IOtech serial488a schematic

Serial488A, Serial488A/OEM, Serial488A/512K

User’s Manual

IOtech, Inc.

25971 Cannon Road

Cleveland, OH 44146

Phone: [phone]

Fax: [phone]

E-mail: [e-mail]

Internet: http://www.iotech.com

Serial488A, Serial488A/OEM,

Serial488/512K User’s Manual

p/n

SERIAL488/A-901, Rev 2.3

© 1998 by IOtech, Inc. — Printed in the United States of America

Warranty

Your IOtech warranty is as stated on the product warranty card. You may contact IOtech by
phone, fax machine, or e-mail in regard to warranty-related issues.
Phone: [phone], fax: [phone], email:

[e-mail]

Limitation of Liability

IOtech, Inc. cannot be held liable for any damages resulting from the use or misuse of this
product.

Copyright, Trademark, and Licensing Notic e

All IOtech documentation, software, and hardware are copyright with all rights reserved. No
part 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 their
respective 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 of
Conformity 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 the
recommendations in this manual. Using this equipment in ways other than described in this manual can
present 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 from
electrical shock under noted conditions.

This ESD caution symbol urges proper handling of equipment or components sensitive to damage from
electrostatic 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.

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.

As applicable, IOtech calibrates its

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 of
continuous improvement, IOtech welcomes your suggestions.

Introduction

1.1 Description

The

Serial488A, Serial488A/OEM

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 then
automatically performs the bus seq uences necessary to send this data to t he 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, 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

422 devices by positioning configuration jumpers located within the unit. Both
devices can communicate at selectable baud rates up to 57600 baud.

and

Serial488A/OEM

and

Serial488/512K

can communicate with RS-232 and RS-

Bus Converters

The

Serial488/512K

rates up to 19200 baud.

This manual will refer to all three interfaces as the
between the
applicable.

Serial488A, Serial488A/OEM

can communicate with RS-232 devices at selectable baud

. Differences

and

Serial488/512K

Serial488A

will be noted where

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

characters. The

allocated fixed serial and IEEE input buffers of 4000

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 been
changed to include status of the serial handshake. Other minor changes
have also been included. Refer to Section 4.4 for a complete description
of 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 to

the serial and IEEE input buffers as required.

2. The

RS-422 levels. The

3. The

Serial488A

Serial488/512K

Serial488A

up to 57600 baud. The

and

Serial488A/OEM

can only operate at RS-232 levels.

and

Serial488A/OEM

Serial488/512K

have the ability to output RS-232 or

can operate at selectable baud rates

can operate at selectable baud rates up to

19200 baud.

1.2

1.4 Available Accessories

Additional accessories that can be ordered for the

CA-7-1
CA-7-2
CA-7-3
CA-7-4
CA-11
CA-21
CA-22
CA-23
CN-20
CN-22
CN-23
ABC488
Rack488-3
Rack488-4
140-0920

Serial488A

include:

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 parallel
IEEE 488 panel mount feed-through connector, male and female
IEEE 488 ABC switch
5-1/4" by 19" rack mount for one
5-1/4" by 19" rack mount for two

Serial488A

Serial488A

s

Instruction Manual

1.3

Specifications

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!

If equipment is used in any manner not specified in this manual, the protection provided by the
equipment may be impaired. Please read this manual carefully.

Do not connect AC line power directly to the Serial488A. Direct AC connection will damage the
equipment.

Serial488A

:$51,1*

:$51,1*

&$87,21

IEEE 488

&$87,21

The 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: 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: Selectable CTS/RTS or XON/XOFF.
Terminators: Selectable CR, LF, LF-CR and CR-LF.
Connector: 25-pin Sub-D male. DCE Configured.

General

Terminal Installation Category:

Standard: Not Applicable

CE: Category 1 for all terminals.
Data Buffer: 32,000 characters dynamically allocated.
Indicators: LEDs for IEEE Talk and Listen, Serial Send and Receive, and

Power.

Power: An external power supply is provided with the Serial488A.

Input is 105 to 125VAC; 50 to 60 Hz, 10 VA Maximum.

Dimensions: 188mm deep x 140mm wide x 68mm high (7.39" x 5.5" x

2.68").

Weight: 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: 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: 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.
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: Selectable CTS/RTS or XON/XOFF.
Terminators: Selectable CR, LF, LF-CR and CR-LF.
Connector: 25-pin Sub-D male. DCE Configured.

General

Data Buffer: 32,000 characters dynamically allocated.
Indicators: LEDs for IEEE Talk and Listen, Serial Send and Receive, and

Power.
Power: User supplied +5 volts ±0.25% at 1 amp. Mating power

connector with 8 inch leads provided.
Dimensions: 205mm deep x 115mm wide x 28mm high (8" x 4.5" x 1.1").
Weight: 0.23kg. (0.5 lbs.)
Environment: 0° - 50°C; 0 to 70% R.H. to 35°C. Linearly derate

3% R.H./°C from 35° to 50°C.
Controls: 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: 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: AB, BA, BB, CA, CB
Character Set: Asynchronous bit serial.
Output Voltage: 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, and 19,200.
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: Selectable CTS/RTS or XON/XOFF.
Terminators: Selectable CR, LF, LF-CR and CR-LF.
Connector: 25-pin Sub-D male. DCE Configured.

General

Data Buffer: 512,000 characters.
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.
Dimensions: 188mm deep x 140mm wide x 68mm high (7.39" x 5.5" x

2.68").
Weight: 1.95 kg. (4.35 lbs).
Environment: 0° - 50°C; 0 to 70% R.H. to 35°C. Linearly derate

3% R.H./°C from 35° to 50°C.

Controls: Power Sw itch (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 IEEE bus address "n"

ATN Attention line
CA Controller Active
CO Controller
CR Carriage Return
data Data String
DCL Device Clear
GET Group Execute Trigger
GTL Go To Local
LA Listener Active
LAG Listen Address Group
LF Line Feed
LLO Local Lock Out
MLA My Listen Address
MTA My Talk Address
PE Peripheral
PPC Parallel Poll Configure
PPU Parallel Poll Unconfigure
SC System Controller
SDC Selected Device Clear
SPD Serial Poll Disable
SPE Serial Poll Enable
SRQ Service Request
TA Talker Active
TAD Talker Address
TCT Take Control
term Terminator
UNL Unlisten
UNT Untalk
* Unasserted

1.8

Getting Started

2.1 Inspection

The

Serial488A

prior to shipment. When you receive the interface, carefully unpack all items from the
shipping carton and check for any obvious signs of physical damage which may have
occurred 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

Every

Serial488A

•

Serial488A

•

140-0920

•

Power Supply

Serial488A/OEM

was carefully inspected, both mechanically and electrically,

is shipped with the following....

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

is shipped with the following....

Every

•

Serial488A/OEM

•

140-0920

Serial488/512K

•

Serial488/512K

•

140-0920

•

Power Supply

IEEE 488 Bus Converter
Instruction Manual

is shipped with the following....

