National Instruments Switch GPIB COM User Manual

GPIB-COM  
User Manual  
June 1990 Edition  
Part Number 320197-01  
© Copyright 1989, 1991 National Instruments Corporation.  
All Rights Reserved.  
 
Limited Warranty  
The GPIB-COM is warranted against defects in materials and workmanship for a period of two  
years from date of shipment. National Instruments will repair or replace equipment which proves  
to be defective during the warranty period. This warranty includes parts and labor. A Return  
Material Authorization (RMA) number must be obtained from National Instruments before any  
equipment is returned for repair. Faults caused by misuse are not covered under the warranty.  
During the warranty period, the owner may return failed parts to National Instruments for repair.  
National Instruments will pay the shipping costs of returning the part to the owner. All items  
returned to National Instruments for repair must be clearly marked on the outside of the package  
with an RMA number.  
No other warranty is expressed or implied. National Instruments shall not be liable for  
consequential damages. Contact National Instruments for more information.  
Important Notice  
The material in this manual is subject to change without notice. National Instruments assumes no  
responsibility for errors which may appear in this manual. National Instruments makes no  
commitment to update, nor to keep current, the information contained in this document.  
Copyright  
Under the copyright laws, this manual may not be copied, photocopied, reproduced, translated, in  
whole or in part, without the prior written consent of National Instruments Corporation.  
Trademark  
IBM is a registered trademark of International Business Machines Corporation.  
 
FCC/DOC Radio Frequency Interference Compliance  
This equipment generates and uses radio frequency energy and, if not installed and used in strict  
accordance with the instructions in this manual, may cause interference to radio and television  
reception. This equipment has been tested and found to comply with (1) the limits for a Class B  
computing device, in accordance with the specifications in Part 15 of U.S. Federal  
Communications Commission (FCC) Rules, and (2) the limits for radio noise emissions from  
digital apparatus set out in the Radio Interference Regulations of the Canadian Department of  
Communications (DOC). These regulations are designed to provide reasonable protection  
against interference from the equipment to radio and television reception in residential areas.  
There is no guarantee that interference will not occur in a particular installation. However, the  
chances of interference are much less if the equipment is used according to this instruction  
manual.  
If the equipment does cause interference to radio or television reception, which can be  
determined by turning the equipment on and off, one or more of the following suggestions may  
reduce or eliminate the problem.  
Operate the equipment and the receiver on different branches of your AC electrical system.  
Move the equipment away from the receiver with which it is interfering.  
Relocate the equipment with respect to the receiver.  
Reorient the receiver's antenna.  
Be sure that the equipment is plugged into a grounded outlet and that the grounding has not  
been defeated with a cheater plug.  
If necessary, consult National Instruments or an experienced radio/television technician for  
additional suggestions. The following booklet prepared by the FCC may also be helpful: How to  
Identify and Resolve Radio-TV Interference Problems. This booklet is available from the U.S.  
Government Printing Office, Washington, DC 20402, Stock Number 004-000-00345-4.  
 
Preface  
Introduction to the GPIB-COM  
The GPIB-COM is a high-performance talk/listen interface board that makes communication  
possible between IEEE-488 devices and IBM personal computers and compatibles (hereafter  
referred to as PCs) equipped with software that uses the serial ports.  
Organization of This Manual  
This manual is divided into the following sections:  
Section One, Introduction, contains a brief description of the GPIB-COM including a listing of its  
features, accessories, and components.  
Section Two, Configuration and Installation, describes how to configure and install the GPIB-  
COM into your system.  
Section Three, Function Description, shows a block diagram of the GPIB-COM and describes the  
functional components of the GPIB-COM.  
Section Four, Running Diagnostic Tests, describes how to run the diagnostic tests that are shipped  
with the GPIB-COM.  
Section Five, Programming the GPIB-COM, presents a description of the GPIB-COM Serial Port  
Emulator registers and information on programming the IBM serial adapter.  
Appendix A, Specifications, lists the specifications of the GPIB-COM board.  
Appendix B, Multiline Interface Command Messages, contains an ASCII chart and a list of the  
corresponding GPIB messages.  
Appendix C, Operation of the GPIB, describes GPIB terminology and protocol for users  
unfamiliar with the GPIB.  
Related Documents  
The following documents contain information that may be helpful as you read this manual:  
ANSI/IEEE Std 488-1978, IEEE Standard Digital Interface for Programmable  
Instrumentation  
IBM Options and Adapters Manual  
IBM PC Technical Reference Manual  
IBM Disk Operating System Manual  
INS8250A Data Sheet, National Semiconductor  
© National Instruments Corporation  
v
GPIB-COM User Manual  
 
Preface  
Abbreviations Used in This Manual  
The following abbreviations are used in the text of this manual.  
is less than or equal to  
is greater than or equal to  
plus or minus  
ampere  
±
A
C
hex  
in.  
Celsius  
hexadecimal  
inch  
I/O  
kbyte  
m
Mbyte  
MHz  
msec  
r
input/output  
1000 bytes  
meter  
megabyte  
megahertz  
millisecond  
read  
r/w  
sec  
V
VDC  
w
read/write  
second  
volt  
volts direct current  
write  
GPIB-COM User Manual  
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© National Instruments Corporation  
 
Contents  
Section One  
GPIB-COM Characteristics............................................................................................1-1  
Section Two  
Configuration..................................................................................................................2-1  
Switch and Jumper Settings................................................................................2-3  
Section Three  
The GPIB-COM Interface ..............................................................................................3-1  
GPIB-COM Components...............................................................................................3-3  
Address Decoding ..............................................................................................3-3  
Configuration Jumpers .......................................................................................3-3  
GPIB Acceptor and Source Handshaking...........................................................3-3  
Mode Control Logic............................................................................................3-3  
Interrupt Control Logic .......................................................................................3-3  
Direction Buffers ................................................................................................3-4  
Section Four  
The GPIB-COM Test Commands..................................................................................4-1  
-1 printer test.......................................................................................................4-1  
-c change COM configuration.............................................................................4-3  
Section Five  
The GPIB-COM Registers .............................................................................................5-1  
© National Instruments Corporation  
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GPIB-COM User Manual  
 
Contents  
Programming the Serial Adapter ....................................................................................5-16  
Interrupt-Driven Method.....................................................................................5-16  
Appendix A  
Specifications.......................................................................................................................A-1  
Appendix B  
Multiline Interface Command Messages..................................................................B-1  
Appendix C  
Operation of the GPIB......................................................................................................C-1  
Types of Messages .........................................................................................................C-1  
Talkers, Listeners, and Controllers..................................................................................C-1  
GPIB Signals..................................................................................................................C-2  
Data Lines.......................................................................................................................C-3  
NDAC (not data accepted)..................................................................................C-3  
DAV (data valid) ................................................................................................C-4  
Interface Management Lines...........................................................................................C-4  
ATN (attention)...................................................................................................C-4  
REN (remote enable)..........................................................................................C-4  
SRQ (service request).........................................................................................C-4  
EOI (end or identify) ..........................................................................................C-4  
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© National Instruments Corporation  
 
Contents  
Figure 1-1. GPIB-COM Board ................................................................................................1-2  
Figure 2-3. Jumper W1 Settings ..............................................................................................2-4  
Tables  
Table 2-1. IBM PC Serial Port Adapters ................................................................................2-3  
Table 2-2. Factory Default Settings and Optional Configurations...........................................2-3  
© National Instruments Corporation  
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GPIB-COM User Manual  
 
Section One  
Introduction  
This section contains a brief description of the GPIB-COM interface and a list of its characteristics  
and components.  
GPIB-COM Characteristics  
The National Instruments GPIB-COM is a high-performance talk/listen interface that converts data  
between a standard serial port format and IEEE-488 General Purpose Interface Bus (GPIB)  
format for use with IEEE-488 printers and plotters. It can be used with any serial port software  
on the PC. The GPIB-COM looks like a standard serial port to the IBM PC operating system and  
software. It can be used to interface IEEE-488 devices to any PC software that uses the serial  
ports.  
The GPIB-COM has the following hardware features:  
emulates the standard PC serial adapter interface so that no additional software is needed  
can be configured as either COM1, COM2, COM3, or COM4  
compatible with any software using the serial ports on the IBM PC and its compatibles  
transparent addressing of unaddressed Talkers and Listeners  
choice of talk-only mode for use with listen-only printers and plotters  
choice of REN mode, which operates an instrument in the remote mode  
choice of SRQ enable, which allows monitoring of asynchronous service requests  
choice of IFC mode, which sends an interface clear when the computer is powered on  
© National Instruments Corporation  
1-1  
GPIB-COM User Manual  
 
