Measurement PC-CARD-DAS16330 User Manual

Parallel488

Bus Converter

INSTRUCTION MANUAL

IOtech, Inc. • 25971 Cannon Road • Cleveland, Ohio 44146 • [phone]

Warranty Information

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], e-mail: [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 Notice

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, Cautions, Notes, and Tips

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 i n ways other than described in t his manual can present serious safety hazards or cause equipment
damage.

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. As applicable, IOtech calibrates its
hardware to published specifications. Periodic hardware calibration is not covered under the warranty and must be performed by qualified personnel as specified in this
manual. Improper calibration procedures may void the warranty.

Quality Notice

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

Parallel488

User's Manual

138-0920

Revision 3.1

January 1992

IOtech, Inc.

" 25971 Cannon Road " Cleveland, Ohio 44146 " [phone]

Table of Contents

Section 1 Introduction Page

1.1 Description 1.1

1.2 Specifications 1.2

1.3 Abbreviations 1.3

Section 2 Getting Started Page

2.1 Inspection 2.1

2.2 Configuration 2.1

2.2.1 IEEE Address Selection 2.2

2.2.2 Auto-Linefeed Selection 2.3

2.2.3 Mode Selection 2.4

2.3 Operation 2.4

Section 3 Parallel To IEEE Operation Page

3.1 Parallel To IEEE 488 Mode Operation 3.1

3.2 Parallel Data Tran sf er s 3.1

3.3 IEEE Address Selection 3.2

3.4 Plo tter Applications 3.2

3.5 Printer Applications 3.4

3.6 Parallel Interface Descriptions and Timing 3.4

Section 4 IEEE To Parallel Operation Page

4.1 IEEE To Parallel Mode Operation 4.1

4.2 IEEE Data Transfers 4.1

4.2.1 Blind Bus Data Transfers 4.1

4.2.2 Controlled Bus Data Transfers 4.2

4.3 Ser ial Poll Status Byte Register 4.3

4.4 IEEE 488 Bus Implementation 4.4

4.4.1 My Talk Address (MTA) 4.4

4.4.2 My Listen Address (MLA) 4.5

4.4.3 Device Clear (DCL and SDC) 4.5

4.4.4 Interface Clear (IFC) 4.5

4.4.5 Serial Poll Enable (SPE) 4.5

4.4.6 Serial Poll Disable (SPD) 4.5

4.4.7 Unlisten (UNL) 4.5

4.4.8 Untalk (UNT) 4.6

Table of Contents

Section 4 IEEE To Parallel Operation Page

4.5 IEEE Address Selection 4.6

4.5.1 Listen Only Mode 4.6

4.6 Parallel Interface Description and Timing 4.7

Section 5 IEEE 488 Primer Page

5.1 History 5.1

5.2 General Structure 5.1

5.3 Send It To My Address 5.4

5.4 Bus Management Lines 5.4

5.4.1 Attention (ATN) 5.4

5.4.2 Interface Clear (IFC) 5.5

5.4.3 Remote Enable (REN) 5.5

5.4.4 End Or Identify (EOI) 5.5

5.4.5 Service Request (SRQ) 5.5

5.5 Handshake Lines 5.6

5.5.1 Data Valid (DAV) 5.6

5.5.2 Not Ready For Data (NRFD) 5.6

5.5.3 Not Data Accepted (NDAC) 5.6

5.6 Data Lines 5.7

5.7 M ultiline Commands 5.7

5.7.1 Go To Local (GTL) 5.7

5.7.2 Listen Address Group (LAG) 5.8

5.7.3 Unlisten (UNL) 5.8

5.7.4 Talk Address Group (TAG) 5.8

5.7.5 Untalk (UNT) 5.8

5.7.6 Local Lockout (LLO) 5.8

5.7.7 Device Clear (DCL) 5.8

5.7.8 Selected Device Clear (SDC) 5.9

5.7.9 Serial Poll Disable (SPD) 5.9

5.7.10 Serial Poll Enable (SPE) 5.9

5.7.11Group Execute Trigger (GET) 5.9

5.7.12Take Control (TCT) 5.9

5.7.13Secondary Command Group (SCG) 5.9

5.7.14Parallel Poll Configure (PPC) 5.10

5.7.15Parallel Poll Unconfigure (PPU) 5.10

5.8 More On Service Requests 5.10

Table of Contents

5.8.1 Serial Poll 5.11

5.8.2 Parallel Poll 5.11

Section 6 Service Information Page

6.1 Factory Service 6.1

6.2 Theory of Operation 6.1

6.3 Component Layout (Mother Board) 6.2

6.4 Component Layout (I/O Board) 6.3

6.5 Replaceable Parts List 6.4

Appendix A ASCII Character Codes A.1

Section 1 Introduction

Introduction

1.1 Description

The Parallel488 is an intellegent Bus Converter that provides transparent
conversion from an IEEE 488 device to a parallel (Centronics) device, or from a
parallel device to an IEEE 488 device. Common applications include