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 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 settings which are:

Serial Port: IEEE:

9600 Baud Mode = IEEE 488 Controller
8 Data Bits Address = 10
2 Stop Bits Bus Terminator = LF; EOI Disabled
No Parity Talk-back on Terminator Enabled
Serial Terminator = LF Talk-back on Time Out Enabled
Echo Disabled
RTS/CTS Handshake

SW3 Factory Default Settings

IEEE Addr

IEEE Term

EOI

12345678

SW3

OPEN

10
LF
Disabled

Switch

DOT

Side
View

2.2

SW2 Factory Default Settings

Mode

Talk Back on Time Out

Serial Term

Echo

Parity

Handshake

Word Length

Talk Back on Term

12345678

SW2

OPEN

C

Enabled

LF
No Echo
No Parity

SW1 Factory Default Settings

12345678

Baud Rate

Stop Bits

SW1

9600
RTS/CTS
8 Data Bits
Enabled
2 Stop Bits

OPEN

Switch

DOT

Side
View

DOT

Switch

Side
View

The following drawings show the locations of switches SW1, SW2, and SW3 for

the

Serial488A, Serial488A/OEM

the

Serial488A

and the

Serial488/512K

and the

Serial488/512K

is referred to as the I/O board.

2.3

. The top circuit board in

Serial488A Switch Location - I/O Board

12345678

OPEN

12345678

OPEN

12345678

S203

SW2 SW3

S202

SW3

SW2

SW1

OPEN

S201

Serial488A/OEM Switch Location

S101

12345678

SW1

OPEN

SW-6-8

S102

12345678

SW2

OPEN

SW-6-8

S103

12345678

SW3

SW1

OPEN

SW-6-8

2.4

Serial488/512K SW1, SW2 Location - I/O Board

12345678

SW2

SW-6-8

12345678

OPEN

IC-39

74HCT244

C-5-.1

RN-1-10K

SW1

OPEN

SW-6-8

Serial488/512K SW3 Location - Motherboard

12345678

OPEN

SW3

S102

2.5

Note that the

the

Serial488A

Serial488A

is designed to allow an RS-232 computer to communicate with an

comes configured as an IEEE controller. In t his mod e

IEEE peripheral such as a plotter. This controller mode is described in detail in

Section 3

.

The

Serial488A

peripheral, the

Serial488A

device. The peripheral mode of operation is described in detail in

may also be configured as an IEEE peripheral. As an IEEE

allows an IEEE controller to commun icate with an RS-232

Section 4

.

To modify any of these defaults, follow this simple procedure: Disconnect the
power 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 is
connected to the AC line. Failure to observe this
warning 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 your
installation and then carefully re-assemble the interface using the reverse of the
procedure 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 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 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

,

12345678

110 1800

OPEN

12345678

110 2400

OPEN

12345678

110 3600

OPEN

12345678

135 4800

OPEN

12345678

150 7200

OPEN

12345678

12345678

OPEN

12345678

OPEN

12345678

OPEN

12345678

OPEN

12345678

OPEN

12345678

Switch

Side
View

DOT

300 9600

OPEN

12345678

600 19200

OPEN

12345678

1200 57600

OPEN

OPEN

12345678

OPEN

12345678

OPEN

2.7

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

12345678

OPEN

12345678

OPEN

Switch

Side
View

DOT

8 Data Bits 7 Data Bits

2.3.3 Serial Stop Bit Selection

Switch SW1-8 determines the number of stop bits contained in each
serial character transmitted and received. The factory default is 2 stop bits.

SW1 View for Serial Stop Bit Selection

12345678

OPEN

12345678

1 Stop Bit 2 Stop Bits

Switch

Side
View

OPEN

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 not
check parity on data that is received. The factory default is parity disabled.

2.8

SW2 View for Serial Parity Selection

12345678

OPEN

Odd Parity Mark Parity

12345678

OPEN

Even Parity Space Parity

12345678

Parity Disabled

2.3.5 Serial Echo Selection

12345678

OPEN

12345678

OPEN

OPEN

Switch

DOT

Side
View

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.

12345678

OPEN

Echo Disabled Echo Enabled

SW2 View for Echo Selection

12345678

OPEN

Switch

DOT

Side
View

2.9

2.3.6 Serial Handshake Selection

Switch SW1-5 is used to select between hardware [
software [

With

Xon/Xoff

Xon/Xoff

] serial handshake control.

, the

Serial488A

issues an

Xoff

RTS/CTS

character [ASCII value

] or

of $13] when its buffer memory is near full. When issued, there is greater
than 1000 character locations remaining to protect against buffer overrun.
When it is able to accept more information it issues an
[ASCII value of $11]. The

Serial488A

from the serial host it is communicating with.
becomes inactive when

Xon/Xoff

set to an active high state. The

is enabled. The

CTS

also accepts

Xon/Xoff

RTS/CTS

output is, however,

RTS

input is not used for this handshake

Xon

serial control

character

on transmit

and may be left floating (unconnected).

With

RTS/CTS

, the

Serial488A

un-asserts

(low) when its buffer

RTS

memory is near full. When un-asserted, there is greater than 1000 character
locations remaining to protect against buffer overrun. When it is able to
accept more information it asserts (high)
transmit data to the serial host if it detects the

RTS

CTS

. The

Serial488A

will not

input un-asserted (low)

when configured for this hardware handshake.

The factory default serial control is hardware,

SW1 View for Serial Handshake Selection

12345678

OPEN

RTS/CTS Xon/Xoff

12345678

OPEN

RTS/CTS

Switch

Side
View

.

DOT

2.10

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 is
discarded and substituted with an IEEE CR-LF. 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

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 and

output. The factory default is LF Only.

SW2 View for Serial Terminator Selection

12345678

OPEN

CR Only LF-CR

12345678

OPEN

LF Only CR-LF

12345678

OPEN

12345678

OPEN

Switch

DOT

Side
View

2.11

2.4.2 IEEE Bus Terminator Selection

SW3-6 through SW3-8 set the IEEE bus terminators used for data sent

or received by the

Serial488A

. 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.

SW3 View for IEEE Bus Terminator Selection

12345678

12345678

12345678

EOI Disabled EOI Enabled

2.5 Mode Selection

12345678

OPEN

OPEN

CR Only LF-CR

12345678

OPEN

OPEN

LF Only CR-LF

12345678

OPEN

OPEN

Switch

DOT

Side
View

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

controller. Data whi ch is sent b y the IEEE control ler to t he

mode is used when interfacing a serial device to an IEEE

Serial488A

is transmitted
out its serial port. Data received from the serial device is buffered by the
until read by the IEEE controller. Refer to

Section 4

for more detailed information on

the peripheral mode of operation.

Serial488A

The factory default is the

IEEE Controller

mode, an RS-232 to IEEE converter.

SW2 View for Mode Selection

12345678

OPEN

Controller Mode Peripheral Mode

12345678

OPEN

Switch

Side
View

DOT

2.6 IEEE Address Selection

SW3-1 through SW3-5 select the IEEE bus address of the

the

IEEE Peripheral

mode. These same switches are used in the

Serial488A

IEEE Controller

mode to select the address of the device that will be controlled. [Refer to

when in

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 most
significant. The factory default is address 10.

