground must not exceed 30V or damage to
the instrument may occur.
A typical signal line bus driver is shown in Figure 3-5. With
the configuration shown, the driver has bidirectional capabili
ty. When the I/O control line is high, the line is configured as
an output line. When the control line is low, the driver is set
up for input operation. Note that not all signal lines have
bidirectional capability. Some lines, such as ATN, will always
be configured as an output line in the controller and as an in
put line for all other devices on the bus.
DATA^
LINE
I/O
CONTROL
O OUTPUT
Figure 3-5. Typical IEEE-488 Bus Driver (one of 16)
3.2.3 Addressable Mode Selection
The Model 4853 must be set to the addressable mode when
used with an external controller. Mode selection is done with
the TO/ADDRESSABLE mode selection switch located on
the rear panel of the Model 485. This switch is grouped with
those that set the primary address; these switches are located
on the rear panel of the Model 485. Figure 3-6 shows the
ADDRESSABLE position for the switch.
The TO/ADDRESSABLE switch is read only upon power-up.
If the mode is changed, the Model 485 must be turned off
TALKER ONLY
(TO) MODE
MSB
ADDRESSABLE
MODE
Figure 3-6. TO/ADDRESSABLE and Primary Address
Switches (Factory Set Address 22 Shown)
3.2.4 Primary Address Selection
The Model 485 must receive a listen command before it will
respond to the addressed or device-dependent commands
sent over the bus. Similarly, a talk command must be sent to
the Model 485 before it will transmit its data string, status
word, or status byte. Those talk and listen commands are
derived from the primary address of the instrumet. The
primary address of the Model 4853 is set to 22 at the factory,
but it may be set to any value between 0 and 30 by placing
the primary address switches which are shown in Figure 3-6,
in the desired position. The primary address specified in the
controller's programming language must agree with the
primary address of the Model 4853.
NOTE
The primary address switch positions are read
only upon power-up. If the address is changed
the Model 485 must be turned off and then
powered-up again before the new address can
be used.
Figure 3-6 shows the correct positions for the factory set
value of 22, if a different address is required, the primary ad
dress may be changed as outlined in Table 3-2.
NOTE
If other instrumentation is also connected to the
bus, be sure that each device has a different
primary address. If this precaution is not ob
served, erratic bus operation may result.
The primary address switches are binary weighted; A1 is the
least significant bit, while A5 the most significant bit. For ex
ample, the binary value for the factory set primary address of
eight is 01000. Use the tip of a pen or pencil to operate the
switches.
NOTE
No instrument on the bus (including the Model
485) should be operated with a primary address
3-3

r
of 31, even though it Is possible to set the
switches to those positions (11111). This ad
dress is reserved for the UNL and UNT com
mands; instrument will respond by removing
themselves from the talk or listen modes if
primary address 31 is used.
Table 3-2. Primary Address Switch Positions
Primary
Address
5 4 3 2 1
00
0 0 00
1 0 0 0 0 1
2
0 0 0 1 0
3
0 0 0 1 1
4 0 0 1 0 0
5 0 0 1 0 1
6 0 0 1 1 0
7 0 0 1 1 1
8
0 1 0 0 0
9 0 1 0 0 1
10
0 1 0 1 0
11 0 1 0 1 1
12
0 1 1 0 0
13
0 1 1 0 1
14 0 1 1 1 0
15
0 1 1 1 1
16
1 0 0 0 0
17 1 0 0 0 1
18
1 0 0 1 0
19
1 0 0 1 1
20
1 0 1 0 0
21
1 0 1 0 1
22
1 0 1 1 0
23
1 0 1 1 1
24 1 1 0 0 0
25
1 1 0 0 1
26
1 1 0 1 0
27
1 1 0 1 1
28
1 1 1 0 0
29
1 1 1 0 1
30
1 1 1 1 0
3.3 SOFTWARE ASSEMBLY
The most sophisticated computer in the world would be
useless without the necessary software. This basic require
ment is also true of the IEEE-488 bus, which requires the use
of handler routines as described in this section.
3.3.1 Controller Interface Routines
Before a controller can be used with the IEEE-488 interface,
the user must make certain that appropriate handler software
is present within the controller. With the HP-85 computer, for
example, the HP-85 interface card must be used with an addi
tional I/O ROM, which contains the necessary handler soft
ware.
Other small computers that can be used as controllers have
limited IEEE command capability. The PET/CBM computers,
for example, are incapable of sending the universal and ad
dressed multiline commands from BASIC, although most of
these commands may be sent through machine-language
routines. The capabilities of other small computers depends
on the particular interface being used. Often, little software
"tricks" are required to achieve the desired results.
From the preceding discussion, the message is clear: make
sure the proper software is being used with the interface.
Often, the user may incorrectly suspect that a hardware prob
lem is causing an intermittent fault, when it was the software
that was causing the problem all along.
3.3.2 HP-85 BASIC Statements
Many of the programming instructions use examples written
in Hewlett-Packard Model 85 BASIC. The HP-85 was chosen
for these examples because it has a large number of BASIC
statements that control IEEE-488 operation. This section
covers those HP-85 BASIC statements that are essential to
Model 4853 operation.
