Black Box TV Converter Box IC026AE R2 User Manual

MARCH 1998  
IC026A-R2  
IC026AE-R2  
RS-232IEEE 488  
Interface Converter  
POWER  
ERROR  
SRQ  
LISTEN  
ALK  
T
CUSTOMER Order toll-free in the U.S. 24 hours, 7 A.M. Monday to midnight Friday: 877-877-BBOX  
FREE technical support, 24 hours a day, 7 days a week: Call 724-746-5500 or fax 724-746-0746  
Mail order: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018  
SUPPORT  
INFORMATION  
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WARNING!  
Noted conditions pertain to potential safety hazards. When you see a  
WARNING!, CAUTION!, or IMPORTANT! note, carefully read the  
information and be alert to the possibility of personal injury.  
Failure to follow these directives voids emission and immunity compliance.  
TRADEMARKS USED IN THIS MANUAL  
®
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AT , IBM , and PS/2 are registered trademarks, and PC/XT is a trademark,  
of IBM Corporation.  
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Macintosh is a registered trademark of Apple Computer, Inc.  
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Hewlett-Packard , HP , and HP-GL are registered trademarks of Hewlett-Packard.  
®
AutoCAD is a registered trademark of AUTODESK, Inc.  
®
MacPlot is a registered trademark of Microspot Ltd.  
All applied-for and registered trademarks are the property of their respective owners.  
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RS-232IEEE 488 INTERFACE CONVERTER  
FEDERAL COMMUNICATIONS COMMISSION  
AND  
INDUSTRY CANADA  
RADIO FREQUENCY INTERFERENCE STATEMENTS  
This equipment generates, uses, and can radiate radio frequency energy  
and if not installed and used properly, that is, in strict accordance with the  
manufacturer’s instructions, may cause interference to radio communication.  
It has been tested and found to comply with the limits for a Class A computing  
device in accordance with the specifications in Subpart J of Part 15 of FCC  
rules, which are designed to provide reasonable protection against such  
interference when the equipment is operated in a commercial environment.  
Operation of this equipment in a residential area is likely to cause interference,  
in which case the user at his own expense will be required to take whatever  
measures may be necessary to correct the interference.  
Changes or modifications not expressly approved by the party responsible  
for compliance could void the user’s authority to operate the equipment.  
This digital apparatus does not exceed the Class A limits for radio noise emission from  
digital apparatus set out in the Radio Interference Regulation of Industry Canada.  
Le présent appareil numérique n’émet pas de bruits radioélectriques dépassant les limites  
applicables aux appareils numériques de classe A prescrites dans le Règlement sur le  
brouillage radioélectrique publié par Industrie Canada.  
4
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NOM STATEMENT  
NORMAS OFICIALES MEXICANAS (NOM)  
ELECTRICAL SAFETY STATEMENT  
INSTRUCCIONES DE SEGURIDAD  
1. Todas las instrucciones de seguridad y operación deberán ser leídas  
antes de que el aparato eléctrico sea operado.  
2. Las instrucciones de seguridad y operación deberán ser guardadas para  
referencia futura.  
3. Todas las advertencias en el aparato eléctrico y en sus instrucciones  
de operación deben ser respetadas.  
4. Todas las instrucciones de operación y uso deben ser seguidas.  
5. El aparato eléctrico no deberá ser usado cerca del agua—por ejemplo,  
cerca de la tina de baño, lavabo, sótano mojado o cerca de una alberca,  
etc..  
6. El aparato eléctrico debe ser usado únicamente con carritos o pedestales  
que sean recomendados por el fabricante.  
7. El aparato eléctrico debe ser montado a la pared o al techo sólo como  
sea recomendado por el fabricante.  
8. Servicio—El usuario no debe intentar dar servicio al equipo eléctrico más  
allá a lo descrito en las instrucciones de operación. Todo otro servicio  
deberá ser referido a personal de servicio calificado.  
9. El aparato eléctrico debe ser situado de tal manera que su posición no  
interfiera su uso. La colocación del aparato eléctrico sobre una cama,  
sofá, alfombra o superficie similar puede bloquea la ventilación, no se  
debe colocar en libreros o gabinetes que impidan el flujo de aire por  
los orificios de ventilación.  
10. El equipo eléctrico deber ser situado fuera del alcance de fuentes de  
calor como radiadores, registros de calor, estufas u otros aparatos  
(incluyendo amplificadores) que producen calor.  
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RS-232IEEE 488 INTERFACE CONVERTER  
11. El aparato eléctrico deberá ser connectado a una fuente de poder sólo  
del tipo descrito en el instructivo de operación, o como se indique en  
el aparato.  
12. Precaución debe ser tomada de tal manera que la tierra fisica y la  
polarización del equipo no sea eliminada.  
13. Los cables de la fuente de poder deben ser guiados de tal manera que no  
sean pisados ni pellizcados por objetos colocados sobre o contra ellos,  
poniendo particular atención a los contactos y receptáculos donde salen  
del aparato.  
14. El equipo eléctrico debe ser limpiado únicamente de acuerdo a las  
recomendaciones del fabricante.  
15. En caso de existir, una antena externa deberá ser localizada lejos  
de las lineas de energia.  
16. El cable de corriente deberá ser desconectado del cuando el equipo  
no sea usado por un largo periodo de tiempo.  
17. Cuidado debe ser tomado de tal manera que objectos liquidos no sean  
derramados sobre la cubierta u orificios de ventilación.  
18. Servicio por personal calificado deberá ser provisto cuando:  
A: El cable de poder o el contacto ha sido dañado; u  
B: Objectos han caído o líquido ha sido derramado dentro del  
aparato; o  
C: El aparato ha sido expuesto a la lluvia; o  
D: El aparato parece no operar normalmente o muestra un cambio  
en su desempeño; o  
E: El aparato ha sido tirado o su cubierta ha sido dañada.  
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CONTENTS  
Contents  
Chapter  
Page  
1. Specifications..................................................................................................10  
2. Introduction ...................................................................................................12  
2.1 Description ............................................................................................12  
2.2 Abbreviations.........................................................................................13  
3. Getting Started ...............................................................................................14  
3.1 Inspection ..............................................................................................14  
3.2 Configuration ........................................................................................14  
3.3 Serial Port Settings ................................................................................16  
3.3.1 Serial Baud Rate ........................................................................16  
3.3.2 Serial Word Length (Data Bits)................................................18  
3.3.3 Serial Stop Bits...........................................................................18  
3.3.4 Serial Parity ................................................................................19  
3.3.5 Serial Echo .................................................................................19  
3.3.6 Serial Handshake.......................................................................20  
3.4 Selecting Terminator Substitution.......................................................21  
3.4.1 Serial Terminator ......................................................................21  
3.4.2 IEEE Bus Terminator ................................................................22  
3.5 Selecting the Mode ...............................................................................22  
3.6 Selecting the IEEE Address ..................................................................23  
3.7 Feature Selections .................................................................................24  
3.7.1 Controller Features ...................................................................24  
3.7.2 Peripheral Features ...................................................................25  
3.8 Serial Interface ......................................................................................25  
3.8.1 RS-232/RS-422 Signal Level Selection .....................................26  
3.8.2 Serial Signal Descriptions..........................................................26  
3.8.3 Serial-Cable Wiring Diagrams...................................................29  
3.9 General Operation................................................................................30  
4. Controller Operation.....................................................................................32  
4.1 Controller-Mode (Serial to IEEE) Operation .....................................32  
4.2 Serial and IEEE Terminator Substitution............................................33  
4.3 IEEE Address Selection.........................................................................34  
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RS-232IEEE 488 INTERFACE CONVERTER  
Chapter  
Page  
4.4 Talk-Back Features ................................................................................34  
4.4.1 Talk-Back on Terminator..........................................................34  
4.4.2 Talk-Back on Timeout...............................................................36  
4.5 Plotter Applications...............................................................................38  
4.6 Printer Applications ..............................................................................44  
5. Peripheral Operation.....................................................................................45  
5.1 Peripheral-Mode Operation .................................................................45  
5.2 Serial and IEEE Input Buffers ..............................................................45  
5.3 IEEE Data Transfers..............................................................................46  
5.3.1 Blind Bus Data Transfers...........................................................46  
5.3.2 Controlled Bus Data Transfers .................................................47  
5.4 Serial-Poll Status-Byte Register .............................................................48  
5.5 Use of Serial and Bus Terminators ......................................................50  
5.6 IEEE 488 Bus Implementation.............................................................50  
5.6.1 My Talk Address (MTA)............................................................51  
5.6.2 My Listen Address (MLA).........................................................51  
5.6.3 Device Clear (DCL and SDC)...................................................51  
5.6.4 Interface Clear (IFC).................................................................51  
5.6.5 Serial Poll Enable (SPE)............................................................51  
5.6.6 Serial Poll Disable (SPD) ..........................................................51  
5.6.7 Unlisten (UNL) .........................................................................51  
5.6.8 Untalk (UNT)............................................................................51  
5.7 IEEE Address Selection.........................................................................52  
6. IEEE 488 Primer.............................................................................................53  
6.1 History....................................................................................................53  
6.2 General Structure..................................................................................53  
6.3 Send It To My Address..........................................................................55  
6.4 Bus Management Lines.........................................................................56  
6.4.1 Attention (ATN)........................................................................56  
6.4.2 Interface Clear (IFC).................................................................56  
6.4.3 Remote Enable (REN) ..............................................................56  
6.4.4 End Or Identify (EOI) ..............................................................56  
6.4.5 Service Request (SRQ)..............................................................56  
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CONTENTS  
Chapter  
Page  
6.5 Handshake Lines...................................................................................57  
6.5.1 Data Valid (DAV).......................................................................57  
6.5.2 Not Ready For Data (NRFD) ....................................................57  
6.5.3 Not Data Accepted (NDAC) .....................................................57  
6.6 Data Lines..............................................................................................58  
6.7 Multiline Commands ............................................................................58  
6.7.1 Go To Local (GTL) ...................................................................58  
6.7.2 Listen Address Group (LAG)....................................................58  
6.7.3 Unlisten (UNL) .........................................................................59  
6.7.4 Talk Address Group (TAG) ......................................................59  
6.7.5 Untalk (UNT)............................................................................59  
6.7.6 Local Lockout (LLO)................................................................59  
6.7.7 Device Clear (DCL)...................................................................59  
6.7.8 Selected Device Clear (SDC) ....................................................59  
6.7.9 Serial Poll Disable (SPD) ..........................................................59  
6.7.10 Serial Poll Enable (SPE)..........................................................59  
6.7.11 Group Execute Trigger (GET)...............................................59  
6.7.12 Take Control (TCT)................................................................60  
6.7.13 Secondary Command Group (SCG) ......................................60  
6.7.14 Parallel Poll Configure (PPC).................................................60  
6.7.15 Parallel Poll Unconfigure (PPU)............................................60  
6.8 More on Service Requests.....................................................................60  
6.8.1 Serial Poll ...................................................................................61  
6.8.2 Parallel Poll................................................................................61  
7. Theory of Operation and Board Layout.......................................................62  
7.1 Theory of Operation.............................................................................62  
7.2 Board Layout .........................................................................................63  
Appendix A: Sample Dumb-Terminal Program...............................................65  
Appendix B: Character Codes and IEEE Multiline Messages .........................66  
Index...................................................................................................................68  
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RS-232IEEE 488 INTERFACE CONVERTER  
1. Specifications  
IEEE-488 Interface  
Implementation —  
C1, C2, C3, C4, and C28 controller subsets.  
Serial to IEEE: SH1, AH1, T6, TE0, L4, LE0,  
SR1, RL0, PP0, DC1, DT0, E1.  