Listen Only

the

Serial488A

is a special type of

Peripheral

accepts all data transmitted on the bus, ignoring any bus addressing,

and transfers it out its serial port. The

Serial488A

operation. In the

is set to

Listen Only

Listen Only

mode by

mode

setting its ad dress to 31. If the IEEE address is set to 31 in the pe ripheral mode, it is
adjusted to 30.

2.13

SW3 View for IEEE Address Selection

12345678

0
1

OPEN

0 x 16
1 x 8
0 x 4
1 x 2
0 x 1

+

Switch

Side
View

= 0
= 8
= 0
= 2
= 0

DOT

IEEE 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 IEEE
bus terminators, address the attached bus device to talk. The factory default
is

Talk-back On Terminator

SW2-2 selects whether the
bus device to talk when the
device. The factory default is

Refer to

Section 3

for complete details on these features.

enabled.

Serial488A

Serial488A

should address the attached

has nothing more to send to that

Talk-back On Time Out

enabled.

2.14

SW1 View for Controller Talk-Back on Terminator Selection

12345678

OPEN

Talk Back on

Terminator Disabled

SW2 View for Controller Talk-Back on Time-Out Selection

12345678

OPEN

Talk Back on

Time Out Disabled

2.7.2 Peripheral Features

12345678

OPEN

Talk Back on

Terminator Enabled

12345678

OPEN

Talk Back on

Time Out Enabled

Switch

DOT

Side
View

DOT

Switch

Side
View

In the

IEEE Peripheral

enables the interface to assert the

(IEEE 488 to RS-232 converter) mode, SW1-7

IEEE bus interface line to indicate

SRQ

that it has received the last switch selected serial terminator character from
the serial device.

SW1 View for Peripheral SRQ on Last Serial Terminator

12345678

OPEN

SRQ on Last

Terminator Disabled

12345678

OPEN

SRQ on Last

Terminator Enabled

Switch

Side
View

DOT

2.15

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.

RS-232 Signal Levels Selected - Serial488A

Shorting Plug

J205

RS-422 RS-232

J206

2.16

RS-232 Signal Levels Selected - Serial488A/OEM

J106

RS-232

J105

RS-422

Shorting Plug

2.8.2 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

communications, which means the

's connector is configured as DCE type equipment for RS-232

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

Serial488/512K

does not support RS-422 communication, the pins labeled

Serial488A

. Note: since the

+TxD and +RxD are not used. Any reference to RS-422 communication
does not apply to the

Serial488/512K

.

2.17

Rear View of the Serial488A's Serial Connector

+VTEST

GND

13

25

-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

RTS

+VTEST

+TXD

-RXD

-TXD

+RXD

1

14

CTS Clear To Send - Input - Pin 4

The

Serial488A

input is used as a hardware handshake line to prevent the

CTS

from transmitting serial data when the RS-232 host is
not ready to accept it. When
the internal switches, the

while this line is un-asserted (low). If the RS-232 host is not

TxD

Serial488A

capable of driving this line it can be connected to the
(Pin 6) of the

line is not tested to determine if it can transmit data.

CTS

Serial488A

. If

2.18

RTS/CTS

will not transmit data out

Xon/Xoff

handshake is selected on

Vtest

output

handshake is selected, the

-

RTS Request To Send - Output - Pin 5

The

output is used as a hardware handshake line to prevent

RTS

the RS-232/RS-422 host from transmitting serial data if the

Serial488A

is not ready to accept it. When
is selected on the internal switches, the

output high when there are greater than 1000 character

RTS

locations available in its internal buffer. If the number of available
locations drops to less than 1000, the
(low) this output. If

Xon/Xoff

handshake is selected, the

will be permanently driven active high.

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.

RTS/CTS

Serial488A

Serial488A

handshake

will drive the

will un-assert

line

RTS

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° 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° 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
CTS

-TxD
Gnd

-RxD

+TxD
+RxD

6
7
5
3
9

4 14 +Rxd
8 16 +Txd

4

CTS

5

RTS

2

-RxD

7

Gnd

3

-Txd

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

Macintosh II/SE/Plus to Serial488A

Mini DIN8 Male DB-25 Male

RTS
CTS

-TxD

1
2
3

4

CTS

5

RTS

2

-RxD

Gnd

-RxD

+TxD
+RxD

4
5

6 14 +Rxd
8 16 +Txd

2.20

7

Gnd

3

-Txd

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

IBM PC/XT/PS2 to Serial488A

DB-25 Female DB-25 Male

-TxD

-RxD
RTS
CTS
DSR

Gnd

2
3
4
5
6

2
3
4
5
6

-RxD

-TxD
CTS
RTS
Vtest

7 7 Gnd

IBM AT to Serial488A Wiring Diagram (RS-232)

IBM AT to Serial488A

DB-9 Female DB-25 Male

DCD

-RxD

-TxD
DTR

1
2
3

3

-TxD

2

-RxD

4

Gnd
DSR
RTS
CTS

5

7

Gnd
6
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 and
reassembling 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 is
intended for INDOOR USE ONLY. Failure to
observe 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 the
self 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 off off on off on

No Error--Listen Only off on on off on
No Power off off off off off
Program Rom on on on on on
Ram - U209 blink off off off on

Ram - U210 blink off on off on
Ram - U211 blink off off on on
Ram - U212 blink off on on on

Ram - U213 blink on off off on
Ram - U214 blink on on off on
Ram - U215 blink on off on on
Ram - U216 blink on on on on

Ram - U208 off off off blink on
Ram - U201 off off on blink on
Ram - U202 off on off blink on
Ram - U203 off on on blink on

Ram - U204 on off off blink on
Ram - U205 on off on blink on
Ram - U206 on on off blink on
Ram - U207 on on on blink on

Logic Error blink blink blink blink on

2.23

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 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

for connecting IEEE bus instruments, the

[ 25-Pin Sub-D ]. Connect the other end to the host's serial port. Except

Serial488A

is installed and ready to use.

WARNING

The Serial488A makes its earth ground
connection 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

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
input data. When received, it addresses the selected IEEE device to listen with the
following bus sequence:

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
send data from it to the IEEE bus device. If the serial input buffer becomes emptied,
the

Serial488A

features is enabled. This allows the
devices, such as plotters or instruments, that return status and other information to the
host computer.

Serial488A

will command the IEEE bus device to talk if one of the talk back

mode allows a serial RS-232 or RS-422 host device to

has initialized itself after power-on, it waits for serial

ATN•UNL,MTA,LAG,*ATN

will continue to

Serial488A

Serial488A

to be used as a controller with

When the
bus sequence:

The

Serial488A

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.