interfacing an IBM PC's parallel port to the IEEE port on an HP plotter, or
interfacing an IEEE controller to a parallel printer.

A buffer capable of storing 24,000 characters is built-in to the
Parallel488, allowing the computer to unload an entire document, and proceed
to another task while the Parallel488 spools data to the receiving device. The
Parallel488 spools characters to the receiving device until the Parallel488's
buffer is empty. Also included in the Parallel488 is the capability to
automatically insert a line-feed character upon receipt of carriage-return
character. This is useful in assuring compatability with a wide variety of
computers, instruments, printers, and plotters.

1.1

Section 1 Introduction

1.2 Specifications

IEEE 488-1978
Implementation: C1, C2, C3, C4 and C28 controller
subsets.(Parallel to IEEE)

SH0, AH1, T0, TE0, L4, LE0, SR0, RL0, PP0,
DC1, DT0, E1.

Connector: Standard IEEE 488 connector with metric studs.

Parallel (Centronics)
Terminator: Selectable Auto-LF (IEEE to Parallel).
Connector: Standard 36-pin male Centronics style

General
Data Buffer: 24,000 characters
Indicators: LEDs for IEEE Talk and Listen, Parallel 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" x2.68").
Weight: 1.55 kg. (3.6 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 Switch (external), IEEE

parameter switches (internal).

and parallel

Specifications subject to change without notice.

1.2

Section 1 Introduction

1.3 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

1.3

Section 2 Getting Started

Getting Started

2.1 Inspection

The Parallel488 was carefully inspected, both mechanically and electrically, 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 damage found to the shipping agent.
Remember to retain all shipping m aterials in the ev ent that shipment back to the facto ry
becomes necessary.

Every Parallel488 is shipped with the following....



Parallel488 Bus Converter Interface



138-0920 Instruction Manual





TR-2 Power Supply [110v] or





TR-2E Power Supply [220/230v]



Note: Other accessories ordered may be packaged and shipped separately.

2.2 Configuration

The Parallel488 has two modes of operation; as a parallel to IEEE 488 converter,
or as an IEEE 488 to parallel converter. A DIP switch internal to the Parallel488
determines which one of these modes the product will assume. Also selectable is the
automatic insertion of a line feed character after receipt of a carriage return, and the IEEE
address (for the IEEE to parallel mode only). On the following page are the Parallel488
factory default settings.

2.1

Section 2 Getting Started

SW1 Factory Default Settings

Switch

Side
View

DOT

IEEE Address
Auto Linefeed

Mode

12345678

OPEN

10

Disabled

Parallel to IEEE

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 parallel cables prior to dissassembly.

WARNING

Never open the Parallel488 case while it is conn ected
to the AC line. Failure to obser ve this warning may
result in equipment failure, personal injury or death.

Remove the four screws located in each corner of the rear panel. Hold the case
firmly and pull the rear panel outward, noting the slot location of the main circuit board.
Modify those parameters which are
unit. Slide the main

circuit board into the previously noted slot and finish reassembly by

appropriate for your installation and reassemble the

tightening the four screws into the rear panel.

2.2

Section 2 Getting Started

SW1 View for IEEE Bus Address Selection

12345678

0
1

OPEN

IEEE Address = 10

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

+

Switch

Side
View

= 0
= 8
= 0
= 2
= 0

DOT

When all switches are in the "open" position (addr ess 3 1) , the Para llel488 is

Listen Only

in the

mode. This mode enables a

TALK ONLY

device, such as an
digital voltmeter or data logger, to send data directly to the Parallel488 without
requiring a controller.