Terminators —  
Selectable CR, LF, LF-CR, and CR-LF  
with EOI  
Connector —  
Standard IEEE 488 connector with metric studs  
Serial Interface  
EIA RS-232C —  
EIA RS-422A —  
Character Set —  
Output Voltage —  
AB, BA, BB, CA, CB  
Balanced voltage on TxD and RxD  
Asynchronous bit serial  
5 volts min. (RS-232C);  
5 volts typical (RS-422A)  
Input Voltage —  
Baud Rate —  
3 volts min.; q15v max.  
Selectable 110, 300, 600, 1200, 1800, 2400,  
3600, 4800, 7200, 9600, 19,200, and 57,600  
Data Format —  
Selectable 7 or 8 data bits; 1 or 2 stop bits;  
odd, even, mark, space, and no parity on  
transmit  
Duplex —  
Full with Echo/No Echo  
Serial Control —  
Terminators —  
Connector —  
Selectable CTS/RTS or XON/XOFF  
Selectable CR, LF, LF-CR, and CR-LF  
25-pin sub-D male, DCE configured  
10  
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CHAPTER 1: Specifications  
General  
Data Buffer —  
32,000 characters dynamically allocated  
Indicators —  
LEDs for IEEE Talk and Listen, Serial Send  
and Receive, and Power  
Power —  
105-125V or 210-250V; 50-60 Hz, 10 VA max.  
2.7"H x 5.5"W x 7.4"D (6.9 x 14 x 18.8 cm)  
3.6 lb. (1.6 kg)  
Size —  
Weight —  
Environment —  
0 to 50°C; 0 to 70% R.H. to 35°C.  
Linearly derate 3% R.H./degrees Centigrade  
from 35 to 50°C  
Controls —  
Power Switch (external), IEEE and Serial  
parameter switches (internal). Jumper  
selection of RS-232 or RS-422 operation  
(internal)  
Certification —  
FCC, CE  
WARNING!  
Do not use this interface outdoors. The interface is intended for indoor  
use only. Using this equipment outdoors could result in equipment  
failure, bodily injury, or death.  
CAUTION  
Do not connect AC line power directly to the RS-232IEEE 488 Interface  
Converter. Direct AC connection will damage equipment.  
11  
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RS-232IEEE 488 INTERFACE CONVERTER  
2. Introduction  
2.1 Description  
The RS-232488 Interface Converter provides transparent communication  
from a serial computer to an IEEE 488 printer, plotter, or other device. It also  
can be used to control a serial device, such as a printer or terminal, from an  
IEEE 488 host computer.  
As a serial-to-IEEE-488 converter, the interface converter receives data from  
a serial host then automatically performs the bus sequences necessary to send  
this data to the IEEE 488 device. If desired, data can be requested from the  
IEEE 488 device and returned to the host.  
As an IEEE 488 to serial converter the interface converter is a peripheral to  
an IEEE 488 controller. Data received from the controller is sent to the serial  
device, and the data received from the serial device is buffered for trans-  
mission to the IEEE 488 controller. The interface converter can inform  
the host, by the serial poll-status byte, that it has received data from the  
serial device.  
12  
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CHAPTER 2: Introduction  
2.2 Abbreviations  
The IEEE 488 abbreviations listed below are used throughout this manual.  
addr n  
ATN  
CA  
IEEE bus address “n”  
Attention line  
Controller Active  
Controller  
CO  
CR  
Carriage Return  
Data String  
Device Clear  
Group Execute Trigger  
Go To Local  
Listener Active  
Listen Address Group  
Line Feed  
data  
DCL  
GET  
GTL  
LA  
LAG  
LF  
LLO  
MLA  
MTA  
PE  
PPC  
PPU  
SC  
SDC  
SPD  
SPE  
SRQ  
TA  
TAD  
TCT  
term  
UNL  
UNT  
*
Local Lock Out  
My Listen Address  
My Talk Address  
Peripheral  
Parallel Poll Configure  
Parallel Poll Unconfigure  
System Controller  
Selected Device Clear  
Serial Poll Disable  
Serial Poll Enable  
Service Request  
Talker Active  
Talker Address  
Take Control  
Terminator  
Unlisten  
Untalk  
Unasserted  
13  
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RS-232IEEE 488 INTERFACE CONVERTER  
3. Getting Started  
3.1 Inspection  
The interface converter was carefully inspected, both mechanically and  
electrically, prior to shipment. When you receive it, carefully unpack all items  
from the shipping carton and check for any obvious signs of damage that may  
have occurred during shipment. Immediately report any damage found to the  
shipping agent. Remember to retain all shipping materials in the event that  
shipment back to the factory becomes necessary.  
Every interface converter is shipped with the following:  
• RS-232IEEE 488 Interface Converter  
• This instruction manual  
• Power supply  
3.2 Configuration  
Three DIP switches internal to the interface converter set the configuration  
of the interface.  
NOTE  
Selectable functions are read only at power-on and should only be set  
prior to applying power to the interface. The following figures illustrate  
the factory-default conditions, which are:  
Serial Port:  
IEEE:  
9600 Baud  
Mode = IEEE 488 Controller  
Address = 10  
Bus Terminator = LF; EOI Disabled  
Talk-Back on Terminator Enabled  
Talk-Back on Timeout Enabled  
8 Data Bits  
2 Stop Bits  
No Parity  
Serial Terminator = LF  
Echo Disabled  
RTS/CTS Handshake  
14  
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CHAPTER 3: Getting Started  
DOT  
1
2
3
4
5
6 7 8  
Switch  
Side  
View  
OPEN  
10  
LF  
Disabled  
IEEE Addr  
IEEE Term  
EOI  
DOT  
1
2
3
4
5
6 7 8  
Switch  
Side  
View  
OPEN  
C
Mode  
Talk-Back on Timeout  
Serial Term  
Enabled  
LF  
No Echo  
No Parity  
Echo  
Parity  
DOT  
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
9600  
RTS/CTS  
8 Data Bits  
Enabled  
2 Stop Bits  
Baud Rate  
Handshake  
Word Length  
Talk-Back on Term  
Stop Bits  
Figure 3-1. Factory-Default Settings.  
15  
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RS-232IEEE 488 INTERFACE CONVERTER  
Note that the interface converter comes configured as an IEEE controller. In  
this mode, the interface converter is designed to allow an RS-232 computer to  
communicate with an IEEE peripheral such as a plotter. This controller mode  
is described in detail in Chapter 4.  
The interface converter may also be configured as an IEEE peripheral. As an  
IEEE peripheral, it allows an IEEE controller to communicate with an RS-232  
device. The peripheral mode of operation is described in detail in Chapter 5.  
To modify any of these defaults, follow this simple procedure:  
1. Disconnect the power supply from the AC line and from the interface. Also  
disconnect any IEEE or serial cables.  
WARNING  
Never open the interface converter’s case while it is connected to the AC  
line. Failure to observe this warning may result in equipment failure,  
personal injury, or death.  
2. Place the interface converter upside down on a flat surface. Remove the  
four screws located near the rubber feet.  
3. Return the interface converter to the upright position and carefully remove  
the top cover.  
4. Change whichever DIP-switch settings you need to change.  
5. When you have made all your changes, reverse this procedure to  
reassemble the interface converter.  
3.3 Serial Port Settings  
The first parameters to configure are those that correspond to the RS-232  
port. These include baud rate, word length, number of stop bits, parity  
selection and type of RS-232 handshake. Each of these are described in  
the following sections.  
3.3.1 SERIAL BAUD RATE  
The “baud rate” is the number of serial data bits per second transferred into  
and out of the RS-232 interface. SW1-1 through SW1-4 determine the serial  
baud rate. The factory-default baud rate is 9600 baud. Baud rates may be  
selected from 110 to 57,600 baud. Refer to the following diagram for specific  
baud rates.  
16  
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CHAPTER 3: Getting Started  
DOT  
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
4
5
6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
4
5
6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
Switch  
Side  
View  
110  
110  
1800  
2400  
OPEN  
OPEN  
4
5
4
5
OPEN  
OPEN  
4
5
4
5
110  
3600  
OPEN  
OPEN  
4
5
4
5
135  
15 0  
300  
600  
1200  
4800  
OPEN  
OPEN  
4
5
4
5
7200  
OPEN  
OPEN  
4
5
4
5
9600  
OPEN  
OPEN  
4
5
4
5
19,200  
57,600  
OPEN  
OPEN  
4
5
4
5
OPEN  
OPEN  
Figure 3-2. Switch SW1: Selecting the Serial Baud Rate.  
17  
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RS-232IEEE 488 INTERFACE CONVERTER  
3.3.2 SERIAL WORD LENGTH (DATA BITS)  
SW1-6 determines the number of data bits, often referred to as word length,  
for each serial character transmitted or received. The factory default is 8 data  
bits.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
8 Data Bits  
7 Data Bits  
Figure 3-3. Switch SW1: Selecting the Serial Word Length (Data Bits).  
3.3.3 SERIAL STOP BITS  
Switch SW1-8 determines the number of stop bits contained in each serial  
character transmitted and received. The factory default is 2 stop bits.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
1 Stop Bit  
2 Stop Bits  
Figure 3-4. Switch SW1: Selecting the Serial Stop Bits.  
18  
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CHAPTER 3: Getting Started  
3.3.4 SERIAL PARITY  
Serial Parity is selected with S2-6 through S2-8. The interface converter  
generates the selected parity during serial transmissions but it does not  
check parity on data that is received. The factory default is parity disabled.  
DOT  
1
1
2
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
Odd Parity  
Mark Parity  
3
4
5
6
7
8
1
2
3
4
5
6
7
8
OPEN  
OPEN  
Even Parity  
Space Parity  
1
2
3
4
5
6
7
8
OPEN  
Parity Disabled  
Figure 3-5. Switch SW2: Selecting the Serial Parity.  
3.3.5 SERIAL ECHO  
Serial data sent to the interface converter will be echoed back to the serial  
host if SW2-5 is set to the open position. The factory default is Echo Disabled.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
Echo Disabled  
Echo Enabled  
Figure 3-6. Switch SW2: Enabling or Disabling Echo.  
19  
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RS-232IEEE 488 INTERFACE CONVERTER  
3.3.6 SERIAL HANDSHAKE  
Switch SW1-5 is used to select hardware [RTS/CTS] or software [Xon/Xoff]  
serial handshake control.  
With X-ON/X-OFF, the interface converter issues an X-OFF character [ASCII  
value of $13] when its buffer memory is near full. When the X-OFF character  
is sent, there are still more than 1000 character locations remaining to protect  
against buffer overrun. When it is able to accept more information, the inter-  
face converter issues an Xon character [ASCII value of $11]. The interface  
converter also accepts X-ON/X-OFF on transmit from the serial host it is  
communicating with. RTS/CTS serial control becomes inactive when X-  
ON/X-OFF is enabled. The RTS output is, however, set to an active high  
state. The CTS input is not used for this handshake and may be left  
floating (unconnected).  
With RTS/CTS, the interface converter un-asserts RTS (sets RTS low) when  
its buffer memory is near full. When RTS is un-asserted, there are still more  
than 1000 character locations remaining to protect against buffer overrun.  
When it is able to accept more information, the interface converter asserts  
RTS (sets RTS high). The interface converter will not transmit data to the  
serial host if it detects the CTS input un-asserted (low) when configured  
for this hardware handshake.  
The factory-default serial control is hardware, RTS/CTS.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
RTS/CTS  
X-ON/X-OFF  
Figure 3-7. Switch SW1: Selecting the Serial Handshake.  
20  
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CHAPTER 3: Getting Started  
3.4 Selecting Terminator Substitution  
The interface converter can be configured to provide RS-232-to-IEEE-488 and  
IEEE-488-to-RS-232 terminator substitution. This is useful when interfacing an  
RS-232 device which only issues carriage return [CR] as an output terminator  
to an IEEE controller which expects a carriage return followed by a line feed  
[CR-LF].  