 
Introduction  
Section One  
Figure 1-1 shows the GPIB-COM interface board.  
Figure 1-1. GPIB-COM Board  
What Your Kit Should Contain  
Your kit should contain the following components:  
Item  
Part Number  
GPIB-COM interface board  
GPIB-COM User Manual  
180750-01  
320197-01  
420212-45  
GPIB-COM Diagnostic Test Diskette  
Note: The GPIB-COM Diagnostic Test Diskette contains the com.exediagnostic test  
that is described in Section Four, Running Diagnostic Tests.  
Make sure each of these items is in your kit. If any item is missing, contact National Instruments.  
GPIB-COM User Manual  
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© National Instruments Corporation  
 
   
Section One  
Introduction  
Optional Equipment  
Item  
Part Number  
Double-Shielded Cables:  
GPIB Type X2 Cable - 1 m  
GPIB Type X2 Cable - 2 m  
GPIB Type X2 Cable - 4 m  
763061-01  
763061-02  
763061-03  
* In order to meet FCC emission limits for a Class B device, you must use a shielded  
GPIB cable. Operating this equipment with a non-shielded cable may cause interference  
to radio and television reception in residential areas.  
© National Instruments Corporation  
1-3  
GPIB-COM User Manual  
 
 
Section Two  
Configuration and Installation  
This section contains information on how to configure and install the GPIB-COM into your  
system.  
Configuration  
Figure 2-1 shows the locations of the GPIB-COM configuration jumpers and switches.  
Figure 2-1. GPIB-COM Parts Locator Diagram  
© National Instruments Corporation  
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GPIB-COM User Manual  
 
   
Configuration and Installation  
Section Two  
When installing the GPIB-COM you must determine which serial port the GPIB-COM board will  
respond to and select the appropriate base address and interrupt level. The GPIB-COM can be  
configured to one of four base addresses:  
3F8 for Serial Port 1  
2F8 for Serial Port 2  
3E8 for Serial Port 3  
2E8 for Serial Port 4  
Note: DOS and BIOS only recognize base addresses 3F8 and 2F8.  
The GPIB-COM is shipped from the factory set to 3F8. It must be reconfigured to another base  
address if another device (such as a printer adapter card or a built-in serial port) is already at that  
address.  
DOS has reserved device names for the serial ports it finds in the system: COM1 and COM2.  
The serial port adapters are named in the order in which they are found. When the computer is  
powered on, DOS searches the serial port addresses for installed adapters. It first searches 3F8,  
then 2F8. If only one device is installed, that device is named COM1 regardless of what its I/O  
address is. If there is more than one serial device installed, the first one found is assigned COM1  
and the second one found is assigned COM2.  
Some communications software also recognizes COM3 (base address 3E8) and COM4 (base  
address 2E8). If you wish to use COM3 or COM4, set the jumpers to the desired base address as  
shown in Figure 2-2. DOS and BIOS do not recognize COM3 or COM4. Consult your software  
documentation to see which interrupt level, if any, is required. If interrupts are not used, the  
jumper can be removed or stored with only one side on a pin.  
The GPIB-COM may need to be reconfigured if its interrupt level conflicts with another device. If  
the base I/O address of the GPIB-COM does not conflict with any other device in your computer  
and the GPIB-COM still does not work with your software package, reconfigure the GPIB-COM  
to a different interrupt level.  
GPIB-COM User Manual  
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© National Instruments Corporation  
 
Section Two  
Configuration and Installation  
Table 2-1 shows the standard base I/O address and interrupt level for each serial port.  
Table 2-1. IBM PC Serial Port Adapters  
Name of Port  
Serial Port 1  
Serial Port 2  
Serial Port 3  
Serial Port 4  
Base I/O Address (hex)  
Interrupt Level  
3F8  
2F8  
3E8  
2E8  
4
3
Not Used  
Not Used  
Switch and Jumper Settings  
Table 2-2 shows the factory settings and optional configurations for the switches and jumpers on  
the GPIB-COM.  
Table 2-2. Factory Default Settings and Optional Configurations  
GPIB-COM  
Base I/O Address  
Interrupt Level  
Default  
3F8  
Optional  
2F8, 3E8, 2E8  
3
4
If you need to change the factory settings, continue on. If you do not need to change the factory  
settings, skip to Installation later in this section.  
Base I/O Address and Interrupt Selection  
The base I/O address and interrupt line used by the GPIB-COM are determined by the jumpers  
located at positions W2 and W5. The jumpers are set at the factory for base I/O address 3F8 hex  
and interrupt level 4.  
© National Instruments Corporation  
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GPIB-COM User Manual  
 
   
Configuration and Installation  
Section Two  
Figure 2-2 shows the four possible combinations of jumper settings.  
W5  
W5  
XF8  
XE8  
2X8  
XF8  
XE8  
2X8  
3X8  
3X8  
IRQ3  
IRQ3  
IRQ4  
IRQ4  
a. COM1: Jumpers Set to Base I/O Address  
3F8 hex and Interrupt Level 4 (Default)  
b. COM2: Jumpers Set to Base I/O Address  
2F8 hex and Interrupt Level 3  
W5  
W5  
XF8  
3X8  
XE8  
2X8  
XF8  
3X8  
XE8  
2X8  
IRQ3  
IRQ3  
IRQ4  
IRQ4  
c. COM3: Jumpers Set to Base I/O Address  
3E8 hex (Interrupts Not Used)  
d. COM4: Jumpers Set to Base I/O Address  
2E8 hex (Interrupts Not Used)  
Figure 2-2. Possible Settings for GPIB-COM Jumpers  
Talk/Listen Modes  
If you are using your GPIB-COM with a listen-only printer or plotter, you can configure the  
GPIB-COM for a talk-only mode. In this mode, the GPIB-COM is always a Talker and never  
sends any interface commands. To set the talk-only mode, change jumper W1 from T/L to T as  
shown in Figure 2-3:  
W1  
W1  
a. Talk/Listen  
(Default)  
b. Talk Only  
Figure 2-3. Jumper W1 Settings  
GPIB-COM User Manual  
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© National Instruments Corporation  
 
   
Section Two  
Configuration and Installation  
Talk/Listen Address and Special Function Selection  
The GPIB-COM interface board has eight onboard DIP switches you can use to configure the  
GPIB controller responsibilities. In the talk/listen mode, the first five switches set the talk or listen  
address of the external device(s) that will be attached to the GPIB-COM. In the talk-only mode,  
the GPIB-COM does not send a talk or listen address.  
The three remaining switches (REN, IFC, and SRQ) have the following special functions:  
Note: An asterisk (*) after a signal name indicates that the signal is inverted (negative logic).  
REN*  
Asserts/unasserts the Remote Enable (REN) line that places an instrument in remote  
mode. The ON position enables REN. The OFF position disables REN.  
IFC*  
Enables/disables the Interface Clear (IFC) option on the GPIB-COM. If enabled, the  
GPIB-COM issues an IFC when it is initialized. The ON position enables IFC on  
initialization. The OFF position holds IFC unasserted.  
SRQ*  
Enables/disables the Service Request (SRQ) option. If enabled, the GPIB-COM  
monitors the SRQ line through the Parity Error Bit (PE) in the Line Status Register.  
When the switch is ON, the PE bit reflects the status of the SRQ line. When the  
switch is OFF, the PE bit is always clear.  
The GPIB-COM factory default switch configuration is for device listen address 5, REN* not  
asserted, IFC* enabled, and SRQ* enabled. Figure 2-4 shows the factory default switch settings  
for the GPIB-COM.  
Key  
= side you must press down for default setting; Off = 1; On =  
This side down for logic 1  
This side down for logic 0  
U13  
1
2
4
8
16  
REN  
IFC  
SRQ  
Figure 2-4. Switch Setting for REN* OFF, IFC* ON, SRQ* ON, and Listen Address 5  
(Default Setting)  
© National Instruments Corporation  
2-5  
GPIB-COM User Manual  
 
