Serial488A, Serial488A/OEM, Serial488A/512K

User’s Manual

IOtech, Inc.
25971 Cannon Road
Cleveland, OH 44146
Phone: (440) 439-4091
Fax: (440) 439-4093
E-mail: sales@iotech.com
Internet: http://www.iotech.com

Serial488A, Serial488A/OEM,
Serial488/512K User’s Manualp/n

SERIAL488/A-901, Rev 2.3© 1998 by IOtech, Inc. — Printed in the United States of America

WarrantyYour IOtech warranty is as stated on the product warranty card. You may contact IOtech byphone, fax machine, or e-mail in regard to warranty-related issues.
Phone: (440) 439-4091, fax: (440) 439-4093, email: sales@iotech.com

Limitation of Liability
IOtech, Inc. cannot be held liable for any damages resulting from the use or misuse of thisproduct.

Copyright, Trademark, and Licensing Notice
All IOtech documentation, software, and hardware are copyright with all rights reserved. Nopart of this product may be copied, reproduced or transmitted by any mechanical,
photographic, electronic, or other method without IOtech’s prior written consent. IOtech
product names are trademarked; other product names, as applicable, are trademarks of theirrespective holders. All supplied IOtech software (including miscellaneous support files,
drivers, and sample programs) may only be used on one installation. You may make archival
backup copies.

FCC Statement
IOtech devices emit radio frequency energy in levels compliant with Federal Communications
Commission rules (Part 15) for Class A devices. If necessary, refer to the FCC booklet How To Identify
and Resolve Radio-TV Interference Problems (stock # 004-000-00345-4) which is available from the
U.S. Government Printing Office, Washington, D.C. 20402.

CE Notice
Many IOtech products carry the CE marker indicating they comply with the safety and emissions
standards of the European Community. As applicable, we ship these products with a Declaration ofConformity stating which specifications and operating conditions apply.

Warnings and Cautions
Refer all service to qualified personnel. This caution symbol warns of possible personal injury or
equipment damage under noted conditions. Follow all safety standards of professional practice and therecommendations in this manual. Using this equipment in ways other than described in this manual canpresent serious safety hazards or cause equipment damage.
This warning symbol is used in this manual or on the equipment to warn of possible injury or death fromelectrical shock under noted conditions.
This ESD caution symbol urges proper handling of equipment or components sensitive to damage fromelectrostatic discharge. Proper handling guidelines include the use of grounded anti-static mats and wrist
straps, ESD-protective bags and cartons, and related procedures.

Specifications and Calibration
Specifications are subject to change without notice. Significant changes will be
addressed in an addendum or revision to the manual. As applicable, IOtech calibrates its
hardware products to published specifications. Periodic hardware calibration is not covered
under the warranty and must be performed by qualified personnel as specified in this manual.
Improper calibration procedures may void the warranty.

Quality Notice
IOtech has maintained ISO 9001 certification since 1996. Prior to shipment, we thoroughly test our
products and review our documentation to assure the highest quality in all aspects. In a spirit ofcontinuous improvement, IOtech welcomes your suggestions.

Introduction
1.1 Description
The Serial488A, Serial488A/OEM and Serial488/512K Bus Converters
provide transparent communication from a serial computer to an IEEE 488 printer,plotter or other device. They 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, it receives data from a serial host thenautomatically 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 thehost.
As an IEEE 488 to serial converter, it functions as a peripheral to an IEEE 488
controller. Data received from the controller is sent to the serial device, and data
received from the serial device is buffered for transmission to the IEEE 488 controller.
The converter can inform the host, by the serial poll status byte, that it has received
data from the serial device.
The Serial488A and Serial488A/OEM can communicate with RS-232 and RS422 devices by positioning configuration jumpers located within the unit. Bothdevices can communicate at selectable baud rates up to 57600 baud.
The Serial488/512K can communicate with RS-232 devices at selectable baudrates up to 19200 baud.
This manual will refer to all three interfaces as the Serial488A. Differences
between the Serial488A, Serial488A/OEM and Serial488/512K will be noted whereapplicable.

1.1

1.2 Serial488 and Serial488A Differences
The Serial488A is both a hardware and firmware upgrade to the Serial488.
When issuing product improvements, we try to maintain transparent compatibility.
Occasionally this is not possible. You should note the following differences between
the two products.
1.

The Serial488 allocated fixed serial and IEEE input buffers of 4000
characters. The Serial488A utilizes a 32,000 character buffer which is
dynamically allocated to the serial and IEEE input buffers as required.
Refer to Section 4.2 for more details

2.

The Serial488A has the ability to output RS-232 or RS-422 levels. The
levels used are internally selectable. Refer to Section 2.8 for details.

3.

As a peripheral, the Serial488A's serial poll status byte has beenchanged to include status of the serial handshake. Other minor changes
have also been included. Refer to Section 4.4 for a complete descriptionof the serial poll status byte.

4.

The internal switch settings for baud rate have been adjusted to include
57600 baud. Refer to Section 2.3 for the new switch settings.

1.3 Serial488A, Serial488A/OEM and Serial488/512K Differences
1. The Serial488A and Serial488A/OEM utilize a 32,000 character buffer
which is dynamically allocated to the serial and IEEE input buffers as required. The
Serial488/512K utilizes a 512,000 character buffer which is dynamically allocated tothe serial and IEEE input buffers as required.
2. The Serial488A and Serial488A/OEM have the ability to output RS-232 or
RS-422 levels. The Serial488/512K can only operate at RS-232 levels.
3. The Serial488A and Serial488A/OEM can operate at selectable baud rates
up to 57600 baud. The Serial488/512K can operate at selectable baud rates up to19200 baud.

1.2

1.4 Available Accessories
Additional accessories that can be ordered for the Serial488A include:
CA-7-1
CA-7-2CA-7-3CA-7-4
CA-11
CA-21
CA-22
CA-23
CN-20
CN-22
CN-23
ABC488
Rack488-3
Rack488-4
140-0920

1.5 foot IEEE 488 Cable
6 foot IEEE 488 Cable
6 foot shielded IEEE 488 Cable
6 foot reverse entry IEEE 488 Cable
12 foot IBM PC/XT/PS2 to Serial488A RS-232 Cable
12 foot Macintosh II/SE/Plus to Serial488A RS-232 Cable
12 foot Macintosh 512K to Serial488A RS-232 Cable
12 foot IBM AT to Serial488A RS-232 Cable
Right Angle IEEE 488 adapter, male and female
IEEE 488 Multi-tap bus strip, four female connectors in parallelIEEE 488 panel mount feed-through connector, male and female
IEEE 488 ABC switch
5-1/4" by 19" rack mount for one Serial488A
5-1/4" by 19" rack mount for two Serial488As
Instruction Manual

1.3

Specifications:$51,1*
Do not use this interface outdoors! The interface is intended for indoor use only! Outdoor
conditions could result in equipment failure, bodily injury or death!

:$51,1*
If equipment is used in any manner not specified in this manual, the protection provided by theequipment may be impaired. Please read this manual carefully.

&$87,21
Do not connect AC line power directly to the Serial488A. Direct AC connection will damage theequipment.

Serial488A
IEEE 488&$87,21The IEEE 488 terminal must only be used to control a non-isolated IEEE 488 system. The
common mode voltage (cable shell to earth) must be zero.

Terminal Installation Category: Standard: Not Applicable
CE: Category 1
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
Terminal Installation Category: Standard: Not Applicable
CE: Category 1
EIA RS-232C:
AB, BA, BB, CA, CB
EIA RS-422A:
Balanced voltage on TxD and RxD.
Character Set:
Asynchronous bit serial.
Output Voltage:±5 volts min (RS-422A). 5 volts typical (RS-232C).
Input Voltage:±3 volts min.; ±15v max.
Baud Rate:
Selectable 110, 300, 600, 1200, 1800, 2400, 3600, 4800, 7200,
9600, 19,200 and 57,600.
1.4

Data Format:
Duplex:Serial Control:
Terminators:
Connector:

Selectable 7 or 8 data bits; 1 or 2 stop bits; odd, even, mark,space and no parity on transmit.
Full with Echo/No Echo.
Selectable CTS/RTS or XON/XOFF.
Selectable CR, LF, LF-CR and CR-LF.
25-pin Sub-D male. DCE Configured.

GeneralTerminal Installation Category:
Data Buffer:
Indicators:
Power:
Dimensions:
Weight:Standard: Not Applicable
CE:
Category 1 for all terminals.
32,000 characters dynamically allocated.
LEDs for IEEE Talk and Listen, Serial Send and Receive, andPower.
An external power supply is provided with the Serial488A.
Input is 105 to 125VAC; 50 to 60 Hz, 10 VA Maximum.
188mm deep x 140mm wide x 68mm high (7.39" x 5.5" x2.68").
1.55 kg. (3.6 lbs).

Operating Environment:
Standard: Indoor use, 0° to 50°C; 0 to 70% R.H. to 35°C.
Linearly derate 3% R.H./°C from 35° to 50°C.
CE:
Indoor use at altitudes below 2000m, 0° to 40°C; 80% maximum
RH up to 31°C decreasing linearly 4% RH/°C to 40°C.
Controls:

Power Switch (external), IEEE and Serial parameter switches(internal). Jumper selection of RS-232 or RS-422 operation(internal).

*Specifications subject to change without notice.