In a case like that, the serial terminator should be selected for CR Only while  
the IEEE terminator is set to CR-LF. When a serial CR character is received,  
it is discarded, and an IEEE CR-LF is substituted for it. In the IEEE-to-RS-232  
direction, the IEEE CR is unconditionally discarded. Upon receipt of the  
IEEE LF, a serial CR is substituted.  
The interface converter can be made totally data transparent by setting both  
the serial and IEEE terminators to be CR Only or LF Only.  
3.4.1 SERIAL TERMINATOR  
SW2-3 and SW2-4 select the serial terminators for the serial input and output.  
The factory default is LF Only.  
DOT  
1
1
2
2
3
4
5
6
7
7
8
8
1
1
2
2
3
3
4
5
6
6
7
7
8
8
Switch  
Side  
View  
OPEN  
OPEN  
CR Only  
LF-CR  
3
4
5
6
4
5
OPEN  
OPEN  
LF Only  
CR-LF  
Figure 3-8. Switch SW2: Selecting the Serial Terminator.  
21  
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RS-232IEEE 488 INTERFACE CONVERTER  
3.4.2 IEEE BUS TERMINATOR  
SW3-6 through SW3-8 set the IEEE bus terminators used for data sent or  
received by the interface converter. EOI, a line used to signal the end of  
a multiple character bus transfer, may also be enabled. If enabled, EOI  
is asserted when the last selected bus terminator is sent. Factory default  
is LF Only with EOI disabled.  
DOT  
1
1
1
2
2
2
3
4
5
6
7
7
7
8
8
8
1
1
1
2
2
2
3
3
3
4
5
6
7
7
7
8
8
8
Switch  
Side  
View  
OPEN  
OPEN  
CR Only  
LF-CR  
3
4
5
6
4
5
6
OPEN  
OPEN  
LF Only  
CR-LF  
3
4
5
6
4
5
6
OPEN  
OPEN  
EOI Disabled  
EOI Enabled  
Figure 3-9. Switch SW3: Selecting the IEEE Bus Terminator.  
3.5 Selecting the Mode  
SW2-1 sets the major operating mode of the interface converter. The IEEE  
Controller (RS-232-to-IEEE converter) mode allows a serial host device to  
send data to a single IEEE bus peripheral. Applications include interfacing  
a listen-only or addressable IEEE printer/plotter to a serial printer port.  
Refer to Chapter 4 for more detailed information on the controller mode  
of operation.  
The Peripheral mode is used when interfacing a serial device to an IEEE  
controller. Data which is sent by the IEEE controller to the interface  
converter is transmitted out its serial port. Data received from the serial  
device is buffered by the interface converter until read by the IEEE controller.  
Refer to Chapter 5 for more detailed information on the peripheral mode  
of operation.  
The factory default is the IEEE Controller mode, an RS-232-to-IEEE  
converter.  
22  
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CHAPTER 3: Getting Started  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
Controller Mode  
Peripheral Mode  
Figure 3-10. Switch SW2: Selecting the Mode.  
3.6 Selecting the IEEE Address  
SW3-1 through SW3-5 select the IEEE bus address of the interface converter  
when in the IEEE Peripheral mode. These same switches are used in the IEEE  
Controller mode to select the address of the device that will be controlled.  
[Refer to Chapters 5 and 4 respectively for additional information]. The  
address is selected by simple binary weighting, with SW3-1 being the least  
significant bit and SW3-5 the most significant. The factory default is address 10.  
Listen Only is a special type of Peripheral operation. In the Listen Only mode  
the interface converter accepts all data transmitted on the bus, ignoring any  
bus addressing, and transfers it out its serial port. The interface converter is  
set to Listen Only mode by setting its address to 31. If the IEEE address is set  
to 31 in the peripheral mode, it is adjusted to 30.  
DOT  
1
2
3
4
5
6
7
8
0
1
Switch  
Side  
View  
OPEN  
0 x 16 -0  
1 x 8  
0 x 4  
1 x 2  
-8  
-0  
-2  
0 x 1 + -0  
IEEE Address = 10  
Figure 3-11. Switch SW3: Selecting the IEEE Address.  
23  
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RS-232IEEE 488 INTERFACE CONVERTER  
3.7 Feature Selections  
The functions of the remaining switches are dependent on the mode  
selected. A brief description of each of these features follows. You should  
refer to the listed sections for additional information.  
3.7.1 CONTROLLER FEATURES  
In the IEEE Controller (RS-232-to-IEEE 488 Converter) mode, SW1-7 is  
used to determine whether the interface should, after sending the IEEE  
bus terminators, address the attached bus device to talk. The factory default  
is Talk-Back On Terminator enabled.  
SW2-2 selects whether the interface converter should address the attached bus  
device to talk when the interface converter has nothing more to send to that  
device. The factory default is Talk-Back On Timeout enabled.  
Refer to Chapter 4 for complete details on these features.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
Talk-Back on  
Terminator Disabled  
Talk-Back on  
Terminator Enabled  
Figure 3-12. Switch SW1: Enabling or Disabling “Talk Back  
on Terminator” in Controller Mode.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
Talk-Back on  
Timeout Disabled  
Talk-Back on  
Timeout Enabled  
Figure 3-13. Switch SW2: Enabling or Disabling “Talk Back  
on Timeout” in Controller Mode.  
24  
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CHAPTER 3: Getting Started  
3.7.2 PERIPHERAL FEATURES  
In the IEEE Peripheral (IEEE 488 to RS-232 converter) mode, SW1-7 enables  
the interface to assert the SRQ IEEE bus interface line to indicate that it has  
received the last switch selected serial terminator character from the serial  
device.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
SRQ on Last  
Terminator Disabled  
SRQ on Last  
Terminator Enabled  
Figure 3-14. Switch SW1: Enabling or Disabling SRQ on Last Serial  
Terminator in Peripheral Mode.  
3.8 Serial Interface  
The interface converter has the ability to output signal levels that are  
compatible with either RS-232 or RS-422. An internal DIP shorting plug  
determines which electrical specification is chosen. If the interface is to be  
®
connected to an IBM PC or compatible, the RS-232 level should be selected.  
®
If it will be connected to a Macintosh , the RS-422 level should be used. For  
connection to other computers, refer to the manufacturer’s manual to  
determine which levels are supported.  
25  
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RS-232IEEE 488 INTERFACE CONVERTER  
3.8.1 RS-232/RS-422 SIGNAL LEVEL SELECTION  
The interface converter’s factory default signal levels are compatible with  
RS-232. To select RS-422 levels, carefully remove the 8-position shorting plug  
with a small flat blade screwdriver from J106. Install the DIP jumper into J205  
making certain that all of the pins on the shorting plug are inserted correctly.  
Shorting Plug  
RS-422  
RS-232  
Figure 3-15. Selecting RS-232 or RS-422 Signal Levels.  
3.8.2 SERIAL SIGNAL DESCRIPTIONS  
The interface converter is equipped with a standard DB25 female connector  
on its rear panel and requires a standard DB25 male mating connector. The  
interface converter’s connector is configured as DCE type equipment for  
RS-232 communications, which means the interface converter always trans-  
mits data on Pin 3 and receives the data on Pin 2. The following lists and  
describes the RS-232 and RS-422 signals provided on the interface converter.  
26  
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CHAPTER 3: Getting Started  
13  
25  
1
14  
Figure 3-16. Rear View of the Interface Converter’s Serial Connector.  
-RxD  
Receive Data—Input—Pin 2  
This pin accepts serial data sent by the RS-232 or RS-422 host. The serial  
data is expected with the word length, baud rate, stop bits, and parity  
selected by the internal switches. The signal level is low true.  
-TxD  
Transmit Data—Output—Pin 3  
This pin transmits serial data to the RS-232 or RS-422 host. The serial data  
is sent with the word length, baud rate, stop bits, and parity selected by the  
internal switches. The signal level is low true.  
CTS  
Clear To Send—Input—Pin 4  
The CTS input is used as a hardware-handshake line to prevent the  
interface converter from transmitting serial data when the RS-232 host  
is not ready to accept it. When RTS/CTS handshake is selected on the  
internal switches, the interface converter will not transmit data out -TxD  
while this line is un-asserted (lowered). If the RS-232 host is not capable  
of driving this line it can be connected to the Vtest output (Pin 6) of the  
interface converter. If X-ON/X-OFF handshake is selected, the CTS line  
is not tested to determine if it can transmit data.  
RTS  
Request To Send—Output—Pin 5  
The RTS output is used as a hardware handshake line to prevent the  
RS-232/RS-422 host from transmitting serial data if the interface converter  
is not ready to accept it. When RTS/CTS handshake is selected on the  
internal switches, the interface converter will drive the RTS output high  
when there are more than 1,000 character locations available in its  
internal buffer. If the number of available locations drops to less than  
1,000, the interface converter will unassert (lower) this output. If  
Xon/Xoff handshake is selected, the RTS line will be permanently  
driven active (high).  
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RS-232IEEE 488 INTERFACE CONVERTER  
Vtest  
Test Voltage—Output—Pin 6  
This pin is connected to +5 volts through a 1K resistor. It is also common  
to Vtest on Pin 9.  
Gnd  
Ground—Pin 7  
This pin sets the ground reference point for the other RS-232 inputs and  
outputs.  
Vtest  
Test Voltage—Output—Pin 9  
This pin is connected to +5 volts through a 1K resistor. It is also common  
to Vtest on Pin 6.  
+RxD  
Receive Data Plus—Input—Pin 14  
This pin accepts serial data sent by the RS-422 host. The serial data is  
expected with the word length, baud rate, stop bits, and parity selected by  
the internal switches. The signal level is high true and only connected to  
this pin when RS-422 operation is selected. It is 180 degrees out of phase  
with -RxD.  
+TxD  
Transmit Data Plus—Output—Pin 16  
This pin transmits serial data to the RS-422 host. The serial data is sent  
with the word length, baud rate, stop bits, and parity selected by the  
internal switches. The signal level is high true and only connected to  
this pin when RS-422 operation is selected. It is 180 degrees out of phase  
with -TxD.  
28  
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CHAPTER 3: Getting Started  
3.8.3 SERIAL-CABLE WIRING DIAGRAMS  
If a cable was not purchased with the interface, the following diagrams will be  
helpful in making your own cable. Simple soldering skills and an attention to  
detail will ensure successful construction.  
Mini DINs Male  
DB25 Male  
RTS 1  
CTS 2  
-TxD 3  
Gnd 4  
-RxD 5  
+TxD 6  
+RxD 8  
4 CTS  
5 RTS  
2 -RxD  
7 Gnd  
3 -TxD  
14 +RxD  
16 +TxD  
Figure 3-17. Wiring Diagram:  
Macintosh to Interface Converter (RS-422).  
DB25 Female  
DB25 Male  
-TxD 2  
-RxD 3  
RTS 4  
CTS 5  
DSR 6  
Gnd 7  
2 -RxD  
3 -TxD  
4 CTS  
5 RTS  
3 V test  
7 Gnd  
Figure 3-18. Wiring Diagram: IBM PC or Compatible with  
DB25 Serial Connector to Interface Converter (RS-232).  
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RS-232IEEE 488 INTERFACE CONVERTER  
DB9 Female  
DB25 Male  
DCD 1  
-RxD 2  
-TxD 3  
DTR 4  
Gnd 5  
DSR 6  
RTS 7  
3 -TxD  
2 -RxD  
7 Gnd  
4 CTS  
5 RTS  
CTS 8  
Figure 3-19. Wiring Diagram: IBM AT or Compatible with DB9 Serial  
Connector to Interface Converter (RS-232).  
NOTE  
Standard AT 9-pin-to-25-pin adapter cables are not wired as shown  
above and will not work with the interface converter.  
3.9 General  
Refer to the following sections for specific operational modes. This sub-  
section gives a general test of functionality. After setting the power-on defaults  
and reassembling the interface converter, plug the power-supply connector  
into the rear jack on the interface.  