Serial488A

then accepts data from the IEEE device an d ret u rn s i t to t h e ho s t

addresses the IEEE bus d ev ice t o t alk i t us es t he fo l l owi ng

ATN•UNL,MLA,TAG,*ATN

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 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 previous example, the serial terminator should be selected for CR Only
while the IEEE terminato r is set for CR-LF. When a s erial 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

Serial488A

can be made totally data transparent by setting both the serial
and IEEE terminators t o be CR Only or LF Only. Refer to Section 2 fo r the proper
switch 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

device that will be controlled, not the address of the

Serial488A

will be communicating with. These switches set the address of the IEEE

Serial488A

. The address of the

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 Selection

12345678

0
1

OPEN

0 x 16
1 x 8
0 x 4
1 x 2
0 x 1

+

Switch

Side
View

= 0
= 8
= 0
= 2
= 0

DOT

IEEE 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 the
attached bus device to talk after sending the selected IEEE bus
terminator(s). This feature is commonly used to provide bi-directional
communication wit h a si ngl e IEEE ins trumen t. Talk back will on ly occu r i f
there is no serial dat a to output to the IEEE device. The fact ory default is

Talk-back On Terminator

enabled.

SW1 View for Talk-Back on Terminator Selection

12345678

OPEN

Talk Back on

Terminator Disabled

12345678

OPEN

Talk Back on

Terminator Enabled

Switch

Side
View

DOT

3.3

When the serial input buffer becomes empty, the

Serial488A

checks
the last characters sen t to the IEEE b us device. If th ese were the IEEE bus
terminators and

Talk-Back on Terminator

device is addressed to talk. Any data received by the

is enabled, the IEEE bus

Serial488A

from the

bus device is sent to the serial host.

When the last IEEE bus t erminator is detected from the IEEE d evice,

the

Serial488A

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 following is an example of 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 Serial488A with
25 ' the Talk Back on Terminator Feature Enabled to
30 ' Communicate with a Keithley Model 196 DMM
40 '
50 ' Open Basic's serial communications port
60 OPEN "COM1: 9600,N,8,2" AS 1
70 ' Set the Model 196 DMM to the 30VDC range
80 PRINT #1,"F0R3X"; ' The ; suppresses terminators
90 ' Request 10 Readings from 196"
100 FOR N = 1 to 10
110 PRINT #1,"" ' Output terminator
120 LINE INPUT #1, A$ ' Get Reading from 196
130 PRINT A$ ' print it on the screen
140 NEXT N
150 END

3.4

3.4.2 Talk Back On Time Out

SW2-2 selects whether the
bus device to talk when the

Serial488A

Serial488A

should address the attached

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

12345678

OPEN

Talk Back on

Time Out Disabled

If

Talk-Back on Time-Out

12345678

OPEN

Talk Back on

Time Out Enabled

is enabled, then

Switch

Side
View

Serial488A

DOT

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, 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 Time-Out

feature should be

enabled.

When the last IEEE bus t erminator is detected from the IEEE d evice,

the

Serial488A

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.

3.5

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 Serial488A
20 ' This Program allows direct interaction
between
30 ' 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$(LOC(1),1);: GOTO 90
100 ' Transmit key presses to the COM1 port and
screen
110 K$=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

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 the

Serial488

'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 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

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 or
compatible. Because PC and compatibles output RS-232 levels, the shorting DIP
jumper should be set to the RS-232 position (J206).

Selecting RS-232 Signal Levels - Serial488A

Shorting Plug

J205

RS-422 RS-232

J206

3.8

Selecting RS-232 Signal Levels - Serial488A/OEM

J106

RS-232

RS-422

Shorting Plug

J105

3.9

Serial488A Settings For Use With HP 7580A Plotter on an IBM PC

SW3

EOI

5
CR Only
Enabled

IEEE Addr

IEEE Term

Mode

Talk Back on Time Out

Serial Term

Echo

Parity

12345678

OPEN

12345678

SW2

OPEN

C

Enabled

CR
No Echo
Even

Switch

DOT

Side
View

DOT

Switch

Side
View

Baud Rate

Handshake

Word Length

Talk Back on Terminator

Stop Bits

12345678

SW1

OPEN

9600

Xon/Xoff

7 Data Bits
Enabled
1 Stop Bit

Switch

DOT

Side
View

3.10

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 which
allows selection of baud rate, stop bits and parity. With this driver, the word length is
fixed to 7 data bits with Xon/Xoff 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.

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

Shorting Plug

J205

RS-422 RS-232

J206

3.12

Selecting RS-422 Signal Levels - Serial488A/OEM

J106

RS-232

J105

RS-422

Shorting Plug

3.13

The following illustrates the

Serial488A

's internal switch settings for use with

MacPlot utilizing the previously described format.

Serial488A Settings For Use With HP 7580A Plotter on a Macintosh

SW3

EOI

5
CR
Enabled

IEEE Addr

IEEE Term

Mode

Talk Back on Time Out

Serial Term

Echo

Parity

12345678

OPEN

12345678

SW2

OPEN

C

Enabled

CR
No Echo
No Parity

Switch

DOT

Side
View

DOT

Switch

Side
View

Baud Rate

Handshake

Word Length

Talk Back on Terminator

Stop Bits

12345678

SW1

OPEN

57600

Xon/Xoff

7 Data Bits
Enabled
1 Stop Bit

3.14

Switch

DOT

Side
View

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 Powe r 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 the
serial data format, word length, stop bits and parity.

3.6 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
them. The

Serial488

does not use secondary commands to control IEEE peripherals,

Serial488A

to control

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 i nstrument, to an IEEE contro ller. Data which is sent b y the IEEE
controller to the
received from the serial device is buffered by the
controller. The
32,000 bytes of data from both the IEEE input and the serial input. The

Serial488/512K

serial input.

Serial488A

Serial488A

can buffer 512,000 bytes of data from both the IEEE input and the

is buffered and transmitted out its serial port. Data

until read by the IEEE

can buffer approximately

and the

Serial488A

Serial488A/OEM

The

Serial488A

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 (
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
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 when, and where, required.

).

will refuse to accept more data from the IEEE controller when

Serial488A

) output or by transmitting the

RTS

is dynamically allocated for the serial input and

Xoff

ASCII

There are approximately 250 available queues in the

Serial488A/OEM

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.

for a total of 32,000 bytes of buffer (character) space. Queues are

4.1

Serial488A

and the

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 is
accomplished 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 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

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 for
data space in the buffer to become available, the data can simply be sent to
the

Serial488A

controller is blind as to whether or not the

. This is referred to as blind data transfers because the IEEE

Serial488A

is capable of
accepting data. In this case, the bus controller's output data transfer will be
held 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 of
control might be appropriate in a single user environment.

To illustrate how this would appear, let's assume the

Serial488A

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

Serial488A

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

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 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

Serial488A

, the bus will hang until serial data is received.
If no serial data is received it will hang forever or until the controller times
out.

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 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

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 the
serial 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 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.

4.3

When serial data is received, DIO5 of the Serial Poll byte is set, '1', to
indicate 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 is
read by the IEEE controller this bit is reset.

The

Serial488A

receives the last serial terminator. To enable this feature, the

switch, located on the internal switch bank of SW1, must be enabled.

SRQ

When enabled, the

can generate a request for service on the bus when it

Peripheral

Serial488A

will assert the IEEE b us

line and set

SRQ

serial poll status bits DIO7 and DIO3 when the last serial terminator is
detected. The IEEE controller must perform a serial poll on t he interface to
clear 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
service request (

SRQ

).

Serial488A

will not generate a

SW1 View For Selecting SRQ on Last Terminator

12345678

OPEN

SRQ on Last

Terminator Disabled

12345678

OPEN

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

.