1.5

Serial488A/OEM
IEEE 488
Implementation:
Terminators:
Connector:
Serial Interface
EIA RS-232C:
EIA RS-422A:
Character Set:
Output Voltage:
Input Voltage:
Baud Rate:
Data Format:
Duplex:Serial Control:
Terminators:
Connector:
GeneralData Buffer:
Indicators:
Power:
Dimensions:
Weight:Environment:
Controls:

C1, C2, C3, C4 and C28 controller subsets.(Serial to IEEE)
SH1, AH1, T6, TE0, L4, LE0, SR1, RL0, PP0, DC1, DT0, E1.
Selectable CR, LF, LF-CR and CR-LF with EOI.
Standard IEEE 488 connector with metric studs.
AB, BA, BB, CA, CB
Balanced voltage on TxD and RxD.
Asynchronous bit serial.
±5 volts min (RS-422A). 5 volts typical (RS-232C).
±3 volts min.; ±15v max.
Selectable 110, 300, 600, 1200, 1800, 2400, 3600, 4800, 7200,
9600, 19,200 and 57,600.
Selectable 7 or 8 data bits; 1 or 2 stop bits; odd, even, mark,space and no parity on transmit.
Full with Echo/No Echo.
Selectable CTS/RTS or XON/XOFF.
Selectable CR, LF, LF-CR and CR-LF.
25-pin Sub-D male. DCE Configured.
32,000 characters dynamically allocated.
LEDs for IEEE Talk and Listen, Serial Send and Receive, andPower.
User supplied +5 volts ±0.25% at 1 amp. Mating power
connector with 8 inch leads provided.
205mm deep x 115mm wide x 28mm high (8" x 4.5" x 1.1").
0.23kg. (0.5 lbs.)
0° - 50°C; 0 to 70% R.H. to 35°C. Linearly derate
3% R.H./°C from 35° to 50°C.
IEEE and Serial parameter switches. Jumper selection of
RS-232 or RS-422 operation.

*Specifications subject to change without notice.

1.6

Serial488/512K
IEEE 488-1978
Implementation:
Terminators:
Connector:
Serial Interface.
EIA RS-232C:
Character Set:
Output Voltage:
Input Voltage:
Baud Rate:
Data Format:
Duplex:Serial Control:
Terminators:
Connector:
GeneralData Buffer:
Indicators:
Power:
Dimensions:
Weight:Environment:
Controls:

C1, C2, C3, C4 and C28 controller subsets.(Serial to IEEE)
SH1, AH1, T6, TE0, L4, LE0, SR1, RL0, PP0, DC1, DT0, E1.
Selectable CR, LF, LF-CR and CR-LF with EOI.
Standard IEEE 488 connector with metric studs.
AB, BA, BB, CA, CB
Asynchronous bit serial.
5 volts typical (RS-232C).
±3 volts min.; ±15v max.
Selectable 110, 300, 600, 1200, 1800, 2400, 3600, 4800, 7200,
9600, and 19,200.
Selectable 7 or 8 data bits; 1 or 2 stop bits; odd, even, mark,space and no parity on transmit.
Full with Echo/No Echo.
Selectable CTS/RTS or XON/XOFF.
Selectable CR, LF, LF-CR and CR-LF.
25-pin Sub-D male. DCE Configured.
512,000 characters.
LEDs for IEEE Talk and Listen, Serial Send and Receive, andPower.
105-125V or 210-250V; 50-60 Hz, 10 VA Max.
188mm deep x 140mm wide x 68mm high (7.39" x 5.5" x2.68").
1.95 kg. (4.35 lbs).
0° - 50°C; 0 to 70% R.H. to 35°C. Linearly derate
3% R.H./°C from 35° to 50°C.
Power Switch (external)
IEEE and Serial parameter switches (internal).

*Specifications subject to change without notice.

1.7

1.6 Abbreviations
The following IEEE 488 abbreviations are used throughout this manual.
addr n
ATN
CA
CO
CR
data
DCL
GET
GTL
LA
LAG
LF
LLO
MLA
MTA
PE
PPC
PPU
SC
SDC
SPD
SPE
SRQ
TA
TAD
TCT
term
UNL
UNT
*

IEEE bus address "n"Attention line
Controller Active
Controller
Carriage Return
Data String
Device Clear
Group Execute Trigger
Go To Local
Listener Active
Listen Address GroupLine Feed
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
UntalkUnasserted

1.8

Getting Started
2.1 Inspection
The Serial488A was carefully inspected, both mechanically and electrically,prior to shipment. When you receive the interface, carefully unpack all items from theshipping carton and check for any obvious signs of physical damage which may haveoccurred during shipment. Immediately report any such damage found to the shipping
agent. Remember to retain all shipping materials in the event that shipment back to
the factory becomes necessary.
Every Serial488A is shipped with the following....
• Serial488A• 140-0920• Power Supply

IEEE 488 Bus Converter
Instruction Manual
9 Volt Regulated
TR-2; 115V or
TR-2E; 220V

Every Serial488A/OEM is shipped with the following....
• Serial488A/OEM• 140-0920

IEEE 488 Bus Converter
Instruction Manual

Every Serial488/512K is shipped with the following....
• Serial488/512K• 140-0920• Power Supply

IEEE 488 Bus Converter
Instruction Manual
9 Volt Regulated
TR-2; 115V or
TR-2E; 220V

2.1

2.2 Configuration
Three DIP switches internal to the Serial488A set the configuration of theinterface. 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 thefactory default settings which are:Serial Port:
9600 Baud
8 Data Bits
2 Stop Bits
No Parity
Serial Terminator = LF
Echo Disabled
RTS/CTS Handshake

IEEE:
Mode = IEEE 488 Controller
Address = 10
Bus Terminator = LF; EOI Disabled
Talk-back on Terminator Enabled
Talk-back on Time Out Enabled

SW3 Factory Default Settings
SW3

1 2 3 4 5 6 7 8

OPENIEEE Addr 10IEEE Term LF
EOI Disabled

2.2

Switch
Side
View

DOT

SW2 Factory Default Settings
SW2

1 2 3 4 5 6 7 8

Switch
Side
View

DOT

OPEN

Mode C
Talk Back on Time Out Enabled
LF
Serial Term
Echo No Echo
Parity No Parity

SW1 Factory Default Settings
SW1

1 2 3 4 5 6 7 8

Switch
Side
View

DOT

OPEN

Baud Rate 9600
Handshake RTS/CTS
Word Length 8 Data Bits
Talk Back on Term Enabled
Stop Bits 2 Stop Bits

The following drawings show the locations of switches SW1, SW2, and SW3 for
the Serial488A, Serial488A/OEM and the Serial488/512K. The top circuit board in
the Serial488A and the Serial488/512K is referred to as the I/O board.

2.3

Serial488A Switch Location - I/O Board

S203
SW3
S202
SW2

OPEN

SW3

SW2

S201
SW1

1 2 3 4 5 6 7 8SW1

1 2 3 4 5 6 7 8OPEN

1 2 3 4 5 6 7 8

OPEN

Serial488A/OEM Switch Location
S101
1 2 3 4 5 6 7 8

SW1
OPEN

SW-6-8S102
1 2 3 4 5 6 7 8

SW2
OPEN

SW-6-8S103
1 2 3 4 5 6 7 8

SW3
OPEN

SW-6-82.4

Serial488/512K SW1, SW2 Location - I/O Board
1 2 3 4 5 6 7 8

SW2
OPEN

C-5-.1SW-6-874HCT244
IC-39
RN-1-10K
1 2 3 4 5 6 7 8

SW1
OPEN

SW-6-8

Serial488/512K SW3 Location - Motherboard

1 2 3 4 5 6 7 8

OPEN

S102

2.5

SW3

Note that the Serial488A comes configured as an IEEE controller. In this mode
the Serial488A is designed to allow an RS-232 computer to communicate with anIEEE peripheral such as a plotter. This controller mode is described in detail in
Section 3.
The Serial488A may also be configured as an IEEE peripheral. As an IEEE
peripheral, the Serial488A allows an IEEE controller to communicate with an RS-232
device. The peripheral mode of operation is described in detail in Section 4.
To modify any of these defaults, follow this simple procedure: Disconnect thepower supply from the AC line and from the interface. Disconnect any IEEE or serial
cables prior to disassembly.
WARNING
Never open the Serial488A case while it isconnected to the AC line. Failure to observe thiswarning may result in equipment failure,personal injury or death.
Place the interface upside down on a flat surface. Remove the four (4) screws
located near the rubber feet. Return the interface to the upright position and carefully
remove the top cover. Modify those parameters which are appropriate for yourinstallation and then carefully re-assemble the interface using the reverse of theprocedure described.
2.3 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.
2.3.1 Serial Baud Rate Selection
Baud rate defines the number of serial bits per second transferred intoand out of the RS-232 interface. SW1-1 through SW1-4 determine theserial baud rate. The factory default baud rate is 9600 baud. Baud rates
may be selected from 110 to 57600 baud (110 to 19200 for the
Serial488/512K).