CAUTION  
Never plug the power supply into the interface while it is connected to  
AC line power. If you do, you could damage the interface converter.  
WARNING  
The power supply provided with the interface converter is intended for  
INDOOR USE ONLY. Using it outdoors could result in equipment failure,  
personal injury, or death.  
30  
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CHAPTER 3: Getting Started  
After plugging the power-supply connector into the interface, plug the power  
supply into AC line power. Turn the rear-panel power switch ON (the “1”  
position). All the front-panel indicators should light momentarily while the  
interface converter performs an internal ROM and RAM self-check. At the  
end of this self-check, all indicators except POWER should turn off.  
If there is an error in the ROM checksum, all of the LEDs will remain on.  
Flashing LEDs indicate a RAM failure. Should such an error occur, turn the  
rear-panel switch to the OFF [0] position and retry the above procedure.  
If the front-panel indicators do not flash and the POWER indicator does not  
remain lit, there may not be any power supplied to the interface. In this event,  
check the AC line and the rear-panel connection of the power supply. If the  
problem is unresolved, call your supplier.  
If proper operation is obtained, connect an interface cable to the DB25 port  
on the rear of the interface converter. Connect the other end to the host’s  
serial port. Except for connecting IEEE bus instruments, the interface  
converter is installed and ready to use.  
WARNING  
The interface converter makes its earth-ground connection through the  
serial interface cable. It should only be connected to the IEEE host.  
Failure to do so may allow the interface converter to float to a bus-device  
test voltage. This could result in damage to the interface, personal injury,  
or death.  
31  
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RS-232IEEE 488 INTERFACE CONVERTER  
4. Controller Operation  
4.1 Controller-Mode (Serial to IEEE) Operation  
The IEEE Controller mode allows a serial RS-232 or RS-422 host device to  
send data to a single IEEE bus peripheral or to multiple peripherals if they  
occupy the same bus address. Applications include interfacing a listen-only  
or addressable IEEE printer/plotter to a serial printer port.  
Once the interface converter has initialized itself after power-on, it waits for  
serial input data. When received, it addresses the selected IEEE device to  
listen with the following bus sequence:  
ATNUNL,MTA,LAG,*ATN  
The data received from the serial host is placed into a circular serial input  
buffer. Simultaneously, characters are removed from that buffer and sent  
to the IEEE bus device. The serial terminator(s), if present, are not sent.  
Instead, the IEEE terminators are substituted and sent in their place.  
As long as the serial input buffer is not empty, the interface converter will  
continue to send data from it to the IEEE bus device. If the serial input buffer  
becomes emptied, the interface converter will command the IEEE bus device  
to talk if one of the talk-back features is enabled. This allows the interface  
converter to be used as a controller with devices, such as plotters or  
instruments, that return status and other information to the host computer.  
When the interface converter addresses the IEEE bus device to talk it uses the  
following bus sequence:  
ATNUNL,MLA,TAG,*ATN  
The interface converter then accepts data from the IEEE device and returns  
it to the host until the last selected IEEE terminator is detected. The IEEE bus  
terminators are replaced by the serial terminators, and these are then sent to  
the serial host.  
If the IEEE device has been addressed to talk but does not respond or finish  
transmission by the time additional characters are received in the circular  
serial-input buffer, the talk sequence will be aborted to allow additional  
serial information to be sent to the IEEE device.  
32  
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CHAPTER 4: Controller Operation  
4.2 Serial and IEEE Terminator Substitution  
The interface converter can be configured to provide serial-to-IEEE-488 and  
IEEE-488-to-serial terminator substitution. This is useful when interfacing a  
serial host which only issues carriage return [CR] as an output terminator to  
an IEEE peripheral which expects a carriage return followed by a line feed  
[CR-LF].  
In this case, the serial terminator should be selected for CR Only while the  
IEEE terminator is set for CR-LF. When a serial CR character is received, it is  
discarded and replaced with an IEEE CR followed by an IEEE LF. In the IEEE  
to serial direction, the IEEE CR is unconditionally discarded. Upon receipt of  
the IEEE LF a serial CR is substituted.  
The interface converter can be made totally data-transparent by setting both  
the serial and IEEE terminators to be CR Only or LF Only. Refer to Chapter 3  
for the proper switch settings for both the IEEE and serial terminators.  
33  
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RS-232IEEE 488 INTERFACE CONVERTER  
4.3 IEEE Address Selection  
SW3-1 through SW3-5 select the IEEE bus address of the IEEE peripheral  
the interface converter will be communicating with. These switches set the  
address of the IEEE device that will be controlled, not the address of the  
interface converter. The address of the interface converter is automatically  
adjusted so that address conflicts will not occur. The address is selected by  
simple binary weighting with SW3-1 being the least significant bit and SW3-5  
the most significant. If address 31 (reserved on the IEEE bus) is selected  
in the controller mode, address 30 is assigned as the device it will be  
communicating with. The following figure shows the IEEE address  
selection of 10.  
DOT  
1
2
3
4
5
6
7
8
0
1
Switch  
Side  
View  
OPEN  
0 x 16 -0  
1 x 8  
0 x 4  
1 x 2  
-8  
-0  
-2  
0 x 1 + -0  
IEEE Address = 10  
Figure 4-1. Switch SW3: Selecting the IEEE Address.  
4.4 Talk-Back Features  
Two different switch-selectable talk-back features are included to provide bi-  
directional communication with the IEEE device. Whether either talk-back  
feature should be enabled depends on the application.  
4.4.1 TALK-BACK ON TERMINATOR  
SW1-7 is used to determine whether the interface should address the attached  
bus device to talk after sending the selected IEEE bus terminator(s). This  
feature is commonly used to provide bidirectional communication with a  
single IEEE instrument. Talk-back will only occur if there is no serial data to  
output to the IEEE device. The factory default is Talk-Back On Terminator  
enabled.  
34  
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CHAPTER 4: Controller Operation  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
Talk-Back on  
Terminator Disabled  
Talk-Back on  
Terminator Enabled  
Figure 4-2. Switch SW1: Enabling or Disabling  
“Talk-Back on Terminator.”  
When the serial input buffer becomes empty, the interface converter checks  
the last characters sent to the IEEE bus device. If these were the IEEE bus  
terminators and Talk-Back on Terminator is enabled, the IEEE bus device is  
addressed to talk. Any data received by the interface converter from the bus  
device is sent to the serial host.  
When the last IEEE bus terminator is detected from the IEEE device, the  
interface converter disables the device from sending additional information  
by asserting Attention (ATN) on the bus.  
If the IEEE device does not responded or finish transmission by the time  
additional characters are received into the serial input buffer, the talk  
sequence will be aborted to allow additional serial information to be sent to  
the IEEE device.  
The program example on the next page shows how this feature can be used to  
communicate with a single IEEE instrument. The program example is written  
in BASIC on an IBM PC or compatible and communicates with a Keithley  
Model 196 DMM.  
10  
'
'
'
'
'
'
20  
Example Program using interface converter with  
the Talk-Back on Terminator feature enabled to  
communicate with a Keithley Model 196 DMM  
25  
30  
40  
50  
Open BASIC’s serial communications port  
OPEN "COM1: 9600, N, 8, 2" AS 1  
60  
70  
'
Set the Model 196 DMM to the 30VDC range  
PRINT #1, "F0R3X"; ' The ; suppresses terminators  
Request 10 Readings from 196”  
FOR N=1 to 10  
PRINT #1," " ' Output terminator  
80  
90  
'
100  
110  
120  
130  
140  
150  
LINE INPUT #1, A$ ' Get reading from 196  
PRINT A$ ' print it on the screen  
NEXT N  
END  
35  
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RS-232IEEE 488 INTERFACE CONVERTER  
4.4.2 TALK-BACK ON TIMEOUT  
SW2-2 selects whether the interface converter should address the attached  
bus device to talk when the interface converter has no more serial data to  
send. This feature relies on time and not on terminators. Its use is primarily  
for simulating a serial plotter from an IEEE 488 (HP-IB) plotter. The factory  
default is Talk-Back On Timeout enabled.  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
Talk-Back on  
Timeout Disabled  
Talk-Back on  
Timeout Enabled  
Figure 4-3. Switch SW2: Enabling or Disabling  
Talk-Back on Timeout.”  
If Talk-Back on Timeout is enabled, the interface converter waits  
approximately 100 milliseconds after it detects that its serial input buffer is  
empty. If no serial character has been received by the end of this time, the  
IEEE bus device is addressed to talk. The choice of talk-back modes depends  
strongly on the type of device and software being used. For most plotter  
applications, the Talk-Back on Timeout feature should be enabled.  
When the last IEEE bus terminator is detected from the IEEE device, the  
interface converter disables the device from sending additional information  
by asserting Attention (ATN) on the bus. If the IEEE device does not respond  
or finish transmission by the time additional characters are received into the  
serial input buffer, the talk sequence will be aborted to allow additional serial  
information to be sent to the IEEE device.  
Most IEEE 488 plotters will not respond to the talk address sequence with  
output data unless there has been a specific device dependent command  
sent to tell them what to say. If they have not been told what to say, they  
say nothing.  
36  
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CHAPTER 4: Controller Operation  
The following is an example of how this feature can be used to communicate  
with an IEEE plotter. The program example is written in BASIC on an IBM  
PC or compatible. It turns the PC into a dumb serial terminal. When a key  
is pressed on the keyboard, the character is transmitted out of the serial  
(COM1) port. Any serial data which is received from the port is printed  
on the display.  
10 ' Dumb Terminal Program for the interface converter  
20 ' This program allows direct interaction between  
30 ' the IBM PC and an IEEE plotter through the  
40 ' interface converter. The interface converter must have Talk-Back  
50 '  
on Timeout enabled.  
60 'Open the serial communications port  
70 OPEN "COM1: 9600,n,8,2,cs,ds" AS 1  
80 ' Display any data received from the COM1 port  
90 IF LOC(1) THEN PRINT INPUT$(LOC(1),1);: GOTO 90  
100 ' Transmit key presses to the COM1 port and screen  
110 K$=INKEY$  
120 PRINT #1, K$; : PRINT K$;  
130 GOTO 90 ' Do it again  
Enter the program into the computer and run it. The example below shows  
®
how to test the interface converter’s operation with a Hewlett-Packard 7470A  
plotter. Other IEEE plotters are similar, but you should refer to the plotter’s  
programming manual for the proper command syntax. Notice the interface  
converter’s front-panel LEDs as you type the plotter commands.  
®
Type the following HP-GL output-identify command on the keyboard...  
OI;  
®
The plotter (HP 7470A) should immediately respond with.....  
7470A  
When you type the following HP-GL command on the keyboard, the plotter  
should respond by retrieving its pen, drawing a line and returning the pen.  
SP1;PA1000,1000;PD;PA1000,6000;PU;SP0;  
37  
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RS-232IEEE 488 INTERFACE CONVERTER  
4.5 Plotter Applications  
To use the interface converter to interface an HP-IB plotter to a serial  
computer port, you will need the following information about your system:  
1) The serial data format that the application (plotting or graphics)  
program expects the plotter to communicate with. These parameters  
include baud rate, word length, stop bits, parity and serial control.  
Some programs allow these parameters to be selected by the user. Other  
graphics programs depend on the RS-232 version of the plotter defaults.  
Usually, Hewlett-Packard plotters use 9600 baud, 7 data bits, 1 stop bit,  
even parity, and X-ON/X-OFF serial control. Since these plotters are  
available with serial interfaces, the operator’s manual of your IEEE  
plotter should contain this information.  
2) The IEEE bus address of your plotter. This address is usually set by a DIP  
switch located on the rear of the plotter. The first five switches set the  
address, which, for Hewlett-Packard plotters, is usually address 5. Refer  
to the plotter’s operator’s manual for exact information.  