 
Configuration and Installation  
Section Two  
Figure 2-5 shows the switch configuration needed when using a device with listen address 10 hex.  
The listen address varies with each device so check the listen address of your device and set these  
five bits accordingly.  
Key  
= side you must press down for Listen Address 10;  
Off = 1; On = 0  
= used for setting REN* ON, IFC* ON, and SRQ* ON  
This side down for logic 1  
This side down for logic 0  
1
U13  
2
4
8
16  
REN  
IFC  
SRQ  
Figure 2-5. Listen Address Setting for Listen Address 10 Hex  
GPIB-COM User Manual  
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© National Instruments Corporation  
 
 
Section Two  
Configuration and Installation  
Figure 2-6 shows the switch configuration for REN* asserted, IFC* disabled, and SRQ* disabled.  
Key  
= side you must press down for REN* ON, IFC* OFF, and  
SRQ* OFF; Off = 1; On = 0.  
= used for setting Listen Address  
This side down for logic 1  
This side down for logic 0  
U13  
1
2
4
8
16  
REN  
IFC  
SRQ  
Figure 2-6. Switch Setting for REN* ON, IFC* OFF, and SRQ* OFF  
Installation  
Once you have changed, verified, and recorded the switches and jumper settings, you are ready to  
install the GPIB-COM.  
The following steps are general installation instructions. Consult the user manual or technical  
reference manual of your personal computer for specific instructions and warnings.  
1. Turn off your computer.  
2. Remove the plug from its power source.  
3. Remove the top cover or access port to the I/O channel.  
4. Remove the expansion slot cover on the back panel of your computer.  
5. Insert the GPIB-COM in an unused full-length slot with the IEEE-488 receptacle sticking out  
of the opening of the back panel. It may be a tight fit, but do not force the board into place.  
6. Screw the right angle mounting bracket of the GPIB-COM to the back panel rail of your  
computer.  
© National Instruments Corporation  
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GPIB-COM User Manual  
 
 
Configuration and Installation  
Section Two  
7. Check the installation.  
8. Replace the expansion slot cover of your computer.  
9. Connect the GPIB cable to the GPIB-COM.  
Special Considerations When Using the GPIB-COM  
The GPIB-COM does not support XON/XOFF protocols. If your application software uses  
XON/XOFF protocols, send your printer and plotter output to a file on disk. From DOS, send  
your file to the GPIB-COM by using the DOS command:  
copy filename COM1:  
copy filename COM2:  
The DOS MODE command is used to set the RS-232 parameters that will be used when COM1  
and COM2 are accessed through DOS. Sometimes a timeout error may occur when writing  
through the GPIB-COM to a slow device such as a printer or a plotter. If this happens, use the  
MODE command to disable the timeout function by typing MODE COM1:12,,,,P. Some  
software applications use the COM port baud rate setting to control the data transmission speed.  
To obtain the fastest possible transfer rates, set the baud rate setting to 9600 baud. The Pat the end  
disables the timeout. For more information on the MODE command, refer to the IBM Disk  
Operating System Manual. This command can also be used in an autoexec.batfile to disable  
timeouts when you start up the computer.  
GPIB-COM User Manual  
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© National Instruments Corporation  
 
 
Section Three  
Function Description  
This section contains a block diagram of the GPIB-COM, followed by a description of each of its  
functional components.  
The GPIB-COM Interface  
The GPIB-COM is a completely transparent interface between GPIB devices and any IBM PC  
software that uses serial ports. A set of I/O registers identical to those on the standard IBM serial  
adapter is used. On the GPIB side, the GPIB-COM includes a limited subset of interface  
functions that address a GPIB device to listen when the computer sends data to the serial port and  
to talk when the computer is waiting to receive data from the serial port. In order to be able to  
respond immediately to commands and data sent to the serial port, the GPIB-COM must be the  
GPIB System Controller and cannot work with other Controllers present.  
© National Instruments Corporation  
3-1  
GPIB-COM User Manual  
 
 
Function Description  
Section Three  
Figure 3-1 shows a block diagram of the GPIB-COM.  
IRQ3  
Config.  
Jumpers  
Interrupt  
Control  
IRQ4  
Config.  
Jumpers  
Address Bus  
AEN  
INS8250A  
Compatible  
Registers  
Address  
Decoding  
IOW*  
IOR*  
Direction  
Buffer  
Data Bus  
Mode Control  
Logic  
Direction  
Buffer  
Acceptor  
Handshake  
Source  
Handshake  
GPIB  
Transceivers  
GPIB  
Figure 3-1. Block Diagram of GPIB-COM  
GPIB-COM User Manual  
3-2  
© National Instruments Corporation  
 
 
Section Three  
Function Description  
GPIB-COM Components  
The interface consists of the following functional components:  
Address Decoding  
Configuration Jumpers  
INS8250A Compatible Registers  
GPIB Acceptor and Source Handshaking  
Mode Control Logic  
Interrupt Control Logic  
Direction Buffers  
GPIB Transceivers  
Address Decoding  
Address decoding monitors the PC address bus to recognize when a GPIB-COM address is  
present and enables a read and/or write to its registers.  
Configuration Jumpers  
These onboard jumpers select the base address, GPIB controller mode, and interrupt request line  
used by the GPIB-COM.  
INS8250A Compatible Registers  
The main component of an IBM PC compatible serial adapter is an INS8250A Asynchronous  
Communications chip or its equivalent, which handles RS-232 communication. The INS8250A  
compatible registers on the GPIB-COM emulate the serial adapter registers so that the GPIB-  
COM will operate transparently with any serial port driver.  
GPIB Acceptor and Source Handshaking  
This circuitry converts PC serial port handshaking into GPIB handshaking. This process is  
completely software-transparent.  
Mode Control Logic  
This circuitry determines whether the GPIB-COM should be a Talker (and the target device a  
Listener) or a Listener (and the target device a Talker).  
Interrupt Control Logic  
This circuitry generates and masks interrupts on GPIB conditions which correspond to the  
conditions that would cause the INS8250A circuit to generate an interrupt.  
© National Instruments Corporation  
3-3  
GPIB-COM User Manual  
 
 
Function Description  
Section Three  
Direction Buffers  
These buffers control the direction in which data information travels.  
GPIB Transceivers  
The GPIB-COM is interfaced to the IEEE-488 bus by National Semiconductor 75160A and  
75162A transceivers. These integrated circuits are specifically designed to provide power-  
up/power-down bus protection (glitch-free). The GPIB-COM counts as one IEEE-488 bus load,  
thereby allowing an additional 14 devices to be connected before exceeding the bus loading  
restrictions imposed by the IEEE-488.  
GPIB-COM User Manual  
3-4  
© National Instruments Corporation  
 
 
Section Four  
Running Diagnostic Tests  
The GPIB-COM Test Commands  
The GPIB-COM Diagnostic Tests can be used to verify the configuration of the GPIB-COM and  
its connection to a GPIB printer or plotter.  
To run a GPIB-COM diagnostic test, connect a printer or plotter to the GPIB and run the program  
com.exefrom the GPIB-COM diagnostic test diskette. The following message will appear on the  
screen:  
NATIONAL INSTRUMENTS GPIB-COM DIAGNOSTIC TESTS  
This program assumes the GPIB-COM is configured at base address  
3F8 (COM1).  
If you reconfigured your GPIB-COM you must change the address  
that this program uses. To do this, enter command c from the  
menu.  
Enter one of the following commands:  
-1 printer test  
-2 plotter test  
-c change COM configuration  
-q quit  
?
A short explanation of each command is given in the following paragraphs.  
-1 printer test  
Select this test to verify the configuration of the GPIB-COM when connecting it to a GPIB ASCII  
printer. This test will send characters to the printer.  
Entering this command returns the prompt:  
Starting printer test.  
Press any key to stop printing.  
© National Instruments Corporation  
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GPIB-COM User Manual  
 