2.6

Refer to the following diagram for specific baud rates. Note: on the Serial488/512K,
selecting 57600 baud will have the same effect as selecting 19200 baud.
SW1 View for Serial Baud Rate Selection
1 2 3 4 5 6 7 8110

1 2 3 4 5 6 7 8

1800
OPEN

OPEN

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

110

2400
OPEN

OPEN

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

110

3600
OPEN

OPEN

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

135

4800
OPEN

OPEN

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

150

7200
OPEN

OPEN

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

300

9600
OPEN

OPEN

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

600

19200
OPEN

OPEN

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

1200

57600
OPEN

OPEN

2.7

Switch
Side
View

DOT

2.3.2 Serial Word Length Selection - 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.
SW1 View of Serial Word Length (Data Bits) Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

8 Data Bits

7 Data Bits

Switch
Side
View

DOT

2.3.3 Serial Stop Bit Selection
Switch SW1-8 determines the number of stop bits contained in eachserial character transmitted and received. The factory default is 2 stop bits.
SW1 View for Serial Stop Bit Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

1 Stop Bit

2 Stop Bits

Switch
Side
View

DOT

2.3.4 Serial Parity Selection
Serial Parity is selected with S2-6 through S2-8. The Serial488A
generates the selected parity during serial transmissions but it does notcheck parity on data that is received. The factory default is parity disabled.

2.8

SW2 View for Serial Parity Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Odd Parity

Mark Parity

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Even Parity

Space Parity

Switch
Side
View

DOT

1 2 3 4 5 6 7 8

OPEN

Parity Disabled

2.3.5 Serial Echo Selection
Serial data sent to the Serial488A will be echoed back to the serial
host if SW2-5 is set to the open position. Factory default is Echo Disabled.
SW2 View for Echo Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Echo Disabled

Echo Enabled

2.9

Switch
Side
View

DOT

2.3.6 Serial Handshake Selection
Switch SW1-5 is used to select between hardware [RTS/CTS] orsoftware [Xon/Xoff] serial handshake control.
With Xon/Xoff, the Serial488A issues an Xoff character [ASCII valueof $13] when its buffer memory is near full. When issued, there is greaterthan 1000 character locations remaining to protect against buffer overrun.
When it is able to accept more information it issues an Xon character[ASCII value of $11]. The Serial488A also accepts Xon/Xoff on transmit
from the serial host it is communicating with. RTS/CTS serial control
becomes inactive when Xon/Xoff is enabled. The RTS output is, however,set to an active high state. The CTS input is not used for this handshakeand may be left floating (unconnected).
With RTS/CTS, the Serial488A un-asserts RTS (low) when its buffer
memory is near full. When un-asserted, there is greater than 1000 character
locations remaining to protect against buffer overrun. When it is able toaccept more information it asserts (high) RTS. The Serial488A will nottransmit 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.

SW1 View for Serial Handshake Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

RTS/CTS

Xon/Xoff

2.10

Switch
Side
View

DOT

2.4 Terminator Selection
The Serial488A 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 the above 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 isdiscarded and substituted with an IEEE CR-LF. In the IEEE to RS-232 direction, theIEEE CR is unconditionally discarded. Upon receipt of the IEEE LF, a serial CR is
substituted.
The Serial488A can be made totally data transparent by setting both the serial
and IEEE terminators to be CR Only or LF Only.
2.4.1 Serial Terminator Selection
SW2-3 and SW2-4 select the serial terminators for the serial input andoutput. The factory default is LF Only.
SW2 View for Serial Terminator Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

CR Only

LF-CR

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

LF Only

CR-LF

2.11

Switch
Side
View

DOT

2.4.2 IEEE Bus Terminator Selection
SW3-6 through SW3-8 set the IEEE bus terminators used for data sentor received by the Serial488A. EOI, a line used to signal the end of amultiple 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.
SW3 View for IEEE Bus Terminator Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

CR Only

LF-CR

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

LF Only

CR-LF

1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

EOI Disabled

EOI Enabled

Switch
Side
View

DOT

2.5 Mode Selection
SW2-1 sets the major operating mode of the Serial488A. 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 Section 3 for more detailed
information on the controller mode of operation.

2.12

The Peripheral mode is used when interfacing a serial device to an IEEE
controller. Data which is sent by the IEEE controller to the Serial488A is transmitted
out its serial port. Data received from the serial device is buffered by the Serial488A
until read by the IEEE controller. Refer to Section 4 for more detailed information on
the peripheral mode of operation.
The factory default is the IEEE Controller mode, an RS-232 to IEEE converter.
SW2 View for Mode Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Controller Mode

Peripheral Mode

Switch
Side
View

DOT

2.6 IEEE Address Selection
SW3-1 through SW3-5 select the IEEE bus address of the Serial488A 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 Sections 4
and 3 respectively for additional information]. The address is selected by simple
binary weighting with SW3-1 being the least significant bit and SW3-5 the mostsignificant. The factory default is address 10.
Listen Only is a special type of Peripheral operation. In the Listen Only mode
the Serial488A accepts all data transmitted on the bus, ignoring any bus addressing,and transfers it out its serial port. The Serial488A is set to Listen Only mode bysetting its address to 31. If the IEEE address is set to 31 in the peripheral mode, it isadjusted to 30.

2.13

SW3 View for IEEE Address Selection0

1 2 3 4 5 6 7 81

Switch
Side
View

DOT

OPEN
=0
0 x 16
=8
1x8
=0
0x4
=2
1x2
0x1 + =0IEEE Address = 10

2.7 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.
2.7.1 Controller Features
In the IEEE Controller (RS-232 to IEEE 488 Converter) mode, SW17 is used to determine whether the interface should, after sending the IEEEbus terminators, address the attached bus device to talk. The factory default
is Talk-back On Terminator enabled.
SW2-2 selects whether the Serial488A should address the attached
bus device to talk when the Serial488A has nothing more to send to thatdevice. The factory default is Talk-back On Time Out enabled.
Refer to Section 3 for complete details on these features.

2.14

SW1 View for Controller Talk-Back on Terminator Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Talk Back on
Terminator Disabled

Talk Back on
Terminator Enabled

Switch
Side
View

DOT

SW2 View for Controller Talk-Back on Time-Out Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Talk Back on
Time Out Disabled

Talk Back on
Time Out Enabled

Switch
Side
View

DOT

2.7.2 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 indicatethat it has received the last switch selected serial terminator character fromthe serial device.
SW1 View for Peripheral SRQ on Last Serial Terminator
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

SRQ on Last
Terminator Disabled

SRQ on Last
Terminator Enabled

2.15

Switch
Side
View

DOT

2.8 Serial Interface
The Serial488A and Serial488A/OEM have 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/XT/AT/PS2 or compatible, the RS-232 level should be selected. If it
will be connected to a Macintosh 512K/Plus/SE/II, the RS-422 level should be used.
For connection to other computers, refer to the manufacturer's manual to determine
which levels are supported.
2.8.1 RS-232/RS-422 Signal Level Selection
The Serial488A's and Serial488A/OEM'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 it's socket.
Install the DIP jumper into the adjacent socket making certain that all of
the pins on the shorting plug are inserted correctly. The following diagrams
show which socket the jumper must be inserted for the desired operation.

J206

J205

RS-232 Signal Levels Selected - Serial488A

RS-422

Shorting Plug

RS-232

2.16

RS-232 Signal Levels Selected - Serial488A/OEM

J106
RS-232

Shorting Plug
J105

RS-4222.8.2 Serial Signal Descriptions
The Serial488A is equipped with a standard DB-25S connector on its
rear panel and requires a standard DB-25P mating connector. The
Serial488A's connector is configured as DCE type equipment for RS-232
communications, which means the Serial488A always transmits data on
Pin 3 and receives data on Pin 2. The following list describes the RS-232
and RS-422 signals provided on the Serial488A. Note: since theSerial488/512K does not support RS-422 communication, the pins labeled+TxD and +RxD are not used. Any reference to RS-422 communication
does not apply to the Serial488/512K.

2.17

GND
+VTEST
RTS
CTS
-TXD
-RXD

+VTEST

Rear View of the Serial488A's Serial Connector

1

+TXD

25

+RXD

13

14

-RxD

Receive Data - Input - Pin 2This 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 3This 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 andparity 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 theSerial488A 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 Serial488A will not transmit data out TxD while this line is un-asserted (low). If the RS-232 host is notcapable of driving this line it can be connected to the Vtest output(Pin 6) of the Serial488A. If Xon/Xoff handshake is selected, theCTS line is not tested to determine if it can transmit data.

2.18

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
Serial488A is not ready to accept it. When RTS/CTS handshakeis selected on the internal switches, the Serial488A will drive the
RTS output high when there are greater than 1000 character
locations available in its internal buffer. If the number of available
locations drops to less than 1000, the Serial488A will un-assert(low) this output. If Xon/Xoff handshake is selected, the RTS line
will be permanently driven active high.

Vtest

Test Voltage - Output - Pin 6This pin is connected to +5 volts through a 1K• resistor. It is also
common to Vtest on pin 9.

Gnd

Ground - Pin 7This pin sets the ground reference point for the other RS-232
inputs and outputs.

Vtest

Test Voltage - Output - Pin 9This 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 andparity selected by the internal switches. The signal level is hightrue and only connected to this pin when RS-422 operation is
selected. It is 180° 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 andonly connected to this pin when RS-422 operation is selected. It is
180° out of phase with -TxD.