Set the interface converter’s internal DIP switches to match the parameters  
determined above. Other parameters which should be selected include:  
1. Talk-Back on Terminator Enabled.  
2. Talk-Back on Timeout Enabled.  
3. Serial Terminators set to CR Only.  
4. IEEE Terminators set to CR Only with EOI enabled.  
38  
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CHAPTER 4: Controller Operation  
RS-232  
IEEE 488  
Interface  
Converter  
Figure 4-4. A PC-Based Graphics System.  
The following shows the interface converter’s internal switch settings required  
®
to use a Hewlett-Packard 7580A plotter with AutoCAD from AUTODESK on  
an IBM PC or compatible. Because PCs and compatibles output RS-232 levels,  
the shorting DIP jumper should be set to the RS-232 position (J206).  
Shorting Plug  
RS-232  
RS-422  
Figure 4-5. Selecting RS-232 Signal Levels.  
39  
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RS-232IEEE 488 INTERFACE CONVERTER  
DOT  
1
2
3
4
5
6 7 8  
Switch  
Side  
View  
OPEN  
5
IEEE Addr  
IEEE Term  
EOI  
CR Only  
Enabled  
DOT  
1
2
3
4
5
6 7 8  
Switch  
Side  
View  
OPEN  
C
Mode  
Talk-Back on Timeout  
Serial Term  
Enabled  
CR  
No Echo  
Even  
Echo  
Parity  
DOT  
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
9600  
Baud Rate  
Handshake  
Word Length  
X-ON/X-OFF  
7 Data Bits  
Enabled  
Talk-Back on Terminator  
Stop Bits  
1 Stop Bit  
Figure 4-6. Interface Converter Settings for Use with HP 7580A Plotter  
on an IBM PC.  
When using the interface converter with plotting programs on the Macintosh  
®
computer with graphic drivers such as MacPlot , some serial data format  
parameters are user-modifiable. The following is a partial MacPlot config-  
uration screen which allows selection of baud rate, stop bits, and parity. With  
this driver, the word length is fixed to 7 data bits with X-ON/X-OFF serial  
control. These non-modifiable defaults are plotter dependent. Refer  
to the plotter or driver manual for the defaults of the specific plotter.  
For this example, 57600 baud with one stop bit and no parity has been  
chosen for the serial data format.  
40  
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CHAPTER 4: Controller Operation  
File  
Edit  
Windows  
Stop Bits:  
Settings for HP 7500A  
Baud Rate:  
Parity:  
Paper Si  
1
57600  
None  
Apple Plotter  
Graphic MP31 / 2 / 300  
H.P. 7220  
Houst  
Houst  
Houst  
Houst  
Houst  
Houst  
Houst  
Houst  
Houst  
Calcomp 104x/7x,9x5  
Calcomp 81  
H.P. 7440A ColorPro  
H.P. 7470A  
Colorwriter 6200DS10  
Colorwriter 6310  
Colorwriter 6320  
Epson HI-80  
H.P. 7475  
H.P. 7550A  
H.P. 7570A DraftPro  
H.P. 7580B  
Facit 4551  
H.P. 7585B  
Graphtec FP5301  
Figure 4-7. MacPlot Configuration Screen.  
IEEE 488  
RS-422  
Interface  
Converter  
Figure 4-8. A Macintosh Based Graphics System.  
The Macintosh computer outputs RS-422 levels. Because of this, the internal  
DIP shorting jumper is set to the RS-422 position (J205).  
41  
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RS-232IEEE 488 INTERFACE CONVERTER  
Shorting Plug  
RS-232  
RS-422  
Figure 4-9. Setting the Internal DIP Shorting Jumper for RS-422.  
The following illustrates the interface converter’s internal switch settings  
for use with MacPlot, using the previously described format.  
42  
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CHAPTER 4: Controller Operation  
DOT  
1
2
3
4
5
6 7 8  
Switch  
Side  
View  
OPEN  
5
CR  
Enabled  
IEEE Addr  
IEEE Term  
EOI  
DOT  
1
2
3
4
5
6 7 8  
Switch  
Side  
View  
OPEN  
C
Mode  
Talk-Back on Timeout  
Serial Term  
Enabled  
CR  
No Echo  
No Parity  
Echo  
Parity  
DOT  
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
57600  
Baud Rate  
Handshake  
Word Length  
X-ON/X-OFF  
7 Data Bits  
Enabled  
Talk-Back on Terminator  
Stop Bits  
1 Stop Bit  
Figure 4-10. Interface Converter Settings for Use with HP 7580A  
Plotter on a Macintosh.  
After configuration, turn on the plotter and the interface converter. The  
interface converter’s front-panel LEDs should all light momentarily while it  
performs an internal ROM and RAM test. All LEDs should go out except for  
the Power and Talk LED. The Talk LED indicates that the interface converter  
has detected the plotter on the IEEE bus and has addressed it to listen.  
When the serial host begins to send the interface converter data, the Receive  
LED will flash. If it does not, this indicates that the interface is not receiving  
data from the serial host. Verify the cables are connected properly and the  
serial cable wiring. Verify the serial data format, word length, stop bits and  
parity.  
43  
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RS-232IEEE 488 INTERFACE CONVERTER  
4.6 Printer Applications  
Most of the information given for plotter applications applies to applications  
for interfacing IEEE 488 printers to a serial host. Some high-end printers have  
a secondary command setting which must be disabled for the interface  
converter to control them. The interface converter does not use secondary  
commands to control IEEE peripherals, such as printers or plotters. Refer to  
the printer’s instruction manual if there is a question as to whether the  
printer requires secondary commands.  
44  
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CHAPTER 5: Peripheral Operation  
5. Peripheral Operation  
5.1 Peripheral-Mode Operation  
This mode of operation is useful in interfacing a serial device, such as a serial  
printer, plotter or instrument, to an IEEE controller. Data which is sent by the  
IEEE controller to the interface converter is buffered and transmitted out its  
serial port. Data received from the serial device is buffered by the interface  
converter until read by the IEEE controller. The interface converter can  
buffer approximately 32,000 bytes of data from both the IEEE input and the  
serial input.  
The interface converter will refuse to accept more data from the IEEE  
controller when its buffer memory is full. It does this by preventing  
completion of the bus handshaking sequences. It will also request that  
additional serial data not be sent by negating its Request To Send (RTS)  
output or by transmitting the X-OFF ASCII character. The serial handshake  
used depends on the handshake selection (see Chapter 3).  
5.2 Serial and IEEE Input Buffers  
Memory in the interface converter is dynamically allocated for the serial input  
and IEEE input buffers. This allows for the most efficient partitioning of  
memory for any given application.  
At power on, or device clear, each buffer is allocated a 128-byte mini-buffer  
or queue. When the serial input (or IEEE input) requires more buffer space,  
additional queues are allocated. When a queue is empty, it is released from  
the input buffers so that it may be re-allocated wherever it is required.  
There are approximately 250 available queues for a total of 32,000 bytes of  
buffer (character) space. Queues are continually allocated and released as  
required by the serial and IEEE input. Of the 250 available queues, 240 are  
issued without regard to controlling the receipt of additional serial or IEEE  
input data.  
When the serial input buffer requests one of the last 10 queues (in other  
words, when there are 1280 character locations left), it signals the serial host  
that it should stop sending data. This is accomplished by either unasserting  
RTS or issuing “X-OFF,” depending on which serial handshake control has  
been switch selected.  
45  
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RS-232IEEE 488 INTERFACE CONVERTER  
When more than 10 queues become available, it asserts RTS or issues “X-ON.”  
The IEEE bus input signals that the IEEE input (or serial output) buffer is full  
when the number of queues available drops below 10 (1280 character  
locations left). When the number of available queues drops to 4 or less (512  
character locations left), the IEEE interface of the interface converter stops  
accepting data from the bus. This bus hold-off will only occur until additional  
queues (more than 4) become available. Then the interface will resume  
accepting bus data.  
5.3 IEEE Data Transfers  
The following methods may be used by the IEEE controller when sending  
data to the interface converter:  
5.3.1 BLIND BUS DATA TRANSFERS  
If the IEEE controller does not mind waiting an indefinite time for data space  
in the buffer to become available, the data can simply be sent to the interface  
converter. This is referred to as “blind data transfer,” because the IEEE  
controller is blind as to whether or not the interface converter is capable  
of accepting data. In this case, the bus controller’s output data transfer will  
be held off by the interface converter if it is unable to buffer the data. It will  
resume accepting IEEE input data when memory becomes available. This  
type of control might be appropriate in a single-user environment.  
To illustrate how this would appear, let’s assume the interface converter is  
connected to a serial device which will accept data at 1200 baud or 110 bytes  
per second. The IEEE bus controller is capable of sending data to the  
interface converter at a rate of 5000 bytes per second. The data would be  
transferred on the bus at 5000 characters per second for slightly over six  
seconds, filling over 31,000 locations. At that time, the IEEE input would  
hold off additional data transfers until 128 characters are sent out the serial  
port at rate of 110 characters per second. This 110 cps would then become  
the average bus data acceptance rate of the interface converter.  
If the controller is set to detect a data time-out error, then it will do so if the  
interface converter holds off IEEE input data transfers for too long. The error  
can be used to alert the operator to the problem, such as a printer out of  
paper, so that it can be corrected. If the controller then restarts transmission  
exactly where it left off, no data will be lost.  
If data is requested by the controller and no serial input data is available in  
the interface converter, the bus will hang until serial data is received. If no  
serial data is received, it will hang forever until the controller times out.  
46  
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CHAPTER 5: Peripheral Operation  
5.3.2 CONTROLLED BUS DATA TRANSFERS  
If the controller must avoid waiting for the serial device, it can “serial-poll” the  
interface converter. Serial polling is a method by which the controller can  
inquire the internal status of the interface without disturbing any data being  
transferred, slowing data transfers, or locking up the bus. You should refer to  
the programming manual of your controller to determine the method of  
performing serial polls.  
When serial-polled, the interface converter provides eight bits of status  
information to the controller. The most significant bit (DIO8) of the  
interface converter’s serial poll byte is set to a logic “1” when the IEEE input  
buffer is NOT EMPTY. The term NOT EMPTY is used to signify that not all  
of the previous data sent to the interface has been transmitted to the serial  
device. If it is NOT EMPTY, the controller may avoid sending any more data  
to the interface converter. If this bit is a logic “0,” then the serial device has  
accepted all previous data and the IEEE controller may send more.  
Another bit (DIO4) of the Serial Poll byte is used to indicate additional  
information concerning the IEEE input buffer. This bit is set to a logic “1”  
when there is 1280 or less locations in the buffer for data. It is cleared, set  
to a logic “0”, when there is greater than 1280 locations available. This bit is  
referred to as the IEEE input buffer FULL bit.  
When serial data is received, DIO5 of the Serial Poll byte is set to “1”, to  
indicate to the IEEE controller that the serial input buffer is NOT EMPTY. If  
this bit is set, it indicates that at least one character is available in the serial  
input buffer to be read by the IEEE controller. Once all of the serial input  
data is read by the IEEE controller this bit is reset.  
The interface converter can generate a request for service on the bus when it  
receives the last serial terminator. To enable this feature, the Peripheral SRQ  
switch, located on the internal switch bank of SW1, must be enabled. When  
SRQ is enabled, the interface converter will assert the IEEE bus SRQ line and  
set serial poll status bits DIO7 and DIO3 when the last serial terminator is  
detected. The IEEE controller must perform a serial poll on the interface to  
clear the SRQ. If the Peripheral SRQ switch is in the disabled position, there  
will not be any indication in the serial-poll status byte that a serial terminator  
has been received.  