DIO8 IEEE Input Buffer NOT Empty

This bit is set when the IEEE input buffer contains one or more
data bytes which have not been sent out the serial port. It is
cleared, set to "0", when the buffer is empty.

4.4

Serial Poll Status Byte

1428163264128

DIO8 DIO7 DIO6 DIO5 DIO4 DIO3 DIO2 DIO1

ce - rsv bit

ffer Not Empt y

Serial Handsh ake

Not Used - Al ways '0'

Request Servi

IEEE Input Bu

Serial Input Buffer Not Em pty

IEEE Input Bu ffer Full

DIO7 rsv

This bit is defined by the IEEE 488 Specification and is used to
indicate to the bus controller that the
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 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.

Last Serial I nput Terminat or

Serial488A

Not Used - Al ways '0'

is the bus device

4.5

DIO4 IEEE Input Buffer Full

When this bit is set, it indicates that the
the controller on subsequent data transfers. The interface may
continue to accept an additional 512 characters but this is
dependent on the serial input buffer size.

DIO3 Received Last Serial Terminator

This bit is set [1] when the

Serial488A

terminator at its serial input. It remains set as long as there is at
least one serial terminator in the serial input buffer. If the

Peripheral SRQ

feature is enabled, the
request for service by asserting the
bit [DIO7]. The

bit is cleared, along with the

rsv

serial polled by the controller. If there are additional serial
terminators in the serial input buffer,

SRQ

line and

bit when the last IEEE 488 bus terminator is sent

rsv

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
of 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.

Serial488A

detects the last serial

Serial488A

line and also set the

SRQ

SRQ

Serial488A

will reassert the

Serial488A

may hold off

will issue a

rsv

line, when

is capable

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 retu rn [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 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

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
should refer to

Section 2

of this manual.

Serial488A

's serial and bus terminators you

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 and
multiline commands that the

Remote Enable
Go to Local
Group Execute Trigger
Local Lockout
Take Control
Parallel Poll
Parallel Poll Configure
Parallel Poll Unconfigure
Parallel Poll Disable

Serial488A

does not support or respond to include:

(REN)

(GTL)

(GET)

(LLO)

(TCT)

(PP)

(PPC)

(PPU)

(PPD)

4.6.1 My Talk Address

When the

Serial488A

(MTA)

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

Serial488A

will continue to output serial input buffer data as long as the

IEEE controller allows.

4.6.2 My Listen Address

(MLA)

4.7

When the

Serial488A

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.

4.6.3 Device Clear

Device Clear resets the

buffers. Any pending data and Service Requests (

(DCL and SDC)

Serial488A

's IEEE input and serial input

), including the

SRQ

information they convey, are lost.

4.6.4 Interface Clear

IFC places the

(IFC)

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

When Serial Poll Enabled, the

(SPE)

Serial488A

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
cleared. The

Serial488A

will continue to try to output its serial poll

SRQ

s are

response until it is 'Serial Poll Disabled' by the controller.

4.6.6 Serial Poll Disable

Disables the

Serial488A

controller.

(SPD)

from responding to serial polls by the

4.8

4.6.7 Unlisten

(UNL)

UNL places the

4.6.8 Untalk

UNT places the

Serial488A

(UNT)

Serial488A

in the Listener Idle State.

in the Talker Idle State.

4.7 IEEE Address Selection

SW3-1 through SW3-5 select the IEEE bus address of the

the

IEEE Peripheral

Serial488A

mode. The address is selected by simple binary weighting with

when in

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 Selection

12345678

0
1

OPEN

Switch

Side
View

DOT

0 x 16
1 x 8
0 x 4
1 x 2
0 x 1

IEEE Address = 10

= 0
= 8
= 0
= 2
= 0

+

4.7.1 Listen Only Mode

Listen Only

Only

mode the

is a special type of

Serial488A

accepts all data transmitted on the bus and

transfers it out its serial port. The

Peripheral

Serial488A

operation. In the

is set to

Listen Only

by setting its address to 31 (switches SW3-1 through SW3-5 all open).

Listen

mode

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 direct
interaction from the keyboard.

In this program example, key p resses are detected and sent via th e IEEE bus to

the

Serial488A

characters are buffered by the

. The character is then sent to the serial device. Any incomming serial

Serial488A

. The

Serial488A

is polled by the controller
for any data in the serial input buffer. When data is detected, it is read by the
controller one charact er at a time and print ed on the PC's s creen. The IEEE addr ess 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$(1,1) : PRINT
S$;
160 GOTO 120 ' Try for more

4.10

IEEE 488 Primer

5.1 HISTORY

The

IEEE 488

Institute of Electrical and Electronic Engineers in 1975 and revised in 1978. The

Serial488A

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 and
software interfaces. The popularity of the

eneral Purpose Interface Bus or

G

electrical and mechanical interface as well as the data transfer and control protocols.
The use of the
design of the interface to design of the high level software that is specific to the
measurement application.

5.2 GENERAL STRUCTURE

The main purpose of the
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
on, the

conforms to this most recent revision designated

Active Controller

bus is an instrumentation communication bus adopted by the

IEEE 488-1978

interface (sometimes called the

which is, at power

IEEE 488

.

IEEE 488

GPIB

standard has moved the responsibility of the user from

GPIB

is to transfer information between two or more

) is due to the total specification of the

System Controller

.

The

System Controller

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
which is recognized to speak is the
time if the information transferred is to be clearly understood by all. The act of "giving
the floor" to that device is called
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
the

Active Controller

At a committee meeting, everyone present usually listens. This is not the case
with the

GPIB

. The

.

Active Controller

is similar to a committee chairman. On a well run

Active Talker

Addressing to Talk

selects which devices will listen and

5.1

. There can only be one Talker at a

. If the committee chairman can

GPIB

, this device becomes

commands all other devices to ignore what is being transmitted. A device is instructed
to listen by being

Listener

. Devices which are to ignore the data message are instructed to

Addressed to Listen

. This device is then referred to as an

Unlisten

Active

.

The reason some devices are instructed to

Unlisten

is quite simple. Suppose a
college instructor is presenting the day's lesson. Each student is told to raise their
hand 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

called

handshaking

For data transfer on the
a)

Unlisten

b) Designate who will
c) Designate all the devices who are to

devices to

transfers information in a similar way. This method of data transfer is

. More on this later.

IEEE 488

, the

Active Controller

must…

all devices to protect against eavesdroppers.

listen

by

talk

addressing

.

a device to

listen

by

.

talk

addressing

those

d) Indicate to all devices that the data transfer can take place.

5.2

Device 1

System Controller

Able to Talk,

Listen, and Control

Device 2

DMM

Able to Talk

and Listen

Device 3

Printer

Only Able to Listen

To Other Devices

Data Bus

Data Byte
Transfer
Control

General
Interface
Management

Device 4

Frequency Counter

Only Able to Talk

IEEE 488 Bus Structure

Figure 5.1

5.3

DIO1-8

}

DAV
NRFD
NDAC

IFC
ATN
SRQ
REN
EOI

5.3 SEND IT TO MY ADDRESS

In the previous discussion, the terms

Listen

were used. These terms require some clarification.