 
Running Diagnostic Tests  
Section Four  
The printer should begin printing a string of characters. To stop the test, press any key. The  
following message then appears:  
Printer test finished.  
Please check output to printer with user manual instructions.  
The output on the printer should read:  
NATIONAL INSTRUMENTS GPIB-COM DIAGNOSTIC TEST!"#$%&'()*+,-.  
/0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]_'abcdefghijkl  
mnopqrstuvwxyz{|}~ !"#$%&'()*+,./0123456789:;<=>?@ABCDEFGHI  
JKLMNOPQRSTUVWXY Z[\]_'abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'  
()*+,./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]_'abcdefghi  
jklmnopqrstuvwxyz{|}~ !"#$%&'()*+,./0123456789:;<=>?@ABCDEFG  
HIJKLMNOPQRSTUVWXYZ[\]_'abcdefghijklmnopqrstuvwxyz{|}~  
If the printer does not respond, an error message appears on the screen along with a message  
telling you to recheck all of your connections and jumper settings. If the test still fails after  
everything has been checked, write down the error message, if any, and call National Instruments.  
-2 plotter test  
Select this test to verify the configuration of the GPIB-COM when connecting it to a GPIB HP-GL  
plotter. This test will send output to the plotter.  
When this command is selected, the computer prints the following message:  
Starting plotter test.  
As illustrated in Figure 4-1, the plotter begins to draw four ovals.  
Figure 4-1. Plotter Output  
GPIB-COM User Manual  
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© National Instruments Corporation  
 
 
Section Four  
Running Diagnostic Tests  
When it is finished, the following message appears on the screen:  
Plotter test finished.  
Please check output to plotter with user manual instructions.  
If the plotter does not respond or the output on the plotter does not match Figure 4-1, check again  
to be sure that all of the connections are tight and the jumpers are all set correctly. Try the test  
again. If it still does not work, write down any error messages that appear and call National  
Instruments.  
-c change COM configuration  
This command is used to change the base address of the GPIB-COM to match the actual board  
settings. If you have changed the jumper settings to something different than the default settings,  
you must run this command.  
When this command is selected, the following menu appears:  
This program assumes the GPIB-COM is configured at base address  
3F8 (COM1).  
Enter the number of the correct address.  
1) base address 3F8 (COM1)  
2) base address 2F8 (COM2)  
Enter 1, 2, or <return> for no change?  
Type in the number of the address that you have configured the board to. The computer prints out  
your choice and returns to the main menu.  
-q quit  
This command ends the test program and returns to DOS.  
© National Instruments Corporation  
4-3  
GPIB-COM User Manual  
 
 
Section Five  
Programming the GPIB-COM  
This section presents a description of the GPIB-COM Serial Port Emulator registers and  
information on programming the GPIB-COM. You need to use this section only if you are  
writing your own serial port device driver.  
The GPIB-COM Registers  
IBM's serial adapter is a plug-in card for the PC that handles RS-232 communication. The main  
component of the adapter is an INS8250 Asynchronous Communications chip or its equivalent,  
which is controlled by programming a set of registers on the I/O channel. The names of these  
registers and their I/O addresses are given in Table 5-1. Each register is located at a certain offset  
from the base address of the board. The addresses are given with an X for the first digit and a Y  
for the second digit, where XY=3F for COM1 (base address 3F8), XY=2F for COM2 (base  
address 2F8), XY=3E for COM3 (base address 3E8), and XY=2E for COM4 (base address  
2E8). Notice that sometimes two registers share the same I/O address. The DLAB bit (bit 7 of  
the Line Control Register) determines which register will respond when these addresses are  
accessed.  
Note: Throughout this section, the term set will be used to mean that a bit is a logical 1, and clear  
will mean that the bit is a logical 0.  
Table 5-1. GPIB-COM Registers  
I/O Address  
Offset from  
Base Address  
Register  
Type  
XY=3F for COM1  
XY=2F for COM2  
XY=3E for COM3  
XY=2E for COM4  
Transmitter Holding Register  
Receive Buffer Register  
Divisor Latch LSB Register  
Divisor Latch MSB Register  
Interrupt Enable Register  
write  
read  
read/write  
read/write  
read/write  
XY8 (DLAB=0)  
XY8 (DLAB=0)  
XY8 (DLAB=1)  
XY9 (DLAB=1)  
XY9 (DLAB=0)  
XYA  
XYB  
XYC  
XYD  
XYE  
0
0
0
1
1
2
3
4
5
6
Interrupt Identification Register read  
Line Control Register  
Modem Control Register  
Line Status Register  
read/write  
read/write  
read  
Modem Status Register  
read  
The following pages describe the functions of each register on the serial adapter and on the GPIB-  
COM. For a more complete description of the serial adapter, refer to the IBM Options and  
Adapters Manual.  
© National Instruments Corporation  
5-1  
GPIB-COM User Manual  
 
 
Programming the GPIB-COM  
Section Five  
Transmitter Holding Register  
Offset from Base I/O Address = 0  
Register Address = XF8  
DLAB bit in Line Control Register = 0  
7
6
5
4
3
2
1
0
D7  
D6  
D5  
D4  
D2  
D1  
D0  
D3  
W
The Transmitter Holding Register contains the character to be sent to the serial output, with bit 0  
being the least significant and bit 7 the most significant. It functions identically on the GPIB-COM  
and the INS8250.  
Bit  
Mnemonic  
Description  
7-0w  
D[7-0]  
Data Bits 7 through 0  
GPIB-COM User Manual  
5-2  
© National Instruments Corporation  
 
 
Section Five  
Programming the GPIB-COM  
Receive Buffer Register  
Offset from Base I/O Address = 0  
Register Address = XF8  
DLAB bit in Line Control Register = 0  
7
6
5
4
3
2
1
0
R
D7  
D6  
D5  
D4  
D2  
D1  
D0  
D3  
The Receive Buffer Register contains the character received from the serial input, with bit 0 being  
the least significant and bit 7 the most significant. It functions identically on the GPIB-COM and  
the INS8250.  
Bit  
Mnemonic  
Description  
7-0r  
D[7-0]  
Data Bits 7 through 0  
© National Instruments Corporation  
5-3  
GPIB-COM User Manual  
 
 
Programming the GPIB-COM  
Section Five  
Divisor Latch Least Significant Byte (LSB) Register  
Offset from Base I/O Address = 0  
Register Address = XF8  
DLAB bit in Line Control Register = 1  
7
6
5
4
3
2
1
0
DL7  
DL6  
DL5  
DL4  
DL2  
DL1  
DL0  
R/W  
DL3  
Bit  
7-0r/w  
Mnemonic  
Description  
DL[7-0]  
Data Bits 7 through 0  
Divisor Latch Most Significant Byte (MSB) Register  
Offset from Base I/O Address = 1  
Register Address = XF9  
DLAB bit in Line Control Register = 1  
7
6
5
4
3
2
1
0
DL15  
DL14  
DL13  
DL12  
DL10  
DL9  
DL8  
R/W  
DL11  
The value stored in these two registers is used to determine the baud rate for serial communica-  
tions. The 16-bit number formed by the Divisor Latch LSB and MSB is divided into a 1.8432  
MHz clock to produce the baud rate.  
The Divisor Latch Registers are ignored by the GPIB-COM circuitry; however, they are available  
on the GPIB-COM and can be written to and read by software.  
Bit  
Mnemonic  
Description  
7-0r/w  
DL[15-8]  
Data Bits 15 through 8  
GPIB-COM User Manual  
5-4  
© National Instruments Corporation  
 