2.19

2.8.3 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.
Macintosh to Serial488A Wiring Diagram (RS-422)
Macintosh to Serial488A
DB-9 Male

DB-25 Male

RTS

6
CTS 7
-TxD 5
Gnd 3-RxD 9+TxD 4+RxD 84 CTS
5 RTS
2 -RxD
7 Gnd
3 -Txd
14 +Rxd
16 +Txd

Macintosh Plus/SE/II to Serial488A Wiring Diagram (RS-422)
Macintosh II/SE/Plus to Serial488A
Mini DIN8 Male

DB-25 Male

RTS 1
CTS 2
-TxD 3
Gnd 4-RxD 5+TxD 6+RxD 84 CTS
5 RTS
2 -RxD
7 Gnd
3 -Txd
14 +Rxd
16 +Txd

2.20

IBM PC/XT/PS2 to Serial488A Wiring Diagram (RS-232)
IBM PC/XT/PS2 to Serial488A
DB-25 Female

DB-25 Male

-TxD 2-RxD 3
RTS 4
CTS 5
DSR 6
Gnd 7

2
3
4
5
6
7

-RxD
-TxD
CTS
RTS
Vtest
Gnd

IBM AT to Serial488A Wiring Diagram (RS-232)
IBM AT to Serial488A
DB-9 Female

DB-25 Male

DCD 1
-RxD 2-TxD 3
DTR 4
Gnd 5
DSR 6
RTS
CTS

3 -TxD
2 -RxD
7 Gnd

7
8

4 CTS
5 RTS

Note: Standard AT 9 Pin to 25 Pin adapter cables are not wired as shown above and will
not work with the Serial488A.

2.21

2.9 General Operation
Refer to the following sections for specific operational modes. This sub-section
gives a general test of functionality. After setting the power on defaults andreassembling the Serial488A, plug the power supply connector into the rear jack on
the interface.
CAUTION
Never install the power supply into the interface
while it is connected to AC line power. Failure
to observe this caution may result in damage to
the Serial488A.
WARNING
The power supply provided with the interface isintended for INDOOR USE ONLY. Failure toobserve this warning could result in equipment
failure, personal injury or death.
After installing the power supply connector into the interface, plug the power
supply into AC line power. Place the rear panel power switch in the ON [1] position.
All the front panel indicators should light momentarily while the Serial488A 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 indicates a RAM failure. Should such an error occur, turn the rear
panel switch to the OFF [0] position and retry the above procedure.
When the Serial488/512K is first powered on, it performs a self test which lasts
approximately 15 seconds. The front panel LED's will flash while the self test is
performed. If the unit is functional, all LED's except power should turn off after theself test is completed. If one or more LED's remains flashing, refer to the Hardware
Fault Identification Table to determine the cause of error.

2.22

Hardware Fault Identification Table - Serial488/512K
Error

Talk

Listen

Empty

Full

Power

No Error
No Error--Listen Only

off
off

off
on

on
on

off
off

on
on

No Power

off

off

off

off

off

Program Rom

on

on

on

on

on

Ram - U209
Ram - U210
Ram - U211
Ram - U212

blink
blink
blink
blink

off
off
off
off

off
on
off
on

off
off
on
on

on
on
on
on

Ram - U213
Ram - U214
Ram - U215
Ram - U216

blink
blink
blink
blink

on
on
on
on

off
on
off
on

off
off
on
on

on
on
on
on

Ram - U208
Ram - U201
Ram - U202
Ram - U203

off
off
off
off

off
off
on
on

off
on
off
on

blink
blink
blink
blink

on
on
on
on

Ram - U204
Ram - U205
Ram - U206
Ram - U207

on
on
on
on

off
off
on
on

off
on
off
on

blink
blink
blink
blink

on
on
on
on

Logic Error

blink

blink

blink

blink

on

2.23

If the front panel indicators do not flash and the POWER indicator does notremain 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 for proper installation.
If the problem is unresolved, refer to the Service Information section of this manual.
If proper operation is obtained, connect an interface cable to the rear of the
Serial488A [ 25-Pin Sub-D ]. Connect the other end to the host's serial port. Except
for connecting IEEE bus instruments, the Serial488A is installed and ready to use.
WARNING
The Serial488A makes its earth groundconnection through the serial interface cable. It
should only be connected to IEEE bus devices
after being first connected to the host. Failure to
do so may allow the Serial488A to float to a bus
device test voltage. This could result in damage
to the interface, personal injury or death.

2.24

Controller Operation
3.1 Controller Mode (Serial to IEEE) Operation
The IEEE Controller mode allows a serial RS-232 or RS-422 host device tosend data to a single IEEE bus peripheral or to multiple peripherals if they occupy thesame bus address. Applications include interfacing a listen-only or addressable IEEE
printer/plotter to a serial printer port.
Once the Serial488A has initialized itself after power-on, it waits for serial
input data. When received, it addresses the selected IEEE device to listen with thefollowing bus sequence:
ATN•UNL,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.
So long as the serial input buffer is not empty, the Serial488A will continue tosend data from it to the IEEE bus device. If the serial input buffer becomes emptied,
the Serial488A will command the IEEE bus device to talk if one of the talk backfeatures is enabled. This allows the Serial488A to be used as a controller with
devices, such as plotters or instruments, that return status and other information to thehost computer.
When the Serial488A addresses the IEEE bus device to talk it uses the following
bus sequence:
ATN•UNL,MLA,TAG,*ATN
The Serial488A then accepts data from the IEEE device and returns it to the hostuntil 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.

3.1

If the IEEE device has been addressed to talk but does not respond or finish
transmission by the time additional characters are received into the circular serial
input buffer, the talk sequence will be aborted to allow additional serial information to
be sent to the IEEE device.
3.2 Serial and IEEE Terminator Substitution
The Serial488A can be configured to provide serial to IEEE 488 and IEEE 488 toserial 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 previous example, 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 substituted with an IEEE CR followed by an IEEE LF. In the IEEE toserial direction, the IEEE CR is unconditionally discarded. Upon receipt of the IEEE
LF a serial CR is substituted.
The Serial488A can be made totally data transparent by setting both the serial
and IEEE terminators to be CR Only or LF Only. Refer to Section 2 for the properswitch settings for both the IEEE and serial terminators.
3.3 IEEE Address Selection
SW3-1 through SW3-5 select the IEEE bus address of the IEEE peripheral the
Serial488A will be communicating with. These switches set the address of the IEEE
device that will be controlled, not the address of the Serial488A. The address of the
Serial488A 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.

3.2

SW3 View for IEEE Address Selection0

1 2 3 4 5 6 7 81

Switch
Side
View

DOT

OPEN
=0
0 x 16
=8
1x8
=0
0x4
=2
1x2
0x1 + =0IEEE Address = 10

3.4 Talk Back Features
Two different switch selectable talk back features are included to provide bidirectional communication with the IEEE device. Whether either talk back feature
should be enabled is dependent on the application.
3.4.1 Talk Back On Terminator
SW1-7 is used to determine whether the interface should address theattached bus device to talk after sending the selected IEEE bus
terminator(s). This feature is commonly used to provide bi-directional
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.
SW1 View for Talk-Back on Terminator Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Talk Back on
Terminator Disabled

Talk Back on
Terminator Enabled

3.3

Switch
Side
View

DOT

When the serial input buffer becomes empty, the Serial488A 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 Serial488A from thebus device is sent to the serial host.
When the last IEEE bus terminator is detected from the IEEE device,
the Serial488A disables the device from sending additional information byasserting Attention (ATN) on the bus.
If the IEEE device does not responded or finish transmission by thetime additional characters are received into the serial input buffer, the talksequence will be aborted to allow additional serial information to be sent to
the IEEE device.
The following is an example of how this feature can be used tocommunicate with a single IEEE instrument. The program example iswritten in Basic on an IBM PC or compatible and communicates with aKeithley Model 196 DMM.
10
20
25
30
40
50
60
70
80
90
100
110
120
130
140
150

'
'
Example Program using Serial488A with' the Talk Back on Terminator Feature Enabled to'Communicate with a Keithley Model 196 DMM'' Open Basic's serial communications port
OPEN "COM1: 9600,N,8,2" AS 1
' 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 terminatorLINE INPUT #1, A$ ' Get Reading from 196
PRINT A$ ' print it on the screen
NEXT N
END

3.4

3.4.2 Talk Back On Time Out
SW2-2 selects whether the Serial488A should address the attached
bus device to talk when the Serial488A 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 Time Out enabled.
SW2 View for Talk-Back on Time-Out Selection
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

Talk Back on
Time Out Disabled

Talk Back on
Time Out Enabled

Switch
Side
View

DOT

If Talk-Back on Time-Out is enabled, then Serial488A waits
approximately 100 milliseconds after it detects its serial input buffer is
empty. If no serial character has been received by the end of this time, theIEEE bus device is addressed to talk. The choice of talk-back modes
depends strongly on the type of device and software being used. For mostplotter applications the Talk-back on Time-Out feature should beenabled.
When the last IEEE bus terminator is detected from the IEEE device,
the Serial488A disables the device from sending additional information byasserting Attention (ATN) on the bus. If the IEEE device does not respondor 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 sequencewith output data unless there has been a specific device dependentcommand sent to tell them what to say. If they have not been told what tosay, they say nothing.

3.5

The following is an example of how this feature can be used tocommunicate 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 istransmitted out of the serial (COM1) port. Any serial data which isreceived from the port is printed on the display.
10 'Dumb Terminal Program for the Serial488A
20 '
This
Programallowsdirectinteraction
between30 'the IBM-PC and an IEEE plotter through the
40 ' Serial488A. The Serial488A must have talk
back
50 '
on time out 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$(LOC(1),1);: GOTO 90
100 ' Transmit key presses to the COM1 port andscreen110 K$=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 Serial488A'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 theSerial488's front panel LEDs as you type the plotter commands.
Type the following HPGL output identify command on the keyboard.....
OI;
The plotter (HP 7470A) should immediately respond with.....
7470A
By typing the following HPGL 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;

3.6

3.5 Plotter Applications
To use the Serial488A 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 Xon/Xoff serial control. Since theseplotters are available with serial interfaces, the operator's manual ofyour 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 Serial488A'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 Time Out Enabled.