The

IEEE 488

standard permits up to 15 devices to be configured within one

Addressed to Talk

and

Addressed to

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 product'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

Controller
Address

. These commands include

(MTA),

Talk Address Group

universal (multiline

My Listen Address

(TAG), and

) commands from the

(MLA),

Listen Address Group

Active

My Talk

(LAG).

5.4 BUS MANAGEMENT LINES

Five hardware lines on the

lines are often referred to as

GPIB

uniline

are used for bus management. Signals on these

(single line) commands. The signals are active
low, i.e. a low voltage represents a logic "1" (asserted), and a high voltage represents a
logic "0" (unasserted).

5.4.1 Attention (ATN)

is one of the most important lines for bus management. If

ATN

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 Listener

s. The

Active Controller

is the

only bus device that has control of this line.

5.4

5.4.2 Interface Clear (IFC)

The

line is used only by the

IFC

System Controller

. It is used to place

all bus devices in a known state. Although device configurations vary, the

command usually places the devices in the Talk and Listen Idle states

IFC

(neither

Active Talker

nor

Active Listener

).

5.4.3 Remote Enable (REN)

When the

System Controller

will respond to remote operation. Generally, the
issued before any bus programming is attempted. Only the

Controller

has control of the

Remote Enable

sends the

REN

line.

command, bus devices

command should be

REN

System

5.4.4 End or Identify (EOI)

The
The device that is sending the data asserts
data byte. The

line is used to signal the last byte of a multibyte data transfer.

EOI

during the transfer of the last

EOI

signal is not always necessary as the end of the data may

EOI

be indicated by some special character such as carriage return.

The

Active Controller

simultaneously asserting

also uses

and

EOI

ATN

to perform a

EOI

.

5.4.5 Service Request (SRQ)

When a device desires the immediate attention of the
it asserts

. It is then the Controller's responsibility to determine which

SRQ

device requested service. This is accomplished with a

Parallel Poll

.

Parallel Poll

by

Active Controller

Serial Poll

or a

5.5

5.5 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.

5.5.1 Data Valid (DAV)

The

DAV

NDAC

is asserted (active low) which indicates that all Listeners have
accepted the previous data byte transferred. The
the bus and waits until
Addressed Listeners are ready to accept the information. When

NDAC

are in the proper state, the

line is controlled by the

NRFD

is unasserted (high) which indicates that all

Talker

Talker

asserts

. The

Talker

DAV

Talker

verifies that

then outputs data on

NRFD

and

( active low) to

indicate that the data on the bus is valid.

5.5.2 Not Ready for Data (NRFD)

This line is used by the

Listeners

ready to accept new data. The

to inform the

Talker

must wait for each

Talker

when they are

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.

5.5.3 Not Data Accepted (NDAC)

The

NDAC

to the

Talker

information. Each device releases

NDAC

will not go high until the slowest Listener has accepted the data byte.

line is also controlled by the

Listeners

. This line indicates

that each device addressed to listen has accepted the

NDAC

(high) at its own rate, but the

5.6

DIO1-8

(composite)

1st Data Byte 2nd Data Byte

DAV

Source

NRFD

Acceptor

NDAC

Acceptor

Ready

Accept

Valid Not

All

None

None

Ready

Accept

All

Valid

All

Ready

None

Accept

Valid

Not

Valid

None

Ready

All

Accept

IEEE Bus Handshaking

5.6 DATA LINES

The

GPIB

These eight data lines use the convention of

provides eight data lines for a bit parallel/byte serial data transfer.

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

(bus) commands are sent by the

asserted. These commands include addressing commands for talk, listen,

with

Multiline
ATN

Untalk and Unlisten.

5.7.1 Go To Local (GTL)

This command allows the selected devices to be manually controlled.

($01)

Active Controller

over the data bus

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 least
significant bits are the address of the device being told to listen.

5.7.3 Unlisten (UNL)

This command tells all bus devices to Unlisten. The same as
Unaddressed to Listen. ($3F)

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 least
significant 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

command prevents manual control of the instrument's

LLO

functions. ($11)

5.7.7 Device Clear (DCL)

This command causes all bus devices to be initialized to a pre-defined
or 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

command disables all devices from sending their Serial Poll

SPD

status byte. ($19)

5.7.10 Serial Poll Enable (SPE)

A device which is Addressed to Talk will output its Serial Poll status
byte after

is sent and

SPE

is unasserted. ($18)

ATN

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
which data bit they are to assert in response to a

Parallel Poll

Parallel Poll

. ($05)

as to

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 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,

is very important to the test system

SRQ

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

. A DMM might

SRQ

assert it when its measurement is complete, if its input is overloaded or for any of an
assortment of reasons. A power supply might
This is a powerful bus feature that removes the burden from the
to periodically inquire, "Are you done yet?". Instead, the

if its output has current limited.

SRQ

System Controller

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

is a single line command, there is no way for the

SRQ

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

.

5.10

5.8.1 Serial Poll

Suppose the

Controller

let's assume there are several devices which could assert

Controller

issues an

SPE

receives a service request. For this example,

. The

SRQ

(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

bits will indicate why the device wanted service. This

. Often times the other

SRQ

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 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

Controller
Controller

(under user's software) conducts a
must then analyze the eight bits of data received to determine

the source of the request. Once the source is determined, a

is asserted, the

SRQ

Parallel Poll

Serial Poll

. The

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

5.11

Serial Poll

only.

Service Information

6.1 Factory Service

f problems are encountered in using the

I

the factory. Many problems can be resolved by discussing the problems with our
applications 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
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.

Serial488A

is a 6809 microprocessor [U101] supported by 8K

Serial488A

you should first telephone

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 Device Part Number Function

$0000-$7FFF U103 58258 Static RAM
$A000-$A007 U106 9914A IEEE Controller
$A800-$A807 U105 6551 UART
$B000-$B00F U104 65B22 VIA
$B800 U201 74HCT244 SW1 (S201)
$B801 U202 74HCT244 SW2 (S202)
$B802 U203 74HCT244 SW3 (S203)
$E000-$FFFF U102 2764 Programmed EPROM