47  
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RS-232IEEE 488 INTERFACE CONVERTER  
DOT  
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
Switch  
Side  
View  
OPEN  
OPEN  
SRQ on Last  
Terminator Enabled  
SRQ on Last  
Terminator Disabled  
Figure 5-1. Switch SW1: Enabling or Disabling  
“SRQ on Last Terminator.”  
5.4 Serial-Poll Status-Byte Register  
The following shows and describes the serial-poll status information provided  
by the interface converter.  
DIO8  
IEEE Input Buffer NOT Empty  
This bit is set when the IEEE input buffer contains one  
or more data bytes.  
128  
64  
32  
16  
8
4
2
1
DIO8 DIO7 DIO6 DIO5 DIO4 DIO3 DIO2 DIO1  
Figure 5-2. Serial Poll Status Byte.  
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CHAPTER 5: Peripheral Operation  
DIO7  
rsv  
serial-poll status information  
This bit is defined by the IEEE 488 Specification and is used  
to indicate to the bus controller that the interface converter is  
the bus device that requested service. It is cleared when the  
interface is serial polled by the controller.  
DIO6  
DIO5  
Not Defined—Always “0”  
Serial Input Buffer NOT EMPTY  
This bit is set when the serial input buffer contains one or  
more data bytes which have not been sent out the IEEE bus.  
It is cleared, set to “0,” when the buffer is empty.  
DIO4  
DIO3  
IEEE Input Buffer Full  
When this bit is set, it indicates that the interface converter  
may hold off the controller on subsequent data transfers. The  
interface may continue to accept an additional 512 characters,  
depending on the size of the serial input buffer.  
Received Last Serial Terminator  
If the Peripheral SRQ feature is enabled, the interface  
converter will issue a request for service by asserting the SRQ  
line and setting this bit along with the rsv bit (DIO7). It is  
cleared, along with rsv, when serial polled by the controller.  
If this feature is not enabled, this bit is always “0.”  
DIO2  
DIO1  
Serial Handshake  
This bit indicates the present state of the serial handshake.  
If it is set to “1,” the serial device connected to the interface  
converter is capable of accepting serial data. If “0,” the RTS  
line is unasserted, if configured for hardware handshake, or  
the “X-OFF” character has been received, if configured for  
X-ON/X-OFF software handshake.  
Not Used—Always “0”  
49  
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RS-232IEEE 488 INTERFACE CONVERTER  
5.5 Use of Serial and Bus Terminators  
The interface converter can be configured to provide RS-232-to-IEEE-488 and  
IEEE-488-to-RS-232 terminator substitution. This is useful when interfacing a  
serial device that only issues carriage return [CR] as an output terminator to  
an IEEE controller that expects a carriage return followed by a line feed  
[CR-LF].  
In this previous example, the serial terminator should be selected for CR  
Only while the IEEE terminator is set to CR-LF. When a serial CR character is  
received it is discarded and substituted with an IEEE CR followed by an IEEE  
LF. In the IEEE to serial direction, the IEEE CR is unconditionally discarded.  
Upon receipt of the IEEE LF a serial CR is substituted.  
The interface converter can be made totally data-transparent by setting both  
the serial and IEEE terminators to be CR Only or LF Only. The choice of  
appropriate terminators may be determined by inspection of the serial device  
and IEEE controller’s instruction manuals. See Chapter 3 of this manual for  
instructions on selecting the interface converter’s serial and bus terminals.  
5.6 IEEE 488 Bus Implementation  
The interface converter implements many of the capabilities defined by the  
IEEE 488 1978 specification. These are discussed in the following sections.  
The interface converter does not support or respond to these bus uniline  
and multiline commands:  
Remote Enable (REN)  
Go to Local (GTL)  
Group Execute Trigger (GET)  
Local Lockout (LLO)  
Take Control (TCT)  
Parallel Poll (PP)  
Parallel Poll Configure (PPC)  
Parallel Poll Unconfigure (PPU)  
Parallel Poll Disable (PPD)  
50  
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CHAPTER 5: Peripheral Operation  
5.6.1 MY TALK ADDRESS (MTA)  
When the interface converter is addressed to talk, it retrieves data from  
the serial input buffer and outputs it to the IEEE 488 bus. It substitutes the  
selected IEEE bus terminators for the received serial terminators. The inter-  
face converter will continue to output serial input buffer data as long as the  
IEEE controller allows.  
5.6.2 MY LISTEN ADDRESS (MLA)  
When the interface converter is addressed to listen, it accepts data from the  
active talker and outputs this data through the serial interface. It substitutes  
the selected serial terminators for the received IEEE bus terminators.  
5.6.3 DEVICE CLEAR (DCL AND SDC)  
Device Clear resets the interface converter’s IEEE input and serial input  
buffers. Any pending data and Service Requests (SRQ), including the  
information they convey, are lost.  
5.6.4 INTERFACE CLEAR (IFC)  
IFC places the interface converter in the Talker/Listener Idle State. It clears  
any pending requests for service (SRQ). The condition which caused the SRQ  
remains unmodified.  
5.6.5 SERIAL POLL ENABLE (SPE)  
When Serial-Poll-Enabled, the interface converter sets itself to respond to a  
serial poll with its serial-poll status byte if addressed to talk. When the serial-  
poll byte is accepted by the controller, any pending SRQs are cleared. The  
interface converter will continue to try to output its serial-poll response until  
it is “Serial-Poll-Disabled” by the controller.  
5.6.6 SERIAL POLL DISABLE (SPD)  
Disables the interface converter from responding to serial polls by the  
controller.  
5.6.7 UNLISTEN (UNL)  
UNL places the interface converter in the Listener Idle State.  
5.6.8 UNTALK (UNT)  
UNT places the interface converter in the Talker Idle State.  
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RS-232IEEE 488 INTERFACE CONVERTER  
5.7 IEEE Address Selection  
SW3-1 through SW3-5 select the IEEE bus address of the interface converter  
when in the IEEE Peripheral mode. The address is selected by simple binary  
weighting with SW3-1 being the least significant bit and SW3-5 the most  
significant. The following figure shows the IEEE address of the interface  
converter set to 10.  
DOT  
1
2
3
4
5
6
7
8
0
1
Switch  
Side  
View  
OPEN  
0 x 16 -0  
1 x 8  
0 x 4  
1 x 2  
-8  
-0  
-2  
0 x 1 + -0  
IEEE Address = 10  
Figure 5-3. SW3 View for IEEE Address Selection.  
Listen Only Mode  
Listen Only is a special type of Peripheral operation. In the Listen Only Mode  
the interface converter accepts all data transmitted on the bus and transfers it  
out its serial port. The interface converter is set to Listen Only mode by  
setting its address to 31 (switches SW3-1 through SW3-5 all open).  
NOTE  
The 232-488 Converter does not support all of these functions. Refer  
back to controller mode (Section 4.1) and peripheral mode (Section 5.1)  
for more information about operation of this particular device.  
52  
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CHAPTER 6: IEEE 488 Primer  
6. IEEE 488 Primer  
6.1 History  
The IEEE 488 bus is an instrumentation-communication bus adopted by the  
Institute of Electrical and Electronic Engineers in 1975 and revised in 1978.  
The interface converter conforms to this most recent revision, designated  
IEEE 488-1978.  
Before this standard was adopted most instrumentation manufacturers  
offered their own versions of computer interfaces. This placed the burden  
of system hardware design on the end user. If your application required the  
products of several different manufacturers, then you might need to design  
several different hardware and software interfaces.  
The popularity of the IEEE 488 interface (sometimes called the General  
Purpose Interface Bus or GPIB) is due to the total specification of the  
electrical and mechanical interface as well as the data transfer and control  
protocols. The use of the IEEE 488 standard has moved the responsibility of  
the user from design of the interface to design of the high-level software that  
is specific to the measurement application.  
6.2 General Structure  
The main purpose of the GPIB is to transfer information between two or  
more devices. A device can either be an instrument or a computer. Before  
any information transfer can take place, it is first necessary to specify which  
will do the talking (send data) and which devices will be allowed to listen  
(receive data). The decision of who will talk and who will listen usually falls  
on the System Controller, which is the Active Controller at power-on.  
The System Controller is similar to a committee chairman. On a well-run  
committee, only one person may speak at a time and the chairman is  
responsible for recognizing members and allowing them to have their say.  
On the bus, the device that is recognized to speak is the Active Talker. There  
can only be one Talker at a time if the information transferred is to be clearly  
understood by all. The act of “giving the floor” to that device is called  
Addressing to Talk. If the committee chairman cannot attend the meeting, or  
if other matters require his attention, he can appoint an acting chairman to  
take control of the proceedings. For the GPIB, this device becomes the Active  
Controller.  
53  
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RS-232IEEE 488 INTERFACE CONVERTER  
At a committee meeting, everyone present usually listens. This is not the case  
with the GPIB. The Active Controller selects which devices will listen and  
commands all other devices to ignore what is being transmitted. A device is  
instructed to listen by being Addressed to Listen. This device is then referred  
to as an Active Listener. Devices that are to ignore the data message are  
instructed to Unlisten.  
The reason some devices are instructed to Unlisten is quite simple. Suppose a  
college instructor is presenting the day’s lesson. The students are told to raise  
their hands if the instructor has exceeded their ability to keep up while taking  
notes. If a hand is raised, the instructor stops his discussion to allow the slower  
students the time to catch up. In this way, the instructor is certain that each  
and every student receives all the information he is trying to present. Since  
there are a lot of students in the classroom, this exchange of information can  
be very slow. In fact, the rate of information transfer is no faster than the rate  
at which the slowest note-taker can keep up. The instructor, though, may have  
a message for one particular student. The instructor tells the rest of the class  
to ignore this message (Unlisten) and tells it to that one student at a rate  
which he can understand. This information transfer can then happen much  
quicker, because it need not wait for the slowest student.  
The GPIB transfers information in a similar way. This method of data transfer  
is called handshaking. More on this later.  
For data transfer on the IEEE 488, the Active Controller must:  
a)Unlisten all devices to protect against eavesdroppers.  
b)Designate who will talk by addressing a device to talk.  
c)Designate all the devices who are to listen by addressing those devices  
to listen.  
d)  
Indicate to all devices that the data transfer can take place.  
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CHAPTER 6: IEEE 488 Primer  
To Other Devices  
Device 1  
System Controller  
Able to Talk,  
Listen, and Control  
Data Bus  
Device 2  
DMM  
Able to Talk  
and Listen  
Data Byte  
Transfer  
Control  
Device 3  
Printer  
Only Able to Listen  
General  
Interface  
Management  
Device 4  
Frequency Counter  
Only Able to Talk  
DIO1-8  
DAV  
NRFD  
NDAC  
IFC  
ATN  
SRQ  
REN  
EOI  
Figure 6-1. IEEE 488 Bus Structure.  
6.3 Send It to My Address  
In the previous discussion, the terms Addressed to Talk” and “Addressed to  
Listen” were used. These terms require some clarification.  
The IEEE 488 standard permits up to 15 devices to be configured within one  
system. Each of these devices must have a unique address to avoid confusion.  
In a similar fashion, every building in town has a unique address to prevent  
one home from receiving another home’s mail. Exactly how each device’s  
address is set is specific to the device’s manufacturer. Some are set by DIP  
switches in hardware, others by software. Consult the manufacturer’s  
instructions to determine how to set the address.  
Addresses are sent with universal (multiline) commands from the Active  
Controller. These commands include My Listen Address (MLA), My Talk  
Address (MTA), Talk Address Group (TAG), and Listen Address Group  
(LAG).  
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RS-232IEEE 488 INTERFACE CONVERTER  
6.4 Bus Management Lines  
Five hardware lines on the GPIB are used for bus management. Signals on  
these lines are often referred to as uniline (single line) commands. The  
signals are “active low”: A low voltage represents a logical “1” (asserted),  
and a high voltage represents a logical “0” (unasserted).  