3.

Serial Terminators set to CR Only.

4.

IEEE Terminators set to CR Only with EOI enabled.

3.7

An IBM PC based Graphics System

The following shows the Serial488A's internal switch settings required to use a
Hewlett Packard 7580A plotter with AutoCad™ from AutoDesk on an IBM PC orcompatible. Because PC and compatibles output RS-232 levels, the shorting DIP
jumper should be set to the RS-232 position (J206).

J206

J205

Selecting RS-232 Signal Levels - Serial488A

RS-422

Shorting Plug

RS-232

3.8

Selecting RS-232 Signal Levels - Serial488A/OEM

J106
RS-232

Shorting Plug
J105

RS-422

3.9

SW3

Serial488A Settings For Use With HP 7580A Plotter on an IBM PC
1 2 3 4 5 6 7 8

Switch
Side
View

DOT

OPEN

IEEE Addr 5IEEE Term CR Only
EOI Enabled

SW2

1 2 3 4 5 6 7 8

Switch
Side
View

DOT

OPEN

Mode C
Talk Back on Time Out Enabled
Serial Term CR
Echo No Echo
Parity Even

SW1

1 2 3 4 5 6 7 8

OPEN

Baud Rate 9600
Handshake Xon/Xoff
Word Length 7 Data Bits
Talk Back on Terminator Enabled
Stop Bits 1 Stop Bit

3.10

Switch
Side
View

DOT

When using the Serial488A 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 configuration screen whichallows selection of baud rate, stop bits and parity. With this driver, the word length isfixed to 7 data bits with Xon/Xoff serial control. These non-modifiable defaults areplotter dependent. Refer to the plotter or driver manual for the defaults of the specificplotter.
For this example, 57600 baud with one stop bit and no parity has been chosen
for the serial data format.
MacPlot™ Configuration Screen

3.11

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).

Selecting RS-422 Signal Levels - Serial488A

J206

J205

Shorting Plug

RS-422

3.12

RS-232

Selecting RS-422 Signal Levels - Serial488A/OEM

J106
RS-232
J105
Shorting Plug

RS-422

3.13

The following illustrates the Serial488A's internal switch settings for use with
MacPlot utilizing the previously described format.

SW3

Serial488A Settings For Use With HP 7580A Plotter on a Macintosh
1 2 3 4 5 6 7 8

Switch
Side
View

DOT

OPEN

IEEE Addr 5IEEE Term CR
EOI Enabled

SW2

1 2 3 4 5 6 7 8

Switch
Side
View

DOT

OPEN

Mode C
Talk Back on Time Out Enabled
Serial Term CR
Echo No Echo
Parity No Parity

SW1

1 2 3 4 5 6 7 8

OPEN

Baud Rate 57600
Handshake Xon/Xoff
Word Length 7 Data Bits
Talk Back on Terminator Enabled
Stop Bits 1 Stop Bit

3.14

Switch
Side
View

DOT

After configuration, turn on the plotter and the Serial488A. The Serial488A'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 Serial488 has detected the plotter on the IEEE bus and has
addressed it to listen.
When the serial host begins to send the Serial488 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 theserial data format, word length, stop bits and parity.
3.6 Printer Applications
Most of the information given for plotter applications applies to applications forinterfacing IEEE 488 printers to a serial host. Some high end printers have asecondary command setting which must be disabled for the Serial488A to control
them. The Serial488 does not use secondary commands to control IEEE peripherals,
such as printers or plotters. Refer to the printer's instruction manual if the is a question
as to whether the printer requires secondary commands.

3.15

Peripheral Operation
4.1 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 Serial488A is buffered and transmitted out its serial port. Data
received from the serial device is buffered by the Serial488A until read by the IEEE
controller. The Serial488A and the Serial488A/OEM can buffer approximately
32,000 bytes of data from both the IEEE input and the serial input. The
Serial488/512K can buffer 512,000 bytes of data from both the IEEE input and theserial input.
The Serial488A will refuse to accept more data from the IEEE controller whenits 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 bynegating its Request To Send (RTS) output or by transmitting the Xoff ASCII
character. The serial handshake used is dependent on the handshake selection (Refer
to Section 2).
4.2 Serial and IEEE Input Buffers
Memory in the Serial488A is dynamically allocated for the serial input andIEEE 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 orqueue. 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 sothat it may be re-allocated when, and where, required.
There are approximately 250 available queues in the Serial488A and theSerial488A/OEM for a total of 32,000 bytes of buffer (character) space. Queues arecontinually 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.

4.1

When the serial input buffer requests one of the last 10 queues (1280 character
locations left), it signals the serial host that it should stop sending data. This isaccomplished by either un-asserting RTS or issuing "Xoff", depending on which serial
handshake control has been switch selected. When more than 10 queues become
available, it asserts RTS or issues "Xon".
The IEEE bus input signals that the IEEE input (or serial output) buffer is fullwhen 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 Serial488A stops accepting data from the bus. This bus
hold-off will only occur until additional queues (greater than 4) become available. At
that time it will resume accepting bus data.
4.3 IEEE Data Transfers
The following methods may be used by the IEEE controller when sending data
to the Serial488A:
4.3.1 Blind Bus Data Transfers
If the IEEE controller does not mind waiting an indefinite time fordata space in the buffer to become available, the data can simply be sent to
the Serial488A. This is referred to as blind data transfers because the IEEE
controller is blind as to whether or not the Serial488A is capable ofaccepting data. In this case, the bus controller's output data transfer will beheld off by the Serial488A if it is unable to buffer the data. It will resume
accepting IEEE input data when memory becomes available. This type ofcontrol might be appropriate in a single user environment.
To illustrate how this would appear, let's assume the Serial488A isconnected 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 theSerial488A at a rate of 5000 bytes per second. The data would betransferred 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 Serial488A.
If the controller is set to detect a data time-out error, then it will do so
if the Serial488A holds off IEEE input data transfers for too long. The
4.2

error can be used to alert the operator to the problem, such as a printer outof 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 isavailable in the Serial488A, the bus will hang until serial data is received.
If no serial data is received it will hang forever or until the controller timesout.
4.3.2 Controlled Bus Data Transfers
If the controller must avoid waiting for the serial device, it can 'serial
poll' the Serial488A. Serial poll is a method by which the controller caninquire the internal status of the interface without disturbing any data beingtransferred, slowing data transfers or locking up the bus. You should referto the programming manual of your controller to determine the method of
performing serial polls.
When serial polled, the Serial488A provides eight bits of status
information to the controller. The most significant bit [DIO8] of the
Serial488A'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 theserial device. If it is NOT EMPTY, the controller may avoid sending any
more data to the Serial488A. 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 toa logic "1" when there is 1280 or less locations in the buffer for data. It iscleared, 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.

4.3

When serial data is received, DIO5 of the Serial Poll byte is set, '1', toindicate to the IEEE controller that the serial input buffer is NOT EMPTY.
If 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 isread by the IEEE controller this bit is reset.
The Serial488A 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 enabled, the Serial488A 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 toclear the SRQ. If the Peripheral SRQ switch is in the disabled position,
there will still be an indication in the serial poll status byte that the last
serial input terminator was received, but Serial488A will not generate aservice request (SRQ).
SW1 View For Selecting SRQ on Last Terminator
1 2 3 4 5 6 7 8

1 2 3 4 5 6 7 8

OPEN

OPEN

SRQ on Last
Terminator Disabled

SRQ on Last
Terminator Enabled

Switch
Side
View

DOT

4.4 Serial Poll Status Byte Register
The following shows and describes the serial poll status information provided by
the Serial488A.
DIO8IEEE Input Buffer NOT Empty
This bit is set when the IEEE input buffer contains one or moredata bytes which have not been sent out the serial port. It iscleared, set to "0", when the buffer is empty.

4.4

Serial Poll Status Byte
128

64

32

16

8

4

2

1

Not Used - Al ways '0'

Serial Handsh ake

nput Terminat or
Last Serial I

IEEE Input Bu ffer Full

Buffer Not Em pty
Serial Input

Not Used - Al ways '0'

Request Servi ce - rsv bit

IEEE Input Bu ffer Not Empt y

DIO8 DIO7 DIO6 DIO5 DIO4 DIO3 DIO2 DIO1

DIO7

rsv
This bit is defined by the IEEE 488 Specification and is used toindicate to the bus controller that the Serial488A is the bus device
that requested service. It is cleared when the interface is serial
polled by the controller.

DIO6

Not Defined - Always "0"

DIO5

Serial Input Buffer NOT EMPTYThis bit is set when the serial input buffer contains one or moredata bytes which have not been sent out the IEEE bus. It iscleared, set to "0", when the buffer is empty.

4.5

DIO4

IEEE Input Buffer Full
When this bit is set, it indicates that the Serial488A may hold off
the controller on subsequent data transfers. The interface may
continue to accept an additional 512 characters but this isdependent on the serial input buffer size.

DIO3

Received Last Serial Terminator
This bit is set [1] when the Serial488A detects the last serial
terminator at its serial input. It remains set as long as there is atleast one serial terminator in the serial input buffer. If the
Peripheral SRQ feature is enabled, the Serial488A will issue arequest for service by asserting the SRQ line and also set the rsv
bit [DIO7]. The rsv bit is cleared, along with the SRQ line, whenserial polled by the controller. If there are additional serial
terminators in the serial input buffer, Serial488A will reassert the
SRQ line and rsv bit when the last IEEE 488 bus terminator is sent
to the IEEE 488 controller.