 
Section Five  
Programming the GPIB-COM  
Interrupt Enable Register  
Offset from Base I/O Address = 1  
Register Address = XF9  
DLAB bit in Line Control Register = 0  
7
0
6
0
5
0
4
0
3
2
1
0
R/W  
RLS  
THR  
RDA  
MS  
The Interrupt Enable Register is a read/write register that allows the programmer to selectively  
enable or disable each of the four possible types of interrupts generated by the INS8250. The high  
four bits are not used and are permanently cleared. The lower four bits each enable one type of  
interrupt as listed below.  
Bit  
Mnemonic  
Description  
7-4r/w  
0
Reserved Bits 7 through 4  
These bits always read as 0.  
Modem Status Interrupt Enable Bit  
3r/w  
MS  
This bit enables a modem status interrupt when set to logical 1.  
The modem status interrupt occurs when any of bits 0 through 3  
of the Modem Status Register are set to logical 1.  
This bit is identical on the GPIB-COM and the INS8250, but  
bits 0 through 3 of the Modem Status Register are set for  
different conditions as noted under the Modem Status Register  
description.  
2r/w  
RLS  
Receive Line Status Interrupt Enable Bit  
This bit enables a line status interrupt when set. The line status  
interrupt occurs when any of bits 1 through 4 of the Line Status  
Register become set.  
This bit is identical on the GPIB-COM and the INS8250, but  
bits 1 through 4 of the Line Status Register are set for different  
conditions as noted under the Line Status Register description.  
© National Instruments Corporation  
5-5  
GPIB-COM User Manual  
 
 
Programming the GPIB-COM  
Section Five  
Bit  
Mnemonic  
Description  
1r/w  
THR  
Transmitter Holding Register Interrupt Enable Bit  
This bit enables a transmitter holding register empty interrupt  
when set. The transmitter holding register empty interrupt  
occurs when the INS8250 becomes ready to send another  
character.  
This bit functions identically on the GPIB-COM and the  
INS8250.  
0r/w  
RDA  
Received Data Available Interrupt Enable Bit  
This bit enables a received data available interrupt when set. The  
received data available interrupt occurs when a character is  
received from the serial input and stored in the Receive Buffer  
Register.  
This bit functions identically on the GPIB-COM and the  
INS8250.  
GPIB-COM User Manual  
5-6  
© National Instruments Corporation  
 
Section Five  
Programming the GPIB-COM  
Interrupt Identification Register  
Offset from Base I/O Address = 2  
Register Address = XFA  
7
0
6
0
5
0
4
0
3
0
2
1
0
R
ID1  
ID0  
INT  
The Interrupt Identification Register is a read-only register which tells you when an interrupt is  
pending and if so, what kind of interrupt it is. This register functions identically on the GPIB-  
COM and the INS8250.  
Bit  
Mnemonic  
Description  
7-3r  
0
Reserved Bits 7 through 3  
These bits always read as 0.  
Identify Interrupt Register Bits  
2-1r  
ID[1-0]  
These two bits identify the interrupt that is pending. If more  
than one interrupt is pending, only the one with the highest  
priority is identified. The types and priorities are given in Table  
5-2.  
Table 5-2. Interrupt Types and Priorities  
Bit 2  
Bit 1  
Type of Interrupt  
Priority  
0
0
1
0
1
0
Receiver Line Status  
Received Data Available  
Transmitter Holding  
Register Empty  
1st  
2nd  
3rd  
4th  
1
1
Modem Status  
0r  
INT  
Interrupt Pending Bit  
This bit is clear if an interrupt is pending. If set, no interrupt is  
pending.  
© National Instruments Corporation  
5-7  
GPIB-COM User Manual  
 
 
Programming the GPIB-COM  
Section Five  
Line Control Register  
Offset from Base I/O Address = 3  
Register Address = XFB  
7
6
5
4
3
2
1
0
DLAB  
SBRK  
STP  
EVEN  
STB  
WL1  
WL0  
R/W  
PEN  
The Line Control Register is a read/write register that allows the programmer to set the RS-232  
parameters for the INS8250. The function of each bit in this register is explained below.  
Bit  
Mnemonic  
Description  
7r/w  
DLAB  
Divisor Latch Access Bit  
This bit controls which registers will respond to I/O addresses  
XF8 and XF9. This bit is set to access the Divisor Latch LSB  
and MSB, and cleared to access the Transmitter Holding  
Register, the Receive Buffer Register, and the Interrupt Enable  
Register.  
This bit functions identically on the GPIB-COM and the  
INS8250.  
6r/w  
5r/w  
SBRK  
STP  
Set Break Control Bit  
When set, this bit causes the SOUT line of the serial cable to be  
forced to a logical 0 state.  
This bit is ignored by the GPIB-COM.  
Stick Parity Bit  
When this bit is set, the parity bit transmitted and detected will  
be the inverse of the EVEN bit (bit 4), regardless of the number  
of 1's in the data word.  
This bit is ignored by the GPIB-COM.  
Even Parity Select Bit  
4r/w  
EVEN  
If this bit is set, even parity will be generated and checked. If  
this bit is clear, odd parity will be generated and checked.  
This bit is ignored by the GPIB-COM.  
GPIB-COM User Manual  
5-8  
© National Instruments Corporation  
 
 
Section Five  
Programming the GPIB-COM  
Bit  
Mnemonic  
Description  
3r/w  
PEN  
Parity Enable Bit  
If this bit is set, the INS8250 will generate and check parity  
according to the values of the STP and EVEN bits (bits 4 and  
5). If this bit is clear, the INS8250 will not generate or check  
parity bits.  
This bit is ignored by the GPIB-COM.  
Stop Bit Control Bit  
2r/w  
STB  
This bit controls the number of stop bits sent and verified by the  
INS8250. If this bit is set, two stop bits will be used. If this bit  
is clear, one stop bit will be used.  
This bit is ignored by the GPIB-COM.  
Word Length Select Bits  
1-0r/w  
WL[1-0]  
These two bits set the length of the words sent or received  
according to Table 5-3.  
Table 5-3. Word Length Select Bits  
Bit 1  
Bit 0  
Word Length  
0
0
1
1
0
1
0
1
5 bits  
6 bits  
7 bits  
8 bits  
These bits have no meaning on the GPIB and are ignored by the  
GPIB-COM circuitry.  
© National Instruments Corporation  
5-9  
GPIB-COM User Manual  
 
 
Programming the GPIB-COM  
Section Five  
Modem Control Register  
Offset from Base I/O Address = 4  
Register Address = XFC  
7
0
6
0
5
0
4
3
2
1
0
R/W  
LOOP  
OUT1  
RTS  
DTR  
OUT2  
The Modem Control Register is a read/write register that controls RS-232 output lines for  
communication with a modem or modem emulator. The function of each bit in this register is  
explained below.  
Bit  
Mnemonic  
Description  
7-5r/w  
0
Reserved Bits 7 through 5  
These bits always read as 0.  
Loopback Diagnostic Test Bit  
4r/w  
3r/w  
LOOP  
OUT2  
When set, this bit internally connects the outputs of the INS8250  
back to the inputs to allow the chip to be tested by writing data to  
itself and reading it back for verification.  
This bit is ignored by the GPIB-COM circuitry.  
Auxiliary Output 2 Bit  
The OUT2 serial port output is the inverse of this bit. All  
interrupts from the serial adapter are disabled when this bit is  
cleared.  
When this bit is cleared, interrupts are disabled on the GPIB-  
COM.  
2r/w  
1r/w  
OUT1  
RTS  
Auxiliary Output 1 Bit  
The OUT1 serial port output is the inverse of this bit.  
This bit is ignored by the GPIB-COM circuitry.  
Request to Send Bit  
The RTS serial port output is the inverse of this bit. When this  
bit is set, it indicates that the Controller is ready to send data.  
On the GPIB-COM, this bit is used along with the DTR bit to  
control the CTS bit of the Modem Status Register.  
GPIB-COM User Manual  
5-10  
© National Instruments Corporation  
 
 
Section Five  
Programming the GPIB-COM  
Bit  
Mnemonic  
Description  
0r/w  
DTR  
Data Terminal Ready Bit  
The DTR serial port output is the inverse of this bit. This bit is  
set when the Controller is ready to communicate.  
On the GPIB-COM, this bit is used along with the RTS bit to  
control the CTS bit of the Modem Status Register.  
© National Instruments Corporation  
5-11  
GPIB-COM User Manual  
 