6.4.1 ATTENTION (ATN)  
ATN is one of the most important lines for bus management. If Attention is  
asserted, then the information contained on the data lines is to be interpreted  
as a multiline command. If it is not, then that information is to be interpreted  
as data for the Active Listeners. The Active Controller is the only bus device  
that has control of this line.  
6.4.2 INTERFACE CLEAR (IFC)  
The IFC line is used only by the System Controller. It is used to place all bus  
devices in a known state. Although device configurations vary, the IFC  
command usually places the devices in the Talk and Listen Idle states  
(neither Active Talker nor Active Listener).  
6.4.3 REMOTE ENABLE (REN)  
When the System Controller sends the REN command, bus devices will  
respond to remote operation. Generally, the REN command should be issued  
before any bus programming is attempted. Only the System Controller has  
control of the Remote Enable line.  
6.4.4 END  
OR  
IDENTIFY (EOI)  
The EOI line is used to signal the last byte of a multibyte data transfer. The  
device that is sending the data asserts EOI during the transfer of the last data  
byte. The EOI signal is not always necessary, as the end of the data may be  
indicated by some special character such as carriage return.  
The Active Controller also uses EOI to perform a Parallel Poll by  
simultaneously asserting EOI and ATN.  
6.4.5 SERVICE REQUEST (SRQ)  
When a device desires the immediate attention of the Active Controller it  
asserts SRQ. It is then the Controller’s responsibility to determine which  
device requested service. This is accomplished with a Serial Poll or a Parallel  
Poll.  
56  
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CHAPTER 6: IEEE 488 Primer  
6.5 Handshake Lines  
The GPIB uses three handshake lines in an “I’m ready—Here’s the data—I’ve  
got it” sequence. This handshake protocol assures reliable data transfer, at the  
rate determined by the slowest Listener. One line is controlled by the Talker,  
while the other two are shared by all Active Listeners. The handshake lines,  
like the other IEEE 488 lines, are active low.  
6.5.1 DATA VALID (DAV)  
The DAV line is controlled by the Talker. The Talker verifies that NDAC is  
asserted (active low) which indicates that all Listeners have accepted the  
previous data byte transferred. The Talker then outputs data on the bus and  
waits until NRFD is unasserted (high) which indicates that all Addressed  
Listeners are ready to accept the information. When NRFD and NDAC are  
in the proper state, the Talker asserts DAV (active low) to indicate that the  
data on the bus is valid.  
6.5.2 NOT READY FOR DATA (NRFD)  
This line is used by the Listeners to inform the Talker when they are ready to  
accept new data. The Talker must wait for each Listener to unassert this line  
(high), which they will do at their own rate when they are ready for more  
data. This assures that all devices that are to accept the information are ready  
to receive it.  
6.5.3 NOT DATA ACCEPTED (NDAC)  
The NDAC line is also controlled by the Listeners. This line indicates to the  
Talker that each device addressed to listen has accepted the information.  
Each device releases NDAC (high) at its own rate, but the NDAC will not  
go high until the slowest Listener has accepted the data byte.  
57  
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RS-232IEEE 488 INTERFACE CONVERTER  
1st Data Byte  
2nd Data Byte  
DIO-8  
(composite)  
DAV  
Source  
Valid  
Not  
Valid  
None  
Not  
Valid  
Valid  
All  
Ready  
None  
Ready  
All  
NFRD  
Acceptor  
Ready  
Ready  
None  
Accept  
All  
None  
All  
Accept  
NDAC  
Acceptor  
Accept Accept  
Figure 6-2. IEEE Bus Handshaking.  
6.6 Data Lines  
The GPIB provides eight data lines for a bit-parallel/byte-serial data transfer.  
These eight data lines use the convention of DIO1 through DIO8 instead of  
the binary designation of D0 to D7. The data lines are bidirectional and are  
active low.  
6.7 Multiline Commands  
Multiline (bus) commands are sent by the Active Controller over the data bus  
with ATN asserted. These commands include addressing commands for talk,  
listen, Untalk, and Unlisten.  
6.7.1 GO  
TO  
LOCAL (GTL)  
This command allows the selected devices to be manually controlled. ($01)  
6.7.2 LISTEN ADDRESS GROUP (LAG)  
There are 31 (0 to 30) listen addresses associated with this group. The 3 most  
significant bits of the data bus are set to 001, while the 5 least significant bits  
are the address of the device being told to listen.  
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CHAPTER 6: IEEE 488 Primer  
6.7.3 UNLISTEN (UNL)  
This command tells all bus devices to Unlisten. The same as Unaddressed to  
Listen. ($3F)  
6.7.4 TALK ADDRESS GROUP (TAG)  
There are 31 (0 to 30) talk addresses associated with this group. The 3 most  
significant bits of the data bus are set to 010 while the 5 least significant bits  
are the address of the device being told to talk.  
6.7.5 UNTALK (UNT)  
This command tells bus devices to Untalk. The same as Unaddressed to Talk.  
($5F)  
6.7.6 LOCAL LOCKOUT (LLO)  
Issuing the LLO command prevents manual control of the instrument’s  
functions. ($11)  
6.7.7 DEVICE CLEAR (DCL)  
This command causes all bus devices to be initialized to a predefined or  
power-up state. ($14)  
6.7.8 SELECTED DEVICE CLEAR (SDC)  
This causes a single device to be initialized to a pre-defined or power-up state.  
($04)  
6.7.9 SERIAL POLL DISABLE (SPD)  
The SPD command disables all devices from sending their Serial Poll status  
byte. ($l9)  
6.7.10 SERIAL POLL ENABLE (SPE)  
A device which is Addressed to Talk will output its Serial Poll status byte after  
SPE is sent and ATN is unasserted. ($18)  
6.7.11 GROUP EXECUTE TRIGGER (GET)  
This command usually signals a group of devices to begin executing a  
triggered action. This allows actions of different devices to begin  
simultaneously. ($08)  
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RS-232IEEE 488 INTERFACE CONVERTER  
6.7.12 TAKE CONTROL (TCT)  
This command passes bus control responsibilities from the current Controller  
to another device which has the ability to control. ($09 )  
6.7.13 SECONDARY COMMAND GROUP (SCG)  
These are any one of the 32 possible commands (0 to 31) in this group. They  
must immediately follow a talk or listen address. ($60 to $7F)  
6.7.14 PARALLEL POLL CONFIGURE (PPC)  
For devices capable of performing a Parallel Poll, this command determines  
which data bit they are to assert in response to a Parallel Poll ($05)  
6.7.15 PARALLEL POLL UNCONFIGURE (PPU)  
This disables all devices from responding to a Parallel Poll. ($15)  
6.8 More on Service Requests  
Most of the commands covered, both uniline and multiline, are the  
responsibility of the Active Controller to send and the bus devices to  
recognize. Most of these happen routinely by the interface and are totally  
transparent to the system programmer. Other commands are used directly by  
the user to provide optimum system control. Of the uniline commands, SRQ  
is very important to the test system, and the software designer has easy access  
to this line by most devices. Service Request is the method by which a bus  
device can signal to the Controller that an event has occurred. It is similar to  
an interrupt in a microprocessor-based system.  
Most intelligent bus peripherals have the ability to assert SRQ. A DMM might  
assert it when its measurement is complete, if its input is overloaded or for  
any of an assortment of reasons. A power supply might SRQ if its output has  
current limited. This is a powerful bus feature that removes the burden from  
the System Controller to periodically inquire, “Are you done yet?” Instead, the  
Controller says, “Do what I told you to do and let me know when you’re done”  
or “Tell me when something is wrong.”  
Since SRQ is a single line command, there is no way for the Controller to  
determine which device requested the service without additional information.  
This information is provided by the multiline commands for Serial Poll and  
Parallel Poll.  
60  
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CHAPTER 6: IEEE 488 Primer  
6.8.1 SERIAL POLL  
Suppose the Controller receives a service request. For this example, let’s  
assume there are several devices which could assert SRQ. The Controller  
issues an SPE (Serial Poll enable) command to each device sequentially. If  
any device responds with DIO7 asserted, it indicates to the Controller that it  
was the device that asserted, SRQ. Often the other bits will indicate why the  
device wanted service. This Serial Polling sequence, and any resulting action,  
is under control of the software designer.  
6.8.2 PARALLEL POLL  
The Parallel Poll is another way the Controller can determine which device  
requested service. It provides the who but not necessarily the why. When bus  
devices are configured for Parallel Poll, they are assigned one bit on the data  
bus for their response. By using the Status bit, the logic level of the response  
can be programmed to allow logical OR/AND conditions on one data line by  
more than one device. When SRQ is asserted, the Controller (under user’s  
software) conducts a Parallel Poll. The Controller must then analyze the eight  
bits of data received to determine the source of the request. Once the source  
is determined, a Serial Poll might be used to determine the why.  
Of the two polling types, the Serial Poll is the most popular due to its ability  
to determine the who and why. In addition, most devices support Serial Poll  
only.  
61  
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RS-232IEEE 488 INTERFACE CONVERTER  
7. Theory of Operation  
and Board Layout  
7.1 Theory of Operation  
The heart of the interface converter is a 6809 microprocessor (U101)  
supported by 8K bytes of firmware EPROM [U102 (2764)] and 32K bytes of  
static RAM [U103 (58256)]. A Versatile Interface Adapter [U104 (65B22)]  
is used to generate real-time interrupts for the firmware operating system.  
The front-panel annunciators are also driven by U104 through an inverter  
[U113 (74LS04)]. The IEEE 488 bus interface is accomplished by a  
TMS9914A [U106] controller with drivers U107 and U108. The serial  
interface is provided by the UART [6551 (U105)]. If RS-232 levels are chosen,  
they are provided by the RS-232 transceiver (U209). If RS-422 levels are  
selected, the differential driver [26LS30 (U207)] and receiver [26LS33  
(U208)] are used.  
The internal DIP switches [SW1, SW2, and SW3] are read via 74HCT244  
tri-state buffers [U201, U202 and U203]. Power is supplied by an external  
unregulated 9-volt wallmount supply. Regulation to the required +5 volts is  
provided by U206 [7805].  
Decoding of the microprocessor address space is accomplished with a  
Programmable Logic Array [U110 (16L8)]. The Memory space allocation is:  
Address  
$0000-$7FFF  
$A000-$A007  
$A800-$A807  
$B000-$B00F  
$B800  
Device  
U103  
U106  
U105  
U104  
U201  
U202  
U203  
U102  
Part Number  
58258  
Function  
Static RAM  
IEEE Controller  
UART  
9914A  
6551  
65B22  
74HCT244  
74HCT244  
74HCT244  
2764  
VIA  
SW1 (S201)  
SW2 (S202)  
SW3 (S203)  
Programmed EPROM  
$B801  
$B802  
$E000-$FFFF  
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CHAPTER 7: Theory of Operation and Board Layout  
7.2 Board Layout  
J104  
U110  
U101  
R102  
C124  
U107  
U108  
Figure 7-1. Component Layout of the  
Interface Converter’s Motherboard.  
63  
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RS-232IEEE 488 INTERFACE CONVERTER  
U201  
P204  
R205  
R201  
R202  
R203  
C201  
C202  
C203  
U205  
U206  
C205  
C209  
C207  
R207  
1
14  
C208  
Figure 7-2. Component Layout of the  
Interface Converter’s Serial I/O board.  
64  
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APPENDIX A: Sample Dumb-Terminal Program  
Appendix A. Sample Dumb-Terminal  
Program  
10  
REM ***  
DUMB-TERMINAL PROGRAM FOR THE interface  
converter  
20  
30  
40  
REM ***  
REM ***  
REM ***  
Running under IBM BASIC  
This Program allows direct interaction between the  
IBM PC and an IEEE bus device through the interface  
converter.  
50  
REM ***  
The interface converter must be configured as the  
IEEE bus  
controller and have Talk-Back on Terminator enabled.  