DIO2

Serial Handshake
This bit indicates the present state of the serial handshake. If it is
set to "1", the serial device connected to the Serial488A is capableof accepting serial data. If "0", the RTS line is unasserted, if
configured for hardware handshake, or the "Xoff" character has
been received, if configured for Xon/Xoff software handshake.

DIO1

Not Used - Always "0"

4.5 Use of Serial and Bus Terminators
The Serial488A 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,
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].

4.6

In the previous example, the serial terminator should be selected for CR Only
with the IEEE terminator set to CR-LF. When a serial CR character is received it isdiscarded and substituted with an IEEE CR followed by an IEEE LF. In the IEEE toserial direction, the IEEE CR is unconditionally discarded. Upon receipt of the IEEE
LF, a serial CR is substituted.
The Serial488A 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. For selection of the Serial488A's serial and bus terminators you
should refer to Section 2 of this manual.
4.6 IEEE 488 Bus Implementation
The Serial488A implements many of the capabilities defined by the IEEE 488
1978 specification. These are discussed in the following sections. The bus uniline andmultiline commands that the Serial488A does not support or respond to include:
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)
4.6.1 My Talk Address (MTA)
When the Serial488A is addressed to talk, it retrieves data from theserial input buffer and outputs it to the IEEE 488 bus. It substitutes theselected IEEE bus terminators for the received serial terminators. The
Serial488A will continue to output serial input buffer data as long as theIEEE controller allows.
4.6.2 My Listen Address (MLA)

4.7

When the Serial488A is addressed to listen, it accepts data from theactive talker and outputs this data through the serial interface. It substitutes
the selected serial terminators for the received IEEE bus terminators.
4.6.3 Device Clear (DCL and SDC)
Device Clear resets the Serial488A's IEEE input and serial input
buffers. Any pending data and Service Requests (SRQ), including theinformation they convey, are lost.
4.6.4 Interface Clear (IFC)
IFC places the Serial488A in the Talker/Listener Idle State. It clears
any pending requests for service (SRQ). The condition which caused the
SRQ remains unmodified.
4.6.5 Serial Poll Enable (SPE)When Serial Poll Enabled, the Serial488A sets itself to respond to aserial poll with its serial poll status byte if addressed to talk. When theserial poll byte is accepted by the controller, any pending SRQs arecleared. The Serial488A will continue to try to output its serial poll
response until it is 'Serial Poll Disabled' by the controller.
4.6.6 Serial Poll Disable (SPD)Disables the Serial488A from responding to serial polls by thecontroller.

4.8

4.6.7 Unlisten (UNL)UNL places the Serial488A in the Listener Idle State.
4.6.8 Untalk (UNT)
UNT places the Serial488A in the Talker Idle State.
4.7 IEEE Address Selection
SW3-1 through SW3-5 select the IEEE bus address of the Serial488A 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 Serial488A set to 10.
SW3 View for IEEE Address Selection0

1 2 3 4 5 6 7 81

Switch
Side
View

DOT

OPEN
=0
0 x 16
=8
1x8
=0
0x4
=2
1x2
0x1 + =0IEEE Address = 10

4.7.1 Listen Only Mode
Listen Only is a special type of Peripheral operation. In the Listen
Only mode the Serial488A accepts all data transmitted on the bus andtransfers it out its serial port. The Serial488A is set to Listen Only modeby setting its address to 31 (switches SW3-1 through SW3-5 all open).

4.9

4.8 IEEE to Serial Applications
The following program uses a Serial488A as an interface to a serial instrument
or host computer. The IEEE controller is an IBM PC running GWBasic with the
IOtech Personal488™ controller package. Communications are provided under directinteraction from the keyboard.
In this program example, key presses are detected and sent via the IEEE bus to
the Serial488A. The character is then sent to the serial device. Any incomming serial
characters are buffered by the Serial488A. The Serial488A is polled by the controller
for any data in the serial input buffer. When data is detected, it is read by thecontroller one character at a time and printed on the PC's screen. The IEEE address of
the Serial488A is 10.
10 ' Open Driver488 Files and initialize
20 OPEN "\DEV\IEEEOUT" FOR OUTPUT AS 1
30 IOCTRL #1,"BREAK"
40 PRINT #1,"RESET"
50 OPEN "\DEV\IEEEIN" FOR INPUT AS 2
60 ' Look for PC Key Press
70 K$ = INKEY$
80 IF K$="" THEN GOTO 110
90 ' Output Key Press to Serial488A
100 PRINT #1,"OUTPUT 10;";K$;
110 ' Test for Serial data
120 PRINT #1,"SPOLL 10" : INPUT #2,SPOLL
130 IF NOT (SPOLL AND 16) THEN GOTO 70
140 ' Enter One Byte From Serial488A and print it
150 PRINT #1,"ENTER 10 #1" : S$ = INPUT$(1,1) : PRINTS$;
160 GOTO 120 ' Try for more

4.10

IEEE 488 Primer
5.1 HISTORYThe IEEE 488 bus is an instrumentation communication bus adopted by theInstitute of Electrical and Electronic Engineers in 1975 and revised in 1978. The
Serial488A conforms to this most recent revision designated IEEE 488-1978.
Prior to the adoption of this standard, most instrumentation manufacturers
offered their own versions of computer interfaces. This placed the burden of system
hardware design on the end user. If his application required the products of several
different manufacturers, then he might need to design several different hardware andsoftware interfaces. The popularity of the IEEE 488 interface (sometimes called theGeneral Purpose Interface Bus or GPIB) is due to the total specification of theelectrical 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 fromdesign of the interface to design of the high level software that is specific to themeasurement application.
5.2 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 informationtransfer can take place, it is first necessary to specify which will do the talking (senddata) 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, at poweron, the Active Controller.
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 forrecognizing members and allowing them to have their say. On the bus, the device
which is recognized to speak is the Active Talker. There can only be one Talker at atime if the information transferred is to be clearly understood by all. The act of "giving
the floor" to that device is called Addressing to Talk. If the committee chairman can
not attend the meeting, or if other matters require his attention, he can appoint an
acting chairman to take control of the proceedings. For the GPIB, this device becomes
the Active Controller.
At a committee meeting, everyone present usually listens. This is not the casewith the GPIB. The Active Controller selects which devices will listen and
5.1

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 which are to ignore the data message are instructed to Unlisten.
The reason some devices are instructed to Unlisten is quite simple. Suppose acollege instructor is presenting the day's lesson. Each student is told to raise theirhand if the instructor has exceeded their ability to keep up while taking notes. If ahand 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 theclassroom, 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 thatone student at a rate which he can understand. This information transfer can thenhappen much quicker, because it need not wait for the slowest student.
The GPIB transfers information in a similar way. This method of data transfer iscalled handshaking. More on this later.
For data transfer on the IEEE 488, the Active Controller must…
a)
b)
c)
d)

Unlisten all devices to protect against eavesdroppers.
Designate who will talk by addressing a device to talk.
Designate all the devices who are to listen by addressing thosedevices to listen.
Indicate to all devices that the data transfer can take place.

5.2

To Other Devices

Device 1
System Controller
Able to Talk,
Listen, and Control
Data Bus
Device 2
DMM
Data Byte
Transfer
Control

Able to Talk
and Listen

Device 3
Printer
Only Able to Listen

GeneralInterfaceManagement

Device 4
Frequency Counter
Only Able to Talk}

DIO1-8

DAV
NRFD
NDAC

IEEE 488 Bus Structure

IFC
ATN
SRQ
REN
EOI

Figure 5.1

5.3

5.3 SEND IT TO MY ADDRESSIn 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 asimilar fashion, every building in town has a unique address to prevent one home fromreceiving another home's mail. Exactly how each device's address is set is specific to
the product's manufacturer. Some are set by DIP switches in hardware, others bysoftware. 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).
5.4 BUS MANAGEMENT LINES
Five hardware lines on the GPIB are used for bus management. Signals on theselines are often referred to as uniline (single line) commands. The signals are active
low, i.e. a low voltage represents a logic "1" (asserted), and a high voltage represents alogic "0" (unasserted).
5.4.1 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 beinterpreted as a multiline command. If it is not, then that information is to beinterpreted as data for the Active Listeners. The Active Controller is the
only bus device that has control of this line.

5.4

5.4.2 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, theIFC command usually places the devices in the Talk and Listen Idle states(neither Active Talker nor Active Listener).
5.4.3 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.
5.4.4 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 bysimultaneously asserting EOI and ATN.
5.4.5 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.

5.5

5.5 HANDSHAKE LINESThe 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 theother two are shared by all Active Listeners. The handshake lines, like the otherIEEE 488 lines, are active low.
5.5.1 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 haveaccepted 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) toindicate that the data on the bus is valid.
5.5.2 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 tounassert 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.
5.5.3 Not Data Accepted (NDAC)
The NDAC line is also controlled by the Listeners. This line indicatesto the Talker that each device addressed to listen has accepted theinformation. 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.