Programming the GPIB-COM  
Section Five  
Line Status Register  
Offset from Base I/O Address = 5  
Register Address = XFD  
7
0
6
5
4
3
2
1
0
R
TEMT  
THRE  
BI  
PE  
OE  
DR  
FE  
The Line Status Register provides information about the status of the data transfer. On the GPIB-  
COM this register is implemented as a read-only register. Writing to the line status register will  
not change its contents. The function of each bit in this register is explained below.  
Bit  
Mnemonic  
Description  
7r  
0
Reserved Bit  
This bit always reads as 0.  
Transmitter Shift Register Empty Bit  
6r  
5r  
4r  
TEMT  
THRE  
BI  
This bit is cleared when a character is transferred from the  
Transmitter Holding Register to the Transmitter Shift Register  
and set when the character has been shifted out of the Shift  
Register onto the serial output line.  
On the GPIB-COM, there is no shift register so this bit behaves  
exactly the same as the THRE bit.  
Transmitter Holding Register Empty Bit  
This bit is cleared when the processor writes a character into the  
Transmitter Holding Register and set when the character has  
been transmitted and the INS8250 is ready to send another  
character.  
This bit functions identically on the GPIB-COM and the  
INS8250.  
Break Interrupt Bit  
This bit is set to logical 1 when the serial data input remains in  
the logical 0 state for longer than one full word transmission  
time.  
On the GPIB-COM, this bit is always clear.  
GPIB-COM User Manual  
5-12  
© National Instruments Corporation  
 
 
Section Five  
Programming the GPIB-COM  
Bit  
Mnemonic  
Description  
3r  
FE  
Framing Error Bit  
This bit is set when the received character does not have a valid  
stop bit.  
On the GPIB-COM, this bit is always clear.  
Parity Error Bit  
2r  
PE  
This bit is set when the received character does not have the  
correct parity. It is cleared when the processor reads the Line  
Status Register.  
On the GPIB-COM, this bit is set when the SRQ* line of the  
GPIB is asserted. When the special function selection DIP  
switch has been set to disable the SRQ feature, this bit is always  
clear.  
1r  
OE  
Overrun Error Bit  
This bit is set when a new character is received and stored in the  
Receive Buffer Register before the processor reads the previous  
character, thus overwriting and destroying the previous  
character. It is cleared when the processor reads the Line Status  
Register.  
On the GPIB-COM, this bit is always clear.  
Data Ready Bit  
0r  
DR  
This bit is set when a character has been received and stored in  
the Receive Buffer Register. It is cleared when the processor  
reads the Receive Buffer Register.  
This bit functions identically on the GPIB-COM and the  
INS8250.  
© National Instruments Corporation  
5-13  
GPIB-COM User Manual  
 
Programming the GPIB-COM  
Section Five  
Modem Status Register  
Offset from Base I/O Address = 6  
Register Address = XFE  
7
6
5
4
3
2
1
0
R
DCD  
RI  
DSR  
CTS  
DDCD  
TERI  
DDSR  
DCTS  
The Modem Status Register gives the state of the modem control lines and tells whether any of  
these lines have changed state since the register was last read. This register is read only on the  
GPIB-COM. Writing to this register will not change its contents. The function of each bit in this  
register is explained below.  
Bit  
Mnemonic  
Description  
7r  
DCD  
Data Carrier Detect Bit  
This bit reflects the inverse of the serial port DCD input signal.  
On the GPIB-COM, this bit is always clear.  
Ring Indicator Bit  
6r  
5r  
RI  
This bit reflects the inverse of the serial port RI input signal.  
On the GPIB-COM, this bit is always clear.  
Data Set Ready Bit  
DSR  
This bit reflects the inverse of the serial port DSR input signal.  
On the GPIB-COM, this bit is always set to indicate that the  
interface is ready to transfer data.  
4r  
3r  
CTS  
Clear to Send Bit  
This bit reflects the inverse of the serial port CTS input signal.  
On the GPIB-COM, this bit is the logical AND of the DTR and  
RTS bits of the Modem Control Register.  
DDCD  
Delta Data Carrier Detect Bit  
This bit is set when the serial port DCD input signal changes  
state and cleared when the processor reads the Modem Status  
Register.  
On the GPIB-COM, this bit is always clear.  
GPIB-COM User Manual  
5-14  
© National Instruments Corporation  
 
 
Section Five  
Programming the GPIB-COM  
Bit  
Mnemonic  
Description  
2r  
TERI  
Trailing Edge Ring Indicator Bit  
This bit is set when the serial port RI input signal changes from  
a logical 1 to a logical 0 and cleared when the processor reads  
the Modem Status Register.  
On the GPIB-COM, this bit is always clear.  
Delta Set Ready Bit  
1r  
0r  
DDSR  
DCTS  
This bit is set when the serial port DSR input signal changes  
state and cleared when the processor reads the Modem Status  
Register.  
On the GPIB-COM, this bit is always clear.  
Delta Clear to Send Bit  
This bit is set when the CTS input changes state and cleared  
when the processor reads the Modem Status Register.  
On the GPIB-COM, this bit is the logical AND of the DTR and  
RTS bits of the Modem Control Register.  
© National Instruments Corporation  
5-15  
GPIB-COM User Manual  
 
Programming the GPIB-COM  
Section Five  
Programming the Serial Adapter  
The operation of the serial adapter is controlled by software, either IBM BIOS or an application.  
To transfer data to and from the serial port, the communications parameters must first be set up in  
the following manner:  
1. Load the baud rate divisor into the divisor latch.  
2. Store the RS-232 parameters in the Line Control Register.  
3. Send the modem control signals by writing to the Modem Control Register.  
4. Enable interrupts, if used, by writing to the appropriate bits in the Interrupt Enable Register.  
Once the control registers have been programmed correctly, the software can transmit and receive  
serial data by polling, interrupts, or both.  
Polling Method  
In the polled method of operation, the Line Status Register is continuously read to check if the Data  
Ready Bit is set. When this bit becomes set, the Receive Buffer Register is read to get the  
character that just came from the serial port, and the process continues. To transmit data, the Line  
Status Register is polled until the Transmitter Holding Register Empty Bit is set. A byte can then  
be written to the Transmitter Holding Register, and polling continues.  
Interrupt-Driven Method  
In the interrupt-driven mode of operation, the desired interrupts are enabled through the OUT2 bit  
and the Interrupt Enable Register. An interrupt handler is installed to respond when an interrupt  
occurs. Software processes can perform other tasks until an interrupt is received. When an  
interrupt occurs, the handler reads the Interrupt Identification Register to determine the type of  
interrupt and takes appropriate action, such as reading the Receive Buffer Register in the case of a  
received data available interrupt, writing to the Transmitter Holding Register if it was a THRE  
interrupt, or printing an error message in the case of a line status interrupt.  
GPIB-COM User Manual  
5-16  
© National Instruments Corporation  
 
 
Section Five  
Programming the GPIB-COM  
The GPIB-COM Controller Function  
Because most serial port applications involve communication with only one serial line, the GPIB-  
COM imposes some restrictions on the GPIB in order to be compatible with existing serial port  
software. The GPIB-COM must be System Controller of the GPIB and will not work with other  
Controllers. The behavior of the GPIB-COM depends on the setting of the talk-only jumper.  
If the jumper is set to talk-only, the GPIB-COM assumes that there is a listen-only device  
connected to the GPIB. When a byte is written into the Transmitter Holding Register, the GPIB-  
COM sets the THRE bit of the Line Status Register to 0, puts the contents of that register on the  
GPIB data lines, and begins the source handshake sequence. When the Listener releases NDAC*,  
the THRE bit is set back to 1 and the GPIB-COM waits for another byte to be written into the  
Transmitter Holding Register.  
If the jumper is set to talk/listen, the GPIB-COM assumes that the device connected to the GPIB  
can be addressed to listen or talk. When the computer is powered on, the GPIB-COM sends the  
talk address that is set on the DIP switches, addresses itself as a Listener, and unasserts NRFD*.  
If the GPIB device sends a byte, the GPIB-COM accepts it, stores it in the Receive Buffer  
Register, and sets the DR bit of the Line Status Register. At the end of the GPIB handshake, it  
keeps NRFD* asserted until the computer reads the byte from the Receive Buffer Register.  
If the computer writes a byte to the Transmitter Holding Register, the GPIB-COM sends the GPIB  
device its listen address from the DIP switches and addresses itself to talk. Then it sends the byte  
to the GPIB device, which is now addressed as a Listener. When the GPIB-COM begins a source  
handshake, it starts a 200-msec timer. If the source handshake is completed before the 200 msec  
is expired, the GPIB-COM remains addressed to talk until the timer runs out. If the computer  
writes another byte before the timer runs out, the GPIB-COM restarts the timer and sends the byte.  
When 200 msec has passed since the last byte was written, the GPIB-COM sends the talk address  
and addresses itself to listen again. If a byte was waiting in the Receive Buffer Register when the  
computer wrote to the Transmitter Holding Register, the GPIB-COM remembers this and when it  
becomes a Listener again, it asserts NRFD* until the computer reads the byte from the Receive  
Buffer Register.  
© National Instruments Corporation  
5-17  
GPIB-COM User Manual  
 