A complete list of HP-85 IEEE-488 BASIC statements is
shown in Table 3-3. All the statements in the table have a one
or three digit interface select code, which is set to 7 at the
factory. The last two digits of those statements that require a
three digit argument specify the primary address. Generally,
only those commands that actually require an address to be
sent over the bus need the primary address to be specified.
The statements in the table with the three digit arguments
assume that the primary address of the device (in this case
the Model 4853) is set at 22. Other primary addresses require
that the last two digits be set to the corresponding value. Fdr
example, to send a GTL command to device 21, the following
BASIC statement would be used: LOCAL 721.
Some of the statements in the table have two forms; the ex
act configuration used depends on the desired command. For
example, CLEAR 7 will cause a DCL to be sent, while CLEAR
722 causes an SDC to be transmitted to device 22.
The third column of Table 3-3 lists the mnemonics for the
command sequences. While most of these have been
covered before, a couple of points should be noted. As
described earlier, the ATN line is set low by the controller if
the data bus contains a multiline command. This is indicated
in the table by AN Ding the ATN mnemonics with the first
command on the bus. For example, ATN.GET means that
ATN and GET are sent simultaneously.
Two commands not previously covered are MLA (My Listen
Address) and MTA (My Talk Address). These are ordinary
PCG (Primary Command Group) addresses sent by the HP-85
to facilitate bus operation in some situations. The Model 4853
will normally ignore these commands, but other device may
3-4

require that MLA and MTA be present in the command se
quence under certain circumstances.
NOTE
The HP-85 address is set to 21 at the factory.
Since each device on the bus must have
a unique primary address, do not set the Model
485 to the address to avoid conflicts with the
HP-85.
3.3.3 Interface Function Codes
The interface function codes are part of the IEEE-488-1978
standards. These codes define an instrument's ability to sup
port various interface functions and should not be confused
with programming commands found elsewhere in this
manual.
Table 3-4 lists the codes for the Model 4853. These codes are
also listed for convenience on the rear panel of the instrument
immediately above the IEEE connector. The numeric value
following each one or two letter code defines Model 485
capabilities as follows:
1. SHI (Source Handshake Function)—The ability for the
Model 485 to initiate the transfer of message/data on the
data bus is provided by the SHI function.
2. AH1 (Acceptor Handshake Function)—The ability for the
Model 485 to guarantee proper reception of
message/data on the data bus is provided by the AH
function.
3. T5 (Talker Function)—The ability for the Model 485 to
send device-dependent data over the bus (to other
devices) is provided by the T function. Model 485 talker
capabilities exist only after the instrument has been ad
dressed to talk.
4. L4 (Listener Function)—The ability for the Model 485 to
receive device-dependent data over the bus (from other
devices) is provided by the L function. Listener function
capabilities of the Model 485 exist only after it has been
addressed to listen.
5. SRI (Service Request Function)—The ability for the
Model 485 to request service from the controller is pro
vided by the SR function.
6. RL2 (Remote-Local Function)—The ability for the Model
485 to be placed in the remote or local modes in provided
by the RL function.
7. PRO (Parallel Poll Function)—The Model 485 does not
have parallel polling capabilities.
8. DC1 (Device Clear Function)—The ability for the Model
485 to be cleared (initialized) is provided by the DC func
tion.
9. DTI (Device Trigger Function)—The ability for the Model
485 to have its readings triggered is provided by the DT
function.
10. CO (Controller Function)—The Model 485 does not have
controller capabilities.
11. TEO (Extended Talker Capabilities)—The Model 485 does
not have extended talker capabilities.
12. LEO (Extended Listener Capabilities)—The Model 485
does not have extended listener capabilites.
3.3.4 Model 485 Interface Commands
Interface commands controlling Model 485 operation are
listed in Table 3-5. Not included in the table are device-
dependent commands, which are covered in detail in
paragraph 3.5.
Table 3-3. HP-85 IEEE-488 BASIC Statements
Statement Action
Bus Command Sequence
ABORTIO 7 Send IFC.
IFC
CLEAR 7
Send DCL.
ATN'DCL
CLEAR 722
Send SDC to device 22.
ATN*UNL;MTA;LAG;SDC
ENTER 722;A$
Device 22 addressed to talk.
ATN*UNL;MLA;TAG;ATN;data
Data placed in A$.
LOCAL 722
Send GTL to device 22.
ATN*UNL;MTA;LAG;GTL
OUTPUT 722;A$
Device 22 addressed to listen.
ATN* MTA; U N L; LAG; ATN; data
Transmit A$.
REMOTE 7
Set REN true.
REN
REMOTE 722
Send REN true. Address device
REN;ATN*UNL;MTA;LAG
22 to listen.
RESET 7
Send IFC, cancel REN.
IFC;REN;^
SPOLL(722)
Address device 22 to talk.
ATN*UNL;MLA;TAG;SPE;ATN;
Conduct serial poll.
status byte;ATN*SPD;UNT
TRIGGER 7
Send GET
ATN'GET
TRIGGER 722
Address device 22 to listen.
ATN»UNL;MTA;LAG;GET
Send GET.
3-5