5.6

1st Data Byte

2nd Data Byte

DIO1-8(composite)
DAV

Valid

SourceNRFD
Acceptor

NDAC
Acceptor

All
Ready

Not
Valid

None
Ready

None
Accept

Valid

All
Ready

All
Accept

Not
Valid

None
Ready

None
AcceptAll
AcceptIEEE Bus Handshaking
5.6 DATA LINESThe 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.
5.7 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.
5.7.1 Go To Local (GTL)
This command allows the selected devices to be manually controlled.
($01)

5.7

5.7.2 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 leastsignificant bits are the address of the device being told to listen.
5.7.3 Unlisten (UNL)
This command tells all bus devices to Unlisten.
Unaddressed to Listen. ($3F)

The same as

5.7.4 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 leastsignificant bits are the address of the device being told to talk.
5.7.5 Untalk (UNT)This command tells bus devices to Untalk. The same as Unaddressed to
Talk. ($5F)
5.7.6 Local Lockout (LLO)
Issuing the LLO command prevents manual control of the instrument's
functions. ($11)
5.7.7 Device Clear (DCL)
This command causes all bus devices to be initialized to a pre-definedor power up state. ($14)

5.8

5.7.8 Selected Device Clear (SDC)
This causes a single device to be initialized to a pre-defined or power up
state. ($04)
5.7.9 Serial Poll Disable (SPD)The SPD command disables all devices from sending their Serial Pollstatus byte. ($19)
5.7.10 Serial Poll Enable (SPE)A device which is Addressed to Talk will output its Serial Poll statusbyte after SPE is sent and ATN is unasserted. ($18)
5.7.11 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)
5.7.12 Take Control (TCT)This command passes bus control responsibilities from the current
Controller to another device which has the ability to control. ($09)
5.7.13 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)

5.9

5.7.14 Parallel Poll Configure (PPC)This configures devices capable of performing a Parallel Poll as towhich data bit they are to assert in response to a Parallel Poll. ($05)
5.7.15 Parallel Poll Unconfigure (PPU)This disables all devices from responding to a Parallel Poll. ($15)

5.8 MORE ON SERVICE REQUESTS
Most of the commands covered, both uniline and multiline, are the responsibilityof the Active Controller to send and the bus devices to recognize. Most of thesehappen 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 systemand 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 mightassert it when its measurement is complete, if its input is overloaded or for any of anassortment 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 iswrong."
Since SRQ is a single line command, there is no way for the Controller todetermine which device requested the service without additional information. This
information is provided by the multiline commands for Serial Poll and Parallel Poll.

5.10

5.8.1 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 theController that it was the device that asserted SRQ. Often times the otherbits will indicate why the device wanted service. This Serial Polling
sequence, and any resulting action, is under control of the software
designer.
5.8.2 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 biton the data bus for their response. By using the Status bit, the logic level ofthe response can be programmed to allow logical OR/AND conditions on
one data line by more than one device. When SRQ is asserted, theController (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 Pollmight be used to determine the why.
Of the two polling types, the Serial Poll is the most popular due to its ability todetermine the who and why. In addition, most devices support Serial Poll only.

5.11

Service Information
6.1 Factory Service
If problems are encountered in using the Serial488A you should first telephone
the factory. Many problems can be resolved by discussing the problems with ourapplications department. If the problem cannot be solved by this method, you will be
instructed as to the proper return procedure.
6.2 Theory of Operation
The Heart of the Serial488A 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 provide 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
wall mount supply. Regulation to the required +5 volts is provided by U206 [7805].

6.1

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
$B801
$B802
$E000-$FFFF

Device
U103
U106
U105
U104
U201
U202
U203
U102

Part Number
58258
9914A
6551
65B22
74HCT244
74HCT244
74HCT244
2764

6.2

Function
Static RAM
IEEE Controller
UART
VIA
SW1 (S201)
SW2 (S202)
SW3 (S203)
Programmed EPROM

6.3 Serial488A Mother Board Component Layout

R104

C113

C103

U103

C110

U110

C102

C117

U102

+

+

C101

C106

U106
C107

C108

U108

J101

6.3

D103

D104

U113

C105

R101

Y101

C124
R102

D105

U104

C118

U101

J104
D101

U107

D106

D102

C104

U105

6.4 Serial488A I/O Board Component Layout
CN-11

BLK

C205

RED

U207

U208

C207

P204

U206

C210

C208

R205

U205

S205

J204

C206

1
14

U201

R206
J205

U203

U202

C203

C202

C201

J203
C212 C213++
CN-8-25

+

+

U209

J206

R207

R203

R202

J202

1

1

2

2

2

3

3

4

4

5

5

OPEN

OPEN

5

6

6

6

SW-2024

SW-203

3

13
25

1

OPEN

SW-201

C209

R201

C211 C214

7

7

7
8

8

8

S201
SW1

S202
SW2

S203
SW3

6.4

CA-19-8

6.5 Replaceable Parts List - Serial488A
Schematic

Part Number

Description

C101-C108
C110,C113
C117,C118
C124
C211-C214
C201-C203
C205-C209
C210
D101
D102-D106
J101
J104
J201
J204
J205
P204
R101
R102
R104
R201-R203
R205
R206
R207
S201-S203
S205
U101
U102
U103
U104
U105
U106
U107
U108
U110
U113
U201-U203
U205
U206
U207
U208
U209
Y101

C-5-.1
C-5-.1
C-5-15p
C-2-10C-2-10C-5-.1
C-5-.1
C-5-1
RF-1
DD-2
CN-2
CN-5-13CN-11
CN-8-25
CA-19-8
CA-6
R-1-68K
RN-4-4.7K
RN-2-470
RN-1-10K
R-2-39R-1-100
R-1-1K
SW-6-8
SW-11
IC-1
Serial488A-600
IC-78
IC-23
IC-16
IC-3
IC-4
IC-5
Macro488-601
IC-33
IC-39
IC-21
IC-30
IC-38
IC-36
IC-82
CR-4

Ceramic, 25v
Ceramic, 25v
Ceramic, 25v
Electrolytic, 25v
Electrolytic - 25v
Ceramic, 25v
Ceramic, 25v
Ceramic, 25v
Small Signal Diode
Red PC Mount
IEEE 488 Connector
13 x 2 0.1" Header
9 Volt Power JackPC Mount Female DB-25
8 Pos. DIP Jumper
26 Conductor Ribbon Assembly
68KΩ, 1/4w carbon
4.7KΩ x 7 SIP
470Ω x 5 SIP
10KΩ x 9 SIP
39Ω, 1w carbon
100Ω, 1/4w carbon
1KΩ, 1/4w carbon
8 Pole DIP
8 Pole DT Push Push
MC68B09P Microprocessor
Programmed EPROM
84256-15 32K x 8 CMOS SRAM
65B22 Versitile Interface Adapter
R6551AP UARTTMS9914ANL IEEE Controller
SN75160BN IEEE Driver
SN75162BN IEEE Driver
Programming Equation - 16L8 PAL
74LS04 Hex Inverter
74HCT244 Octal Buffer
SN74LS139 Dual Decoder
LM7805CT Regulator - +5v
26LS30 RS-423 Driver
26LS33 RS-422 Receiver
LT1081 RS-232 Transceiver
7.3728 MHz Crystal

6.5

DATUM 'A'

6.7
0.20

DATUM 'B'

0.20

1.13

2.97

4.10

4.30

I
E
E
E
4
8
8

0.050

Mounting
Holes

0.156 Dia [4 Places]

7.80

7.60

Mounting
Holes

0.050

R
S
2
3
2
C

1.125

2.975

6.7 Serial488A/OEM Mechanical Dimensions

IEEE Connector Mounting & Hole Punch Out
C
G

0.200 Radius typDdia. 2places

CL

F
CL

E

0.320

B

PCB

10° typ

A

B

C

A
D

1.842

0.921

1.578

0.789

E

F

G

0.640

0.320

0.194

Note: Does not imply orientation

6.8

6.8 Replaceable Parts List - Serial488A/OEM
Schematic

Part Number

Description

C101-C114
C116-C118
C119,C120
C121-C125
C126
D101
D102-D106
J101
J102
J103
J104
J105
R101
R102
R103
R104
R105
R106-R108
S101-S103
U101
U102
U103
U104
U105
U106
U107
U108
U109
U110
U111
U112-U114
U116
U117
U118
Y101

C-5-.1
C-5-.1
C-5-15p
C-2-10
C-5-1
RF-1
DD-2
CN-2
CN-5-12CN-32-2
CN-8-25
CA-19-8
RN-4-4.7K
R-1-68K
R-1-1K
RN-2-470
R-1-100
RN-1-10K
SW-6-8
IC-1
Serial488A-600
IC-78
IC-23
IC-16
IC-3
IC-4
IC-5
Macro488-601
IC-33
IC-21
IC-39
IC-38
IC-36
IC-82
CR-4

Ceramic, 25v
Ceramic, 25v
Ceramic, 25v
Electrolytic - 25v
Ceramic, 25v
Small Signal Diode
Red PC Mount
IEEE 488 Connector
12 x 2 0.1" Header
2 Position power connector
PC Mount Female DB-25
8 Pos. DIP Jumper
4.7KΩx 7 SIP
68KΩ, 1/4w carbon
1KΩ, 1/4w carbon
470Ω x 5 SIP
100Ω, 1/4w carbon
10KΩ x 9 SIP
8 Pole DIP
MC68B09P Microprocessor
Programmed EPROM
84256-15 32K x 8 CMOS SRAM
65B22 Versitile Interface Adapter
R6551AP UARTTMS9914ANL IEEE Controller
SN75160BN IEEE Driver
SN75162BN IEEE Driver
Programming Equation - 16L8 PAL
74LS04 Hex Inverter
SN74LS139 Dual Decoder
74HCT244 Octal Buffer
26LS30 RS-423 Driver
26LS33 RS-422 Receiver
LT1081 RS-232 Transceiver
7.3728 MHz Crystal