 
Appendix A  
Specifications  
This appendix lists the specifications of the GPIB-COM board.  
Power Requirement  
+5 VDC (± 5%)  
0.75 A typical  
Physical  
Dimensions  
4.2 in. by 8.75 in.  
I/O Connector  
IEEE-488 Standard 24-pin  
Operating Environment  
Component Temperature  
Relative Humidity  
Emissions  
0° to 70° C  
5% to 90%, noncondensing  
FCC Class B  
Storage Environment  
Temperature  
-55° to 125° C  
Relative Humidity  
5% to 90%, noncondensing  
© National Instruments Corporation  
A-1  
GPIB-COM User Manual  
 
 
Appendix B  
Multiline Interface Command Messages  
The following tables are multiline interface messages (sent and received with ATN TRUE).  
© National Instruments Corporation  
B-1  
GPIB-COM User Manual  
 
 
Multiline Interface Command Messages  
Appendix B  
Multiline Interface Messages  
Hex Oct Dec ASCII Msg  
Hex Oct Dec ASCII Msg  
00  
01  
02  
03  
04  
05  
06  
07  
000  
001  
002  
003  
004  
005  
006  
007  
0
1
2
3
4
5
6
7
NUL  
SOH  
STX  
ETX  
EOT  
ENQ  
ACK  
BEL  
20  
21  
22  
23  
24  
25  
26  
27  
040  
041  
042  
043  
044  
045  
046  
047  
32  
33  
34  
35  
36  
37  
38  
39  
SP  
!
"
#
$
%
&
'
MLA0  
MLA1  
MLA2  
MLA3  
MLA4  
MLA5  
MLA6  
MLA7  
GTL  
SDC  
PPC  
08  
09  
010  
011  
012  
013  
014  
015  
016  
017  
8
9
BS  
HT  
LF  
VT  
FF  
CR  
SO  
SI  
GET  
TCT  
28  
29  
050  
051  
052  
053  
054  
055  
056  
057  
40  
41  
42  
43  
44  
45  
46  
47  
(
)
*
+
,
-
.
MLA8  
MLA9  
0A  
0B  
0C  
0D  
0E  
0F  
10  
11  
12  
13  
14  
15  
2A  
2B  
2C  
2D  
2E  
2F  
MLA10  
MLA11  
MLA12  
MLA13  
MLA14  
MLA15  
/
10  
11  
12  
13  
14  
15  
16  
17  
020  
021  
022  
023  
024  
025  
026  
027  
16  
17  
18  
19  
20  
21  
22  
23  
DLE  
DC1  
DC2  
DC3  
DC4  
NAK  
SYN  
ETB  
30  
31  
32  
33  
34  
35  
36  
37  
060  
061  
062  
063  
064  
065  
066  
067  
48  
49  
50  
51  
52  
53  
54  
55  
0
1
2
3
4
5
6
7
MLA16  
MLA17  
MLA18  
MLA19  
MLA20  
MLA21  
MLA22  
MLA23  
LLO  
DCL  
PPU  
18  
19  
030  
031  
032  
033  
034  
035  
036  
037  
24  
25  
26  
27  
28  
29  
30  
31  
CAN  
EM  
SUB  
ESC  
FS  
GS  
RS  
SPE  
SPD  
38  
39  
070  
071  
072  
073  
074  
075  
076  
077  
56  
57  
58  
59  
60  
61  
62  
63  
8
9
:
MLA24  
MLA25  
MLA26  
MLA27  
MLA28  
MLA29  
MLA30  
UNL  
1A  
1B  
1C  
1D  
1E  
1F  
3A  
3B  
3C  
3D  
3E  
3F  
;
<
=
>
?
US  
Message Definitions  
DCL  
GET  
GTL  
LLO  
Device Clear  
Group Execute Trigger  
Go To Local  
MSA My Secondary Address  
MTA My Talk Address  
PPC  
PPD  
Parallel Poll Configure  
Parallel Poll Disable  
Local Lockout  
MLA My Listen Address  
GPIB-COM User Manual  
B-2  
© National Instruments Corporation  
 
Appendix B  
Multiline Interface Command Messages  
Multiline Interface Messages  
Hex Oct Dec ASCII Msg  
Hex Oct Dec ASCII Msg  
40  
41  
42  
43  
44  
45  
46  
47  
100  
101  
102  
103  
104  
105  
106  
107  
64  
65  
66  
67  
68  
69  
70  
71  
@
A
B
C
D
E
MTA0  
MTA1  
MTA2  
MTA3  
MTA4  
MTA5  
MTA6  
MTA7  
60  
61  
62  
63  
64  
65  
66  
67  
140  
141  
142  
143  
144  
145  
146  
147  
96  
97  
98  
`
MSA0,PPE  
MSA1,PPE  
MSA2,PPE  
MSA3,PPE  
MSA4,PPE  
MSA5,PPE  
MSA6,PPE  
MSA7,PPE  
a
b
c
d
e
f
99  
100  
101  
102  
103  
F
G
g
48  
49  
110  
111  
112  
113  
114  
115  
116  
117  
72  
73  
74  
75  
76  
77  
78  
79  
H
I
J
K
L
M
N
O
MTA8  
MTA9  
68  
69  
150  
151  
152  
153  
154  
155  
156  
157  
104  
105  
106  
107  
108  
109  
110  
111  
h
i
j
k
l
m
n
o
MSA8,PPE  
MSA9,PPE  
MSA10,PPE  
MSA11,PPE  
MSA12,PPE  
MSA13,PPE  
MSA14,PPE  
MSA15,PPE  
4A  
4B  
4C  
4D  
4E  
4F  
MTA10  
MTA11  
MTA12  
MTA13  
MTA14  
MTA15  
6A  
6B  
6C  
6D  
6E  
6F  
50  
51  
52  
53  
54  
55  
56  
57  
120  
121  
122  
123  
124  
125  
126  
127  
80  
81  
82  
83  
84  
85  
86  
87  
P
MTA16  
MTA17  
MTA18  
MTA19  
MTA20  
MTA21  
MTA22  
MTA23  
70  
71  
72  
73  
74  
75  
76  
77  
160  
161  
162  
163  
164  
165  
166  
167  
112  
113  
114  
115  
116  
117  
118  
119  
p
q
r
s
t
u
v
w
MSA16,PPD  
MSA17,PPD  
MSA18,PPD  
MSA19,PPD  
MSA20,PPD  
MSA21,PPD  
MSA22,PPD  
MSA23,PPD  
Q
R
S
T
U
V
W
58  
59  
130  
131  
132  
133  
134  
135  
136  
137  
88  
89  
90  
91  
92  
93  
94  
95  
X
Y
Z
[
\
]
MTA24  
MTA25  
MTA26  
MTA27  
MTA28  
MTA29  
MTA30  
UNT  
78  
79  
170  
171  
172  
173  
174  
175  
176  
177  
120  
121  
122  
123  
124  
125  
126  
127  
x
y
z
{
|
}
MSA24,PPD  
MSA25,PPD  
MSA26,PPD  
MSA27,PPD  
MSA28,PPD  
MSA29,PPD  
MSA30,PPD  
5A  
5B  
5C  
5D  
5E  
5F  
7A  
7B  
7C  
7D  
7E  
7F  
^
_
~
DEL  
PPE  
PPU  
SDC  
SPD  
Parallel Poll Enable  
Parallel Poll Unconfigure  
Selected Device Clear  
Serial Poll Disable  
SPE  
Serial Poll Enable  
Take Control  
Unlisten  
TCT  
UNL  
UNT  
Untalk  
© National Instruments Corporation  
B-3  
GPIB-COM User Manual  
 