2.2.2 Auto-Linefeed Selection

Switch SW1-6 selects whether auto-linefeed is selected. When SW1-6 is in
the "closed" position, no extra characters are added to received data. When SW1-6
is in the "open" position, the Parallel488 automatically inserts a linefeed character

the data stream after receiving a carriage-return. This feature is necessary

into
when both the data source does not send line feeds with each carriage-return, and
the receiving device does not insert linefeeds upon receipt of a carriage-return.

This feature is functional in both operating modes of the Parallel488. The
factory default condition is auto-linefeed disabled. It will become immediately
evident

that this feature should be enabled if your printed material all appears on

one line.

2.3

Section 2 Getting Started

SW1 View for Auto-Linefeed Selection

12345678

OPEN

Auto-Linefeed Disabled Auto-Linefeed Enabled

12345678

OPEN

Switch

Side
View

DOT

2.2.3 Mode Selection

The Parallel488 mode is selected with SW1-7 in either the parallel to IEEE
mode (described in Section 3), or the IEEE to parallel mode (described in Section

4). The product operates in only one of two modes, and cannot communicate in
both modes simultaneously. The factory default is the parallel to IEEE mode.

SW1 View for Mode Selection

12345678

OPEN

IEEE to Parallel Mode Parallel to IEEE Mode

2.3 Operation

12345678

OPEN

Switch

Side
View

DOT

After setting the Parallel488 to the proper switch selections and reassembling the

unit, 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 th is caution

result in damage to the Parallel488.

may

2.4

Section 2 Getting Started

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 the AC line power. Place the rear panel power switch in the ON [1] position.
All front panel indicators should light for approximately one second while the Parallel488
performs an internal ROM and RAM self check. At the end of this self check all
indicators except POWER should turn off. If any of the following LED conditions exist
after power-on, a failure has occurred.

SYMPTOM FAILURE
All lights remain on ROM test has failed
All lights blink continually RAM test has failed
An LED does not blink LED has failed
No LEDs blink Power supply has failed

If any of the above symptons occur, cycle the power

be sure of the problem. If the problem is unresolved, refer to the Service Information
section of this manual.

If proper operation is obtained, turn-off the Parallel488 power switch, and connect

a parallel interface cable to the rear of the Parallel488. Connect the other end of the cable
to the device having the parallel interface. Now connect the IEEE cable to the rear of the
Parallel488, and the other end to the IEEE device.

Now apply power to both the IEEE device and the parallel device. The Parallel488

is now ready to perform the data transfer between both devices.

WARNING

connection through the
should only be connected to an IEEE bus device after first
being connected to the parallel device. Failure to do so may
allow the Parallel488 to float to a voltage away from ground.
This could result in damage to the interface, personal injury or
death.

The Parallel488 makes its earth ground

parallel interface cable. The unit

switch on the Parallel488 to

2.5

Section 3 Parallel To IEEE Operation

Parallel To IEEE Operation

3.1 Parallel to IEEE 488 Mode Operation

The Parallel To IEEE mode allows a parallel (Centronics) host device to send
data to single or multiple IEEE bus peripherals. The Parallel488 accepts characters on
its parallel port and outputs them to the IEEE port. The interface can buffer
approximately 24,000 bytes of data from the parallel port. Applications include
interfacing a listen-only or addressable IEEE printer/plotter to a parallel printer port.

The Parallel488 will refuse to accept more data from the parallel port when its
buffer memory is full. It does this by preventing completion of the parallel bus
handshaking sequence.

The Parallel488 also has the capability to automatically insert a line feed
character after receiving a carriage return character. This is necessary if the sending
parallel device does not automatically send a line feed and the receiving IEEE device
does not automatically insert a line feed. It will becom e immediately evident that this
feature should be enabled if your printed material all appears on one line.

3.2 Parallel Data Transfers

At power on, the Parallel488 sends an Interface Clear command on the IEEE
bus for greater than 100 microseconds. It then sends the following IEEE command
sequence ofÉ

ATN  UNL,UNT,LAG,*ATN

ALWAYS

LAG

includes all listen addresses from 0 to 30. This guarantees that

LISTEN ONLY

mode will also be ready to accept characters. The power-on

INIT

line is detected by the Parallel488 on the

3.1

In this sequence,
any printer or plotter attached to the Parallel488's IEEE port will be in the listen mode,
ready to accept characters. A device on the IEEE port which is in the

LISTEN

or
sequence is also initiated when the
parallel bus.