6.2

6.3 Serial488A Mother Board Component Layout

C118

Y101

C104

D101

U104

U105

R101

C103

C102

C117

U103

U102

D102

D106

C105

C110

J104

D105

C113

U110

U113

D104

D103

R104

C101

C106

C107

U106

U101

U107

R102

C108

U108

C124

+

+

J101

6.3

6.4 Serial488A I/O Board Component Layout

CN-11

BLK

RED

R205

P204

U201

C201

R201

12345678

SW-201

OPEN

OPEN

C205

U205

C210

U206

C206

U202

SW-202

U203

C202

R202

12345678

SW-203

OPEN

C212

C203

R203

12345678

+

C211

+ +

U209

C213

+

C214

R206

J205

J206

C207

U208U207

R207

S205

C208

J204

14

1

J203

CN-8-25

J202

S201

S202

S203

SW1 SW2 SW3

6.4

C209

CA-19-8

13

25

6.5 Replaceable Parts List - Serial488A

Schematic Part Number Description

C101-C108 C-5-.1 Ceramic, 25v
C110,C113 C-5-.1 Ceramic, 25v
C117,C118 C-5-15p Ceramic, 25v
C124 C-2-10 Electrolytic, 25v
C211-C214 C-2-10 Electrolytic - 25v
C201-C203 C-5-.1 Ceramic, 25v
C205-C209 C-5-.1 Ceramic, 25v
C210 C-5-1 Ceramic, 25v
D101 RF-1 Small Signal Diode
D102-D106 DD-2 Red PC Mount
J101 CN-2 IEEE 488 Connector
J104 CN-5-13 13 x 2 0.1" Header
J201 CN-11 9 Volt Power Jack
J204 CN-8-25 PC Mount Female DB-25
J205 CA-19-8 8 Pos. DIP Jumper
P204 CA-6 26 Conductor Ribbon Assembly
R101 R-1-68K 68KΩ, 1/4w carbon
R102 RN-4-4.7K 4.7KΩ x 7 SIP
R104 RN-2-470 470Ω x 5 SIP
R201-R203 RN-1-10K 10KΩ x 9 SIP
R205 R-2-39 39Ω, 1w carbon
R206 R-1-100 100Ω, 1/4w carbon
R207 R-1-1K 1KΩ, 1/4w carbon
S201-S203 SW-6-8 8 Pole DIP
S205 SW-11 8 Pole DT Push Push
U101 IC-1 MC68B09P Microprocessor
U102 Serial488A-600 Programmed EPROM
U103 IC-78 84256-15 32K x 8 CMOS SRAM
U104 IC-23 65B22 Versitile Interface Adapter
U105 IC-16 R6551AP UART
U106 IC-3 TMS9914ANL IEEE Controller
U107 IC-4 SN75160BN IEEE Driver
U108 IC-5 SN75162BN IEEE Driver
U110 Macro488-601 Programming Equation - 16L8 PAL
U113 IC-33 74LS04 Hex Inverter
U201-U203 IC-39 74HCT244 Octal Buffer
U205 IC-21 SN74LS139 Dual Decoder
U206 IC-30 LM7805CT Regulator - +5v
U207 IC-38 26LS30 RS-423 Driver
U208 IC-36 26LS33 RS-422 Receiver
U209 IC-82 LT1081 RS-232 Transceiver
Y101 CR-4 7.3728 MHz Crystal

6.5

6.7 Serial488A/OEM Mechanical Dimensions

2.975

1.125

2 3 2

R

S

0.050

Mounting

C

Holes

7.80

7.60

0.156 Dia [4 Places]

0.050
I

E E E

Holes

Mounting

4 8 8

4.10

4.30

2.97

6.7

1.13

0.20

DATUM 'B'

0.20

DATUM 'A'

IEEE Connector Mounting & Hole Punch Out

G

dia. 2
places

0.320

PCB

ABCDEFG

1.842 0.921 1.578

C

D

C

L

C

L

B

A

0.789 0.640 0.320 0.194

Note: Does not imply orientation

0.200 Radius typ

F

E

10° typ

6.8

6.8 Replaceable Parts List - Serial488A/OEM
Schematic Part Number Description

C101-C114 C-5-.1 Ceramic, 25v
C116-C118 C-5-.1 Ceramic, 25v
C119,C120 C-5-15p Ceramic, 25v
C121-C125 C-2-10 Electrolytic - 25v
C126 C-5-1 Ceramic, 25v
D101 RF-1 Small Signal Diode
D102-D106 DD-2 Red PC Mount
J101 CN-2 IEEE 488 Connector
J102 CN-5-12 12 x 2 0.1" Header
J103 CN-32-2 2 Position power connector
J104 CN-8-25 PC Mount Female DB-25
J105 CA-19-8 8 Pos. DIP Jumper
R101 RN-4-4.7K 4.7KΩx 7 SIP
R102 R-1-68K 68KΩ, 1/4w carbon
R103 R-1-1K 1KΩ, 1/4w carbon
R104 RN-2-470 470Ω x 5 SIP
R105 R-1-100 100Ω, 1/4w carbon
R106-R108 RN-1-10K 10KΩ x 9 SIP
S101-S103 SW-6-8 8 Pole DIP
U101 IC-1 MC68B09P Microprocessor
U102 Serial488A-600 Programmed EPROM
U103 IC-78 84256-15 32K x 8 CMOS SRAM
U104 IC-23 65B22 Versitile Interface Adapter
U105 IC-16 R6551AP UART
U106 IC-3 TMS9914ANL IEEE Controller
U107 IC-4 SN75160BN IEEE Driver
U108 IC-5 SN75162BN IEEE Driver
U109 Macro488-601 Programming Equation - 16L8 PAL
U110 IC-33 74LS04 Hex Inverter
U111 IC-21 SN74LS139 Dual Decoder
U112-U114 IC-39 74HCT244 Octal Buffer
U116 IC-38 26LS30 RS-423 Driver
U117 IC-36 26LS33 RS-422 Receiver
U118 IC-82 LT1081 RS-232 Transceiver
Y101 CR-4 7.3728 MHz Crystal

6.9

6.9 Serial488/512K Motherboard Component Layout

DD-2

D102

DD-2

D106

DD-2

D105

C-5-.1

DD-2

D104

D103

DD-2

SW-6-8

C-5-15p

C118

Y101

C-5-.1

C101

C106

C-5-.1

C104

C-5-.1

D101

RF-1

C-5-.1

CR-4

U104

U105

R101

C103

C-5-.1

C102

C117

SO-1-40

R-1-68K

U103

U102

U101

RN-4-4.7K

SO-1-28

SO-1-28

SO-1-28

SO-1-40

6522

IC-23

6551

IC-16

84256
IC-78

R102

C-2-10

C124

C-5-.1

C105

C-5-.1

C110

+

+

J104

U110

C114

C-5-.1

C119 C121

U113

C113

CN-5-13

SO-1-20

16L8 PAL

Macro488-601

LT1081

IC-82

++

++

C-2-10 (4)