6.9

6.9 Serial488/512K Motherboard Component Layout

SW-6-85

6 7

8

RN-1-10K

OPEN

1 2 3 4

R103
RN-2-470

C105

C-5-.1

Macro488-601

C103

C110

U103
C-5-.1

C102
C-5-.1

C114

C123

C117

C-5-.1

U102

C122

+

C120

+
+
C119 C121

+

C-5-1
CR-4

SO-1-40
Y101

Jumper++C101
C-5-.1

C106
C-5-.1

R106

R-1-1K

6.10

R104

C-5-.1SO-1-20RF-1

R-1-68K
R101
D101

LT1081
IC-82
C118

RN-4-4.7K

DD-2

U113
C113

SO-1-28

D103

D104

DD-2
C-5-.1
D105

DD-2

74LS04

S102
CN-5-13

SW3
U104
C-5-.1SO-1-28
C-5-15p

C124
R102

C-2-10 (4)C-2-10
U101

U110
84256
IC-78

16L8 PAL
SO-1-28

IC-33
6522
IC-23

C104

U105

J104
6551
IC-16

D106

DD-2

D102

DD-2

SO-1-40

C-5-.1

6.11
74HCT240
IC-48

.33

75162
IC-5
C-5-.1

CN-2
C-5-.1
C-5-.1

U208

41256-15

.33

U209

41256-15

U210

.33

RN-3-47

RN-3-47

C-5-.1

U20141256-15

U20241256-15.33

IC-3
74HCT00
IC-34

68B09

74HCT240
IC-48

7 8

IC-1

U203

41256-15.33

74LS139
IC-21

6

C-5-.141256-15

.33

U211

41256-15

U20441256-15.33

74LS04IC-33

574LS373
IC-32

U212

41256-15.33

74HCT240IC-48

474LS138
IC-8

3

OPEN

7 8

C-5-.1
74HCT244
IC-39

U205

41256-15

U20641256-15

U207

.33

74LS08
IC-49

2

6

75160
IC-4
U213

.33

RN-1-10K

1

5

SO-1-4041256-15

U21441256-15.33

SW-6-8U215

C-2-100+
41256-15+.33

74HCT240
IC-48

474HCT244IC-39

41256-15.33

RN-1-10K

U216

41256-15

.33

J101

SW-6-83

C-5-.1

2

C-5-.1

1

SW1
OPEN

C-5-.1

6.10 Serial488/512K I/O Board Component Layout
.33

.33

SW2

TMS9914ANL
C-5-.1
C-5-.1
C-5-.1
C-5-.1

C-5-.1
C-5-.1

6.11 Replaceable Parts List - Serial488/512K
Schematic

Part Number

Description

C101-C105
C110
C113,C114
C117,C118
C119-C122
C123
C124
C201-C216
C217-C232
C233

C-5-.1
C-5-.1
C-5-.1
C-5-15p
C-2-10
C-5-1
C-2-10C-5-.33
C-5-.1C-2-100

0.1µF, 25v ceramic
0.1µF, 25v ceramic
0.1µF, 25v ceramic
15pF, ceramic
10µF, 25v electrolytic
1µF, 25v ceramic
10µF, 25v electrolytic
0.33µF, 25v ceramic
0.1µF, 25v ceramic
100µF, 25v electrolytic

D101
D102-D106

RF-1
DD-1

1N914 diodeLED, Dialight #550-2406

J101
J102
J103

CN-11
CN-19-25
CN-2

Power Connector SWCR #712A
25 Pin Sub-D Female
IEEE Connector

J202-J203

CA-20

20 Circuit Jumper Cable

R101
R102
R103
R104
R106

R-1-68K
RN-4-4.7K
RN-1-10K
RN-2-470
R-1-1K

68KΩ, 1/4w, 10% carbon
4.7KΩ x 7 SIP Network
10KΩ X 9 SIP Network
470Ω X 5 SIP Network
1KΩ, 1/4w, 10% carbon

R201-R202
R204,R205

RN-3-47
RN-1-10K

47Ω X 8 DIP Network
10KΩ x 9 SIP Network

S101
S102
S201,S202

SW-8
SW-6-8SW-6-8

Power Switch
8 pole DIP switch
8 pole DIP switch

U102
U103
U104
U105

IC-10
IC-78
IC-23
IC-16

2764-35 EPROM
84256 CMOS RAM
6522 VIA
6551 UART

U110
U113
U114

Macro488-601
IC-33
IC-82

Programmed 16L8 PAL
74LS04
LT1081

6.12

SchematicPart Number

Description

U201-U216
U217
U218 ,U219
U220-U223
U224
U225
U226
U227
U228
U229
U230
U231
U232

IC-46
IC-50
IC-14
IC-48
IC-1
IC-34
IC-21
IC-8
IC-3
IC-33
IC-49
IC-5
IC-4

256K DRAM 150NS
74LS373 Octal Tri-State D
74HCT244 Octal Buffer
74HCT240 Inverting Buffer
MC68B09 Microprocessor
74HCTOO Quad NAND
74LS139 Dual Decoder
74LS138 Decoder
TMS9914ANL
74LS04 Hex Inverter
74LS08 Quad AND Gate
75162 IEEE Driver
75160 IEEE Driver

Y101

CR-5

8.000 MHz Crystal

TR-4
TR-4E

Power Supply ; 115V AC
Power Supply ; 220V AC

6.13

Sample Programs
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180

REM ***DUMB TERMINAL PROGRAM FOR THE Serial488A
REM ***
Running under IBM Basica
REM ***
This Program allows direct interaction between the
REM ***
IBM-PC and an IEEE bus device through the Serial488A.
REM ***The Serial488A must be configured as the IEEE bus
REM ***
controller and have talk back on terminator enabled.
REM ***REM ***REM ***
CLS' Open the serial communications port and set the serial parameters
OPEN "COM1: 9600,n,8,2,cs,ds" AS 1
' Display any characters received from the COM1 port
IF LOC(1) THEN PRINT INPUT$(LOC(1),1);' Transmit any key presses from keyboard to the COM1 port and to the screen
K$=INKEY$
PRINT #1,K$; : PRINT K$;
GOTO 140 ' Do it again

A.1

Appendix B

Character Codes and IEEE Multiline Messages

0 $10

$00

NUL

16 $20

DLE

SOH
GTL
$02

DC1
LLO
2 $12

STX
ETX

DC3

EOT
SDC
$05

DC4
DCL
5 $15

ENQ
PPC
$06

BEL
BS
GET
$09

ETB

EM

VT

ESC

FF
CR
SO

-

RS

SI

US

ACG

UCG

.

N

?
UNL

LAG

ACG = Addressed Command GroupUCG = Universal Command GroupLAG = Listen Address Group

O
15

m

^

UNT

TAG

SCG
110 $7E

126~
SCG
111 $7FSCG
95 $6F

o
SCG

125

}

n

_

124

|
SCG
109 $7DSCG
94 $6E30
79 $5F14
63 $4F30
47 $3F

l

]

123

{
SCG
108 $7CSCG
93 $6D29
78 $5E13
62 $4ESCG
107 $7B

SCG
92 $6C28
77 $5D

122

z

k

\

M

>

/
15

L

=

j

[

121

y
SCG
106 $7A

SCG
91 $6B27
76 $5C12
61 $4D29
46 $3E14
31 $2F

K

<

i

Z

120

x
SCG
105 $79SCG
90 $6A26
75 $5B

11
60 $4C28
45 $3D13
30 $2E

15 $1F

$0F

,

GS

J

;

h

Y

119

w
SCG
104 $78SCG
89 $6925
74 $5A10
59 $4B27
44 $3C12
29 $2D

14 $1E

$0E

+

FS

I

:
26
43 $3B11
28 $2C

13 $1D

$0D

*

g

X

118

v
SCG
103 $77SCG
88 $6824
73 $5909
58 $4A25
42 $3A09
26 $2A

H

9

f

W
23
72 $580857 $4924
41 $3910
27 $2B

12 $1C

$0C

8

)

SUB
11 $1B

$0B

(

G

117

u
SCG
102 $76SCG
87 $6722
71 $5707
56 $48

e

V

116

t
SCG
101 $75SCG
86 $66

F

7

d

U
21
70 $5606
55 $4723
40 $380825 $29SPD
10 $1A

LF

'

CAN

HT

6
22
39 $3707
24 $28

SPE
9 $19

TCT
$0A

&

E

115

s
SCG
100 $74SCG
85 $6520
69 $5505
54 $46

c

T

114

r
SCG
99 $73SCG
84 $64

D

5

b

S
19
68 $5404
53 $4521
38 $3605
22 $2606
23 $27

8 $18

$08

%

SYN
7 $17

$07

4
20
37 $3504
21 $25

NAK
PPU
6 $16

ACK

$

C

113

q
SCG
98 $72SCG
83 $6318
67 $5303
52 $44

a

R

112

p
SCG
97 $71SCG
82 $62B

3
19
36 $34Q
17
66 $5202
51 $43

96 $70`SCG
81 $61

A

2#

80 $60P
16
65 $5101
50 $42

18
35 $3303
20 $24

4 $14

$04

1

"

64 $50@00
49 $41

17
34 $3201
18 $2202
19 $23

3 $13

$03

!

DC2

48 $400
16
33 $3100
17 $21

1 $11$01

32 $30

SP

127

DEL
SCG

SCG

TAG = Talk Address GroupSCG = Secondary Command Group

B.1