After all devices have received their listen address, the Parallel488 will accept
characters on its parallel port and output them to the IEEE port. If characters are

Section 3 Parallel To IEEE Operation

received

stores the characters until the IEEE bus can accept them. In the event

the buffer fills up entirely, the Parallel488 will hold off from accepting
data on the parallel port until sufficient buffer space is available to
proceed.

at a rate faster than can be output, the built-in 32,000 data buffer

3.3 IEEE Address Selection

It is not necessary to match the IEEE address on your printer or plotter
to an address on the Parallel488. The interface addresses all IEEE 488 devices
to listen. The address of the Parallel488 is automatically adjusted so that
address conflicts will not occur.

3.4 Plotter Applications

Some applications programs, such as Lotus 1-2-3ª, allow a graphics
output to a plotter via the PC's parallel (LPT) port. The Parallel488 can be used
to interface an IEEE 488 (HP-IB) plotter to the PC.

An IBM PC based Graphics System

3.2

Section 3 Parallel To IEEE Operation

To configure the PC graphics system, connect the LPT output of the PC
to the parallel input connector on the Parallel488 using a standard printer
interface cable. Using a standard IEEE 488 cable, connect the Parallel488's
IEEE output to the plotter's IEEE input.

After configuration, turn on the plotter followed by the Parallel488. The
Parallel488's front panel LEDs should all light momentarily while it performs
an internal ROM and RAM test. All LEDs should go out except for the Power
and Talk LED. The Talk LED indicates that the Parallel488 has detected the
plotter on the IEEE bus and has addressed it to listen.

When the parallel host begins to send the Parallel488 data, the Receive
LED will flash. If it does not, this indicates that the interface is not receiving
data from the parallel host. Verify the cables are connected properly and the
parallel cable wiring.

The following is an example of how the Parallel488 can be used to
communicate with an IEEE plotter through the PC's LPT port. The program
example is written in Basic on an IBM PC or compatible. It turn s the PC into a
dumb parallel terminal. When a key is pressed on the keyboard, the character is
transmitted out of the parallel (LPT1) port.

10 ' Terminal Program for the Parallel488
20 ' This Program allows direct interaction between
30 ' the IBM-PC and an IEEE plotter through the
Parallel488.
40 '
50 'Open the parallel communications port
60 OPEN "LPT1:" AS 1
70 ' Transmit key presses to the LPT1 port and
screen
80 K$=INKEY$
90 PRINT #1,K$; : PRINT K$;
100 GOTO 90 ' Do it again

below shows how to test the Parallel488's operation with a Hewlett
Packard 7470A plotter. O ther IEEE plotters are sim ilar but you should
refer to the plotter's programming manual for the proper command
syntax. Notice the Par allel488's fro nt panel L EDs as you type the plotter
commands.

Enter the program into the computer and run it. The example

3.3

Section 3 Parallel To IEEE Operation

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;

3.5 Printer Applications

Most of the information given for plotter applications applies to
applications for interfacing IEEE 488 printers to a parallel host. Some high end
printers have a secondary command setting which must be disabled for the
Parallel488 to control them. The Parallel488 does not use secondary commands
to control IEEE peripherals, such as printers or plotters. Refer to the printer's
instruction manual if the is a question as to whether the printer requires
secondary commands.

3.6 Parallel Interface Description and Timing

As a parallel to IEEE converter, the Parallel488 controls the following
signals (designated as
(designated as in).

out

in the following table) and responds to the signals

Pin Signal

1 STROBE

2 DATA0
3 DATA1
4 DATA2
5 DATA3
6 DATA4
7 DATA5
8 DATA6
9 DATA7

Direction Description
in When a low pulse is sent by the parallel

device (>0.5 µs), the Parallel488 reads
the character on the data lines and places
it in the IEEE output buffer.

in Least significant data bit 0 (high=logic "1")
in Data bit 1
in Data bit 2
in Data bit 3
in Data bit 4
in Data bit 5
in Data bit 6
in Most significant data bit 7

3.4

Section 3 Parallel To IEEE Operation

10 ACKNLG

11 BUSY

12 PE

13 SLCT

14 /AUTO FEED

16 Logic GND

19-30 Logic GND

31 /INIT

out The Parallel488 pulses this line low for

>5 µs after it has accepted a character
from the parallel device.

out The Parallel488 sets this line low when

it can accept another parallel character. If the
buffer is full, this line is set high until
the buffer again has space.

out Out of Paper signal. Not used. Always low.

out Printer Select signal. Not used. Always high.

in When this line is low and the present

parallel character is a carriage-return,
the Parallel488 will add a linefeed
character to the IEEE data stream.