74LS04

IC-33

C120C122

R104

R103 RN-1-10K

RN-2-470

OPEN

S102

C-5-1

Jumper

12

3

4

5

678

C123

SW3

R106

6.10

R-1-1K

6.10 Serial488/512K I/O Board Component Layout

.33

.33

.33

.33

.33

.33

.33

SW1

41256-15

SW-6-8

OPEN

SO-1-40

.33

C-2-100

+

+

U216

1

234

5

6

7

8

U207

41256-15

.33

U215

41256-15

RN-1-10K

C-5-.1

41256-15

.33

41256-15

SW-6-8

IC-39

74HCT244

68B09

IC-1

U206

U214

OPEN

SW2

U205

41256-15

.33

U213

41256-15

1
234

5
6
7
8

41256-15

.33

41256-15

RN-1-10K

74HCT244

C-5-.1

U204

U212

IC-39

U203

41256-15

.33

U211

41256-15

IC-32

74LS373

C-5-.1

IC-48

74HCT240

U202

41256-15

.33

U210

41256-15

74HCT240

IC-48

U201

41256-15

.33

U209

41256-15

RN-3-47

.33

41256-15

IC-48

74HCT240

U208

RN-3-47

IC-48

74HCT240

C-5-.1

C-5-.1

C-5-.1

75160

IC-4

C-5-.1

TMS9914ANL

IC-3

CN-2

75162

IC-5

J101

74LS138

74LS08

C-5-.1

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

IC-8

C-5-.1

IC-49

74LS139

74LS04

C-5-.1

C-5-.1

IC-21

IC-33

C-5-.1

C-5-.1

74HCT00

C-5-.1

IC-34

6.11

6.11 Replaceable Parts List - Serial488/512K

Schematic Part Number Description

C101-C105 C-5-.1 0.1µF, 25v ceramic
C110 C-5-.1 0.1µF, 25v ceramic
C113,C114 C-5-.1 0.1µF, 25v ceramic
C117,C118 C-5-15p 15pF, ceramic
C119-C122 C-2-10 10µF, 25v electrolytic
C123 C-5-1 1µF, 25v ceramic
C124 C-2-10 10µF, 25v electrolytic
C201-C216 C-5-.33 0.33µF, 25v ceramic
C217-C232 C-5-.1 0.1µF, 25v ceramic
C233 C-2-100 100µF, 25v electrolytic

D101 RF-1 1N914 diode
D102-D106 DD-1 LED, Dialight #550-2406

J101 CN-11 Power Connector SWCR #712A
J102 CN-19-25 25 Pin Sub-D Female
J103 CN-2 IEEE Connector

J202-J203 CA-20 20 Circuit Jumper Cable

R101 R-1-68K 68KΩ, 1/4w, 10% carbon
R102 RN-4-4.7K 4.7KΩ x 7 SIP Network
R103 RN-1-10K 10KΩ X 9 SIP Network
R104 RN-2-470 470Ω X 5 SIP Network
R106 R-1-1K 1KΩ, 1/4w, 10% carbon

R201-R202 RN-3-47 47Ω X 8 DIP Network
R204,R205 RN-1-10K 10KΩ x 9 SIP Network

S101 SW-8 Power Switch
S102 SW-6-8 8 pole DIP switch
S201,S202 SW-6-8 8 pole DIP switch

U102 IC-10 2764-35 EPROM
U103 IC-78 84256 CMOS RAM
U104 IC-23 6522 VIA
U105 IC-16 6551 UART

U110 Macro488-601 Programmed 16L8 PAL
U113 IC-33 74LS04
U114 IC-82 LT1081

6.12

Schematic Part Number Description

U201-U216 IC-46 256K DRAM 150NS
U217 IC-50 74LS373 Octal Tri-State D
U218 ,U219 IC-14 74HCT244 Octal Buffer
U220-U223 IC-48 74HCT240 Inverting Buffer
U224 IC-1 MC68B09 Microprocessor
U225 IC-34 74HCTOO Quad NAND
U226 IC-21 74LS139 Dual Decoder
U227 IC-8 74LS138 Decoder
U228 IC-3 TMS9914ANL
U229 IC-33 74LS04 Hex Inverter
U230 IC-49 74LS08 Quad AND Gate
U231 IC-5 75162 IEEE Driver
U232 IC-4 75160 IEEE Driver

Y101 CR-5 8.000 MHz Crystal

TR-4 Power Supply ; 115V AC
TR-4E Power Supply ; 220V AC

6.13

Sample Programs

10 REM *** DUMB TERMINAL PROGRAM FOR THE Serial488A
20 REM *** Running under IBM Basica
30 REM *** This Program allows direct interaction between the
40 REM *** IBM-PC and an IEEE bus device through the Serial488A.
50 REM *** The Serial488A must be configured as the IEEE bus
60 REM *** controller and have talk back on terminator enabled.
70 REM ***
80 REM ***
90 REM ***
100 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

A.1

Appendix B Character Codes and IEEE Multiline Messages

$00 $10 $20 $30 $40 $50 $60 $70

0

NUL

$01 $11 $21 $31 $41 $51 $61 $71

1

SOH

GTL LLO
$02 $12 $22 $32 $42 $52 $62 $72

2

STX

$03 $13 $23 $33 $43 $53 $63 $73

3

ETX

$04 $14 $24 $34 $44 $54 $64 $74

4

EOT

SDC DCL
$05 $15 $25 $35 $45 $55 $65 $75

5

ENQ

PPC PPU
$06 $16 $26 $36 $46 $56 $66 $76

6

ACK

$07 $17 $27 $37 $47 $57 $67 $77

7

BEL

$08 $18 $28 $38 $48 $58 $68 $78

8

BS

GET SPE
$09 $19 $29 $39 $49 $59 $69 $79

9

HT

TCT SPD
$0A $1A $2A $3A $4A $5A $6A $7A

10

LF

$0B $1B $2B $3B $4B $5B $6B $7B

11

VT

$0C $1C $2C $3C $4C $5C $6C $7C

12

FF

$0D $1D $2D $3D $4D $5D $6D $7D

13

CR

$0E $1E $2E $3E $4E $5E $6E $7E

14

SO

$0F $1F $2F $3F $4F $5F $6F $7F

15

SI

ACG UCG

DLE

DC1

DC2

DC3

DC4

NAK

SYN

ETB

CAN

EM

SUB

ESC

FS

GS

RS

US

16

00

17

01

18

02

19

03

20

04

21

05

22

06

23

07

24

08

25

09

26

10

27

11

28

12

29

13

30

14

31

15

SP

%

&

32

16

33

!

17

34

"

18

35

#

19

36

$

20

37

21

38

22

39

'

23

40

(

24

41

)

25

42

*

26

43

+

27

44

,

28

45

-

29

46

.

30

47

/

UNL

48 64 80 96 112

0

1

2

3

4

5

6

7

8

9

:

;

<

=

>

?

@

00

49

65

A

01

50

66

B

02

51

67

C

03

52

68

D

04

53

69

E

05

54

70

F

06

55

71

G

07

56

72

H

08

57

73

I

09

58

74

J

10

59

75

K

11

60

76

L

12

61

77

M

13

62

78

N

14

63

79

O

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

UNT

Q

R

U

V

W

X

Y

P

81

SCG

`

SCG

97

a

SCG

82

SCG

98

b

SCG

83

S

SCG

84

T

SCG

85

SCG

99

c

SCG

100

d

SCG

101

e

SCG

86

SCG

102

f

SCG

87

SCG

103

g

SCG

88

SCG

104

h

SCG

89

SCG

105

i

SCG

90

Z

SCG

91

[

SCG

92

\

SCG

93

]

SCG

94

^

SCG

95

_

SCG

SCG

106

j

SCG

107

k

SCG

108

l

SCG

109

m

SCG

110

n

SCG

111

o

SCG

p

113

q

114

r

115

s

116

t

117

u

118

v

119

w

120

x

121

y

122

z

123

{

124

|

125

}

126

~

127

DEL

LAG TAG SCG

ACG = Addressed Command Group
UCG = Universal Command Group
LAG = Listen Address Group

TAG = Talk Address Group
SCG = Secondary Command Group

B.1