Appendix C  
Operation of the GPIB  
History of the GPIB  
The GPIB is a link, bus, or interface system through which interconnected electronic devices  
communicate. Hewlett-Packard invented the GPIB, which they call the HP-IB, to connect and  
control programmable instruments manufactured by them. Because of its high system data rate  
ceilings of from 250 kbytes/sec to 1 Mbyte/sec, the GPIB quickly became popular in other  
applications such as intercomputer communication and peripheral control. It was later accepted as  
the industry standard IEEE-488. The versatility of the system prompted the name General  
Purpose Interface Bus.  
Types of Messages  
Devices on the GPIB communicate by passing messages through the interface system. There are  
two types of messages:  
Device-dependent messages, often called data or data messages, contain device-specific  
information such as programming instructions, measurement results, machine status, and data  
files.  
Interface messages manage the bus itself. They are usually called commands or command  
messages. Interface messages perform such functions as initializing the bus, addressing and  
unaddressing devices, and setting devices for remote or local programming.  
Note: The term command as used here should not be confused with some device instructions  
which are also called commands. Such device-specific instructions are actually data  
messages.  
Talkers, Listeners, and Controllers  
There are three types of GPIB communicators. A Talker sends data messages to one or more  
Listeners. The Controller manages the flow of information on the GPIB by sending commands to  
all devices.  
Devices can be Talkers, Listeners, and/or Controllers. A digital multimeter, for example, is a  
Talker and may also be a Listener. A printer or plotter is usually only a Listener. A computer on  
the GPIB often combines all three roles to manage the bus and communicate with other devices.  
The GPIB is a bus like a typical computer bus except that the computer has its circuit cards  
interconnected via a backplane bus whereas the GPIB has standalone devices interconnected via a  
cable bus.  
The role of the GPIB Controller can also be compared to the role of the computer's CPU, but a  
better analogy is to the switching center of a city telephone system.  
The switching center (Controller) monitors the communications network (GPIB). When the  
center (Controller) notices that a party (device) wants to make a call (send a data message), it  
connects the caller (Talker) to the receiver (Listener).  
© National Instruments Corporation  
C-1  
GPIB-COM User Manual  
 
 
Operation of the GPIB  
Appendix C  
The Controller usually addresses a Talker and a Listener before the Talker can send its message to  
the Listener. After the message is transmitted, the Controller usually unaddresses both devices.  
Some bus configurations do not require a Controller. For example, one device may only be a  
Talker (called a talk-only device) and there may be one or more listen-only devices.  
A Controller is necessary when the active or addressed Talker or Listener must be changed. The  
Controller function is usually handled by a computer.  
System Controller and Active Controller  
Although there can be multiple Controllers on the GPIB, only one Controller at a time is Active  
Controller or Controller-in-Charge. Active control can be passed from the current Active  
Controller to an idle Controller. Only one device on the bus, the System Controller, can make  
itself the Active Controller.  
GPIB Signals  
The interface bus consists of 16 signal lines and 8 ground return or shield drain lines. The 16  
signal lines are divided into three groups:  
eight data lines  
three handshake lines  
five interface management lines  
GPIB-COM User Manual  
C-2  
© National Instruments Corporation  
 
 
Appendix C  
Operation of the GPIB  
Figure C-1 shows the arrangement of these signals on the GPIB cable connector.  
1
2
3
4
5
6
7
8
9
13  
14  
15  
16  
17  
18  
19  
20  
21  
DIO1*  
DIO2*  
DIO3*  
DIO4*  
EOI*  
DAV*  
NRFD*  
NDAC*  
IFC*  
DIO5*  
DIO6*  
DIO7*  
DIO8*  
REN*  
GND (TW PAIR W/DAV*)  
GND (TW PAIR W/NRFD*)  
GND (TW PAIR W/NDAC*)  
GND (TW PAIR W/IFC*)  
GND (TW PAIR W/SRQ*)  
GND (TW PAIR W/ATN*)  
SIGNAL GROUND  
10 22  
11 23  
12 24  
SRQ*  
ATN*  
SHIELD  
Figure C-1. GPIB Cable Connector  
Data Lines  
The eight data lines, DIO1 through DIO8, carry both data and command messages. All  
commands and most data use the 7-bit ASCII or ISO code set, in which case the eighth bit, DIO8,  
is unused or used for parity.  
Handshake Lines  
Three lines asynchronously control the transfer of message bytes among devices. The process is  
called a three-wire interlocked handshake and it guarantees that message bytes on the data lines are  
sent and received without transmission error.  
NRFD (not ready for data)  
NRFD indicates when a device is ready or not ready to receive a message byte. The line is driven  
by all devices when receiving commands and by Listeners when receiving data messages.  
NDAC (not data accepted)  
NDAC indicates when a device has or has not accepted a message byte. The line is driven by all  
devices when receiving commands and by Listeners when receiving data messages.  
© National Instruments Corporation  
C-3  
GPIB-COM User Manual  
 
 
Operation of the GPIB  
Appendix C  
DAV (data valid)  
DAV tells when the signals on the data lines are stable (valid) and can be accepted safely by  
devices. The Controller drives DAV when sending commands, and the Talker drives it when  
sending data messages.  
The way in which NRFD and NDAC are used by the receiving device is called the Acceptor  
Handshake. Likewise, the sending device uses DAV in the Source Handshake.  
Interface Management Lines  
Five lines are used to manage the flow of information across the interface.  
ATN (attention)  
The Controller drives ATN true when it uses the data lines to send commands and false when it  
allows a Talker to send data messages.  
IFC (interface clear)  
The System Controller drives the IFC line to initialize the bus to become Controller-In-Charge.  
REN (remote enable)  
The System Controller drives the REN line, which is used to place devices in remote or local  
program mode.  
SRQ (service request)  
Any device can drive the SRQ line to asynchronously request service from the Active Controller.  
EOI (end or identify)  
The EOI line has two purposes. The Talker uses the EOI line to mark the end of a message string.  
The Active Controller uses the EOI line to tell devices to identify their responses in a parallel poll.  
GPIB-COM User Manual  
C-4  
© National Instruments Corporation  
 
 
Appendix C  
Operation of the GPIB  
Physical and Electrical Characteristics  
Devices are usually connected with a cable assembly consisting of a shielded 24-conductor cable  
with both a plug and receptacle at each end. This design enables devices to be connected in either a  
linear or a star configuration, or a combination of the two. See Figures C-2 and C-3.  
Figure C-2. Linear Configuration of the GPIB Devices  
© National Instruments Corporation  
C-5  
GPIB-COM User Manual  
 
 
Operation of the GPIB  
Appendix C  
Figure C-3. Star Configuration of GPIB Devices  
The standard connector is the Amphenol or Cinch Series 57 MICRORIBBON or AMP CHAMP  
type. An adapter cable using non-standard cable and/or connector is used for special interconnect  
applications.  
The GPIB uses negative logic with standard TTL logic levels. When DAV is true, for example, it  
is a TTL low level (0.8 V), and when DAV is false, it is a TTL high level (2.0 V).  
GPIB-COM User Manual  
C-6  
© National Instruments Corporation  
 
 
Appendix C  
Operation of the GPIB  
Configuration Restrictions  
To achieve the high data transfer rate that the GPIB is designed for, the physical distance between  
devices and the number of devices on the bus is limited.  
The following restrictions are typical:  
A maximum separation of 4 m between any two devices and an average separation of 2 m  
over the entire bus.  
A maximum total cable length of 20 m.  
No more than 15 devices connected to each bus, with at least two-thirds powered-on.  
© National Instruments Corporation  
C-7  
GPIB-COM User Manual  
 
 
User Comment Form  
National Instruments encourages you to comment on the documentation supplied with our  
products. This information helps us provide quality products to meet your needs.  
Title: GPIB-COM User Manual  
Edition Date  
Part Number:  
June 1990  
320197-01  
Please comment on the completeness, clarity, and organization of the manual.  
If you find errors in the manual, please record the page numbers and describe the errors.  
Thank you for your help.  
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Address  
Phone  
(
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Mail to: Technical Publications  
National Instruments Corporation  
6504 Bridge Point Parkway, MS 53-02  
Austin, TX 78730-5039  
 

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