60  
70  
80  
90  
100  
REM ***  
REM ***  
REM ***  
REM ***  
CLS  
110 ' Open the serial communications port and set the serial parameters  
120 OPEN "COM1: 9600,n,8,2,cs,ds" AS 1  
130 ' Display any characters received from the COM1 port  
140  
IF LOC(1) THEN PRINT INPUT$ (LOC(1) ,1);  
150 ' Transmit any key presses from keyboard to the COM1 port and to  
the screen  
160 K$=INKEY$  
170 PRINT #1,K$; : PRINT K$;  
180 GOTO 140 ' Do it again  
65  
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RS-232IEEE 488 INTERFACE CONVERTER  
Appendix B. Character Codes and IEEE  
Multiline Messages  
$00  
0 $10  
16 $20  
32 $30  
48 $40  
64 $50  
80 $60  
96 $70  
112  
113  
114  
115  
116  
117  
118  
119  
120  
121  
122  
123  
124  
125  
126  
127  
NUL  
SOH  
STX  
ETX  
EOT  
ENQ  
ACK  
BEL  
BS  
DLE  
DC1  
DC2  
DC3  
DC4  
NAK  
SYN  
ETB  
CAN  
EM  
SP  
0
1
2
3
4
5
6
7
8
9
:
@
A
B
C
D
E
F
P
Q
R
S
T
U
V
W
X
Y
Z
[
`
a
b
c
d
e
f
p
16  
00  
17 $21  
16  
33 $31  
00  
49 $41  
SCG  
97 $71  
SCG  
81 $61  
$01  
1 $11  
65 $51  
!
q
17  
66 $52  
17  
34 $32  
SCG  
82 $62  
LLO  
2 $12  
01  
18 $22  
01  
50 $42  
GTL  
$02  
SCG  
98 $72  
"
r
18  
67 $53  
02  
51 $43  
02  
19 $23  
18  
35 $33  
SCG  
83 $63  
SCG  
99 $73  
$03  
$04  
3 $13  
4 $14  
#
$
%
&
'
s
19  
68 $54  
19  
36 $34  
SCG  
84 $64  
SCG  
100 $74  
03  
20 $24  
03  
52 $44  
t
20  
37 $35  
20  
69 $55  
DCL  
5 $15  
SCG  
101 $75  
SDC  
$05  
04  
21 $25  
04  
53 $45  
SCG  
85 $65  
u
21  
70 $56  
05  
22 $26  
21  
38 $36  
SCG  
86 $66  
SCG  
102 $76  
PPC  
$06  
PPU  
6 $16  
05  
54 $46  
v
22  
22  
39 $37  
06  
23 $27  
SCG  
87 $67  
SCG  
103 $77  
06  
55 $47  
$07  
$08  
7 $17  
8 $18  
71 $57  
G
H
I
g
h
i
w
SCG  
88 $68  
23  
40 $38  
07  
24 $28  
07  
56 $48  
23  
72 $58  
SCG  
104 $78  
(
x
08  
25 $29  
GET  
$09  
SPE  
9 $19  
SCG  
89 $69  
SCG  
105 $79  
24  
41 $39  
08  
57 $49  
24  
73 $59  
HT  
)
y
SPD  
10 $1A  
09  
26 $2A  
SCG  
106 $7A  
TCT  
$0A  
25  
42 $3A  
09  
58 $4A  
25  
74 $5A  
SCG  
90 $6A  
LF  
SUB  
ESC  
FS  
*
+
,
J
j
z
10  
59 $4B  
SCG  
91 $6B  
10  
27 $2B  
26  
43 $3B  
26  
75 $5B  
SCG  
107 $7B  
$0B  
$0C  
$0D  
$0E  
$0F  
11 $1B  
12 $1C  
13 $1D  
14 $1E  
15 $1F  
VT  
;
K
L
M
N
O
k
l
{
27  
76 $5C  
11  
60 $4C  
SCG  
92 $6C  
SCG  
108 $7C  
11  
28 $2C  
27  
44 $3C  
FF  
<
=
>
?
\
|
}
12  
29 $2D  
28  
45 $3D  
SCG  
93 $6D  
12  
61 $4D  
28  
77 $5D  
SCG  
109 $7D  
CR  
GS  
-
]
m
n
o
13  
62 $4E  
29  
78 $5E  
SCG  
110 $7E  
13  
30 $2E  
29  
46 $3E  
SCG  
94 $6E  
SO  
RS  
.
^
~
14  
63 $4F  
30  
47 $3F  
30  
79 $5F  
SCG  
95 $6F  
14  
31 $2F  
SCG  
111 $7F  
SI  
US  
/
_
DEL  
15  
UNT  
15  
SCG  
SCG  
UNL  
ACG = Addressed Command Group  
UCG = Universal Command Group  
LAG = Listen Address Group  
TAG = Talk Address Group  
SCG = Secondary Command Group  
66  
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APPENDIX B: Character Codes and IEEE Multiline Messages  
How To Read the Chart  
Hexadecimal  
Equivalent  
Decimal  
Equivalent  
ASCII Character  
Address or Command  
67  
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RS-232IEEE 488 INTERFACE CONVERTER  
Index  
Abbreviations  
DIO4...............................................49  
IEEE 488 .................................13  
DIO5...............................................49  
DIO6...............................................49  
DIO7...............................................49  
DIO8...............................................48  
Echo................................................19  
End Or Identify .............................56  
EOI22, 56  
Active Controller ...........................53  
Address Selection  
IEEE ........................................34  
Applications  
Plotter .....................................38  
Printer.....................................44  
ATN ................................................56  
Attention ........................................56  
Baud Rate.......................................16  
Blind Bus Data Transfers ..............46  
Board Layout ...........................63, 64  
Bus Management Lines  
Attention.................................56  
End Or Identify ......................56  
Interface Clear........................56  
Remote Enable.......................56  
Service Request.......................57  
CE Compliant  
Operating Conditions .....................2  
Character Codes ............................66  
Clear To Send................................27  
Configuration ................................14  
Connectors...............................26, 27  
Controlled Bus Data Transfers .....47  
Controller Features .......................24  
Controller Mode Operation .........32  
Controller Operation....................32  
Data Lines ......................................58  
Data Transfers  
Blind Bus.................................46  
Controlled Bus .......................47  
Data Valid.......................................57  
DAV ................................................57  
DCL ..........................................51, 59  
Device Clear.............................51, 59  
DIO1...............................................49  
DIO2...............................................49  
DIO3...............................................49  
Factory-Default Settings ..........14, 15  
Feature Selections .........................24  
Controller ...............................24  
Peripheral...............................25  
Features  
Talk Back ...........................34-36  
General Purpose  
Interface Bus..................................53  
GET ................................................59  
Go To Local ...................................58  
GPIB ...............................................53  
Ground...........................................28  
Group Execute Trigger.................59  
GTL ................................................58  
Handshake Lines...........................57  
Data Valid ...............................57  
Not Data Accepted.................57  
Not Ready For Data................57  
IEEE 488 Abbreviations.................13  
IEEE 488 Bus  
Implementation.............................50  
IEEE 488 Primer............................53  
IEEE Address Selection.....23, 34, 52  
IEEE Bus Terminator....................22  
IEEE Controller  
Mode ............................16, 22, 23, 32  
IEEE Data Transfers ......................46  
IEEE Multiline Messages...............66  
IEEE Peripheral.............................16  
IFC ...........................................51, 56  
Input Buffers..................................45  
Inspecting the Unit .......................14  
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INDEX  
Interface Clear.........................51, 56  
Interface Converter  
Package Contents ..........................14  
Parallel Poll....................................61  
Parallel Poll Configure..................60  
Parallel Poll Unconfigure .............60  
Peripheral Features .......................25  
Peripheral Mode......................22, 23  
Peripheral Operation....................45  
Plotter Applications.......................38  
Polling Types  
Parallel ....................................61  
Serial .......................................61  
POWER Indicator..........................31  
PPC60  
PPU.................................................60  
Printer Applications ......................44  
Receive Data...................................27  
Receive Data Plus...........................28  
Remote Enable ..............................56  
REN ................................................56  
Request To Send............................28  
RS-232 Signals.....................26-28, 39  
RS-422 Signals...........................26-28  
RTS/CTS............................20, 27, 28  
Sample Program ............................65  
SCG.................................................60  
SDC...........................................51, 59  
Secondary Command Group........60  
Selectable Functions......................14  
Selected Device Clear....................59  
Selecting an IEEE Address............52  
Selecting Terminator  
Connectors.....................................26  
Introduction...................................12  
LAG ................................................58  
LEDs ...................................31, 37, 43  
Listen Address Group....................58  
Listen Only...............................23, 52  
LLO ................................................59  
Local Lockout................................59  
MLA................................................51  
Mode  
Selection .................................22  
Modifying Factory Defaults...........16  
MTA................................................51  
Multiline Commands.........50, 56, 58  
Device Clear............................59  
Go To Local............................58  
Group Execute Trigger..........59  
Listen Address Group ............58  
Local Lockout.........................59  
Parallel Poll Configure ..........60  
Parallel Poll Unconfigure......60  
Secondary Command  
Group......................................60  
Selected Device Clear ............59  
Serial Poll Disable ..................59  
Serial Poll Enable...................59  
Take Control ..........................60  
Talk Address Group...............59  
Unlisten ..................................59  
Untalk .....................................59  
My Listen Address..........................51  
My Talk Address ............................51  
NDAC .............................................57  
Not Data Accepted ........................57  
Not Ready For Data .......................57  
NRFD..............................................57  
Operation  
Substitution....................................21  
Selecting the IEEE Address...........23  
Selecting the Mode........................22  
Self-Check ......................................31  
Send It to My Address ...................55  
Serial and IEEE Input Buffers ......45  
Serial and IEEE Terminator  
Substitution....................................33  
Serial Baud Rate ............................16  
Serial Echo.....................................19  
Serial Handshake...........................19  
Serial Interface ..............................25  
Controller ...............................32  
General .............................30, 31  
Peripheral...............................45  
Theory.....................................62  
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RS-232IEEE 488 INTERFACE CONVERTER  
Serial Parity ....................................18  
Serial Poll .......................................61  
Serial Poll Disable....................51, 59  
Serial Poll Enable ....................51, 59  
Serial Port Settings ........................16  
Serial Signal Descriptions .............26  
Serial Terminator ..........................21  
Serial-Poll Status  
UNT..........................................51, 59  
Untalk.......................................51, 59  
Wiring Diagrams............................29  
IBM AT with DB9  
Connector to Interface  
Converter................................30  
IBM PC with DB25  
Connectors to Interface  
Information..............................48, 49  
Serial-Poll Status-Byte  
Converter................................29  
Macintosh to Interface  
Register...........................................48  
Service Requests ......................57, 60  
Shorting Plug.....................25, 26, 42  
Signal Level Selection ...................26  
SPD51, 59  
SPE ...........................................51, 59  
Specifications  
Converter................................29  
X-ON/X-OFF.....................20, 27, 28  
General ...................................11  
IEEE-488 Interface .................10  
Serial Interface .......................10  
SRQ.................................................57  
SW1.............17, 18, 20, 24, 25, 35, 48  
SW2................................19, 21-24, 36  
SW3.....................................22, 23, 34  
System Controller..........................53  
TAG ................................................59  
Take Control..................................60  
Talk Address Group ......................59  
Talk-Back Features ........................34  
Talk-Back on Terminator..............35  
Talk-Back on Timeout...................36  
TCT ................................................60  
Terminator Substitution ...............21  
Serial and IEEE ......................33  
Terminators ...................................50  
Test Voltage ...................................28  
Theory of Operation .....................62  
Transmit Data ................................27  
Transmit Data Plus ........................28  
Uniline Commands .......................50  
UNL..........................................51, 59  
Unlisten..............................51, 54, 59  
Unpacking......................................14  
70  
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