Signal return.

Signal return.

in When a low pulse is received (>50 µs),

the buffer is cleared, Interface Clear (
asserted for 100 µs, and the Listener
Address Group is sent on the IEEE bus.

IFC

) is

32 /ERROR

33 Logic GND

36 /SLCT IN

out Off-Line signal. Not used. Always high.

Signal return.

in Printer Select Input. Not used.

3.5

Section 3 Parallel To IEEE Operation

Parallel to IEEE Mode Timing

Signal Dir

ACKNLG

BUSY

DATA

STROBE

out

out

in

in

5 µs min

0.5 µs min

3.6

Section 4 IEEE to Parallel Operation

IEEE to Parallel Operation

4.1 IEEE to Parallel Mode Operation

This mode of operation is useful in interfacing a parallel device, such as a
Centronics printer, to an IEEE controller or Talk Only device. Data which is sent by the
IEEE controller to the Parallel488 is buffered and transmitted out its parallel port. The
Parallel488 can buffer approximately 24,000 bytes of data from the IEEE input.

The Parallel488 will refuse to accept more data from the IEEE controller when its
buffer memory is full. It does this by preventing completion of the bus handshaking
sequences.

The Parallel488 also has the capability to automatically insert a line feed character
after receiving a carriage return character. This is necessary if the sending IEEE device
does not automatically send a line feed and the receiving parallel device does not
automatically insert a line feed. It will become immediately evident that this feature
should be enabled if your printed material all appears on one line.

When power is applied to the Parallel488, it will pulse the
parallel interface for approximately 50 microseconds. This is used to reset the parallel
device.

INIT

line on the

4.2 IEEE Data Transfers

The following methods may be used by the IEEE controller when sending data to
the Parallel488:

4.2.1 Blind Bus Data Transfers

If the IEEE controller does not mind waiting an indef inite time for data
space in the buffer to become available, the data can
Parallel488. This is referred to as blind data transfers because the IEEE
controller is blind as to whether or not the Parallel4 88 is capable of
data. In this case, the bus controller's output data transfer will be held off by the
Parallel488 if it is unable to buffer the data. It will resume accepting IEEE input
data when memory becomes available. This

4.1

simply be sent to the

accepting

Section 4 IEEE to Parallel Operation

type of control might be appropriate in a single user environment.

To illustrate how this would appear, let's assume the Parallel488 is
connected to a parallel printer which will accept data at 120 characters per
second. The IEEE bus controller is capable of sending data to the Parallel488 at a
rate of 5000 bytes per second. The data would be transferred on the bus at 5000
characters per second for slightly over five seconds, filling over 24,000 locations.
At that time, the IEEE input would hold off additional data transfers until
memory becomes available to buffer more data. The parallel devices 120 cps
would then become the average IEEE bus data acceptance rate.

If the controller is set to detect a data time-out error, then it will do so if
the Parallel488 holds off IEEE input data transfers for too long. The error can be
used to alert the operator to the problem, such as a printer out of paper, so that it
can be corrected. If the controller then restarts transmission exactly where it left
off, no data will be lost.

4.2.2 Controlled Bus Data Transfers

If the controller must avoid waiting for the parallel device, it can 'serial
poll' the Parallel488. 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
serial polls.

to determine the method of performing

When serial polled, the Parallel488 provides eight bits of status
information to the controller. One of the bits [
poll byte is set to a logic

EMPTY

is used to signify that all of the previous data sent to the interface has

transmitted to the parallel device. If it is NOT

been

sending any more data to the Parallel488. If this bit is a logic "1", then the

avoid
parallel device has accepted all previous data and the IEEE controller may send
more.

Another bit [
information concerning the IEEE input buffer. This bit is set to

"1" when the IEEE input buffer is

DIO2

] of the Serial Poll byte is used to indicate additional

DIO1

] of the Parallel488's serial

EMPTY

EMPTY

4.2

, the controller may

. The term

Section 4 IEEE to Parallel Operation

a logic "1" when there is 1024 or less locations in the buffer for data. It is
cleared, set to a logic "0", when there is greater than 2048 locations available.
This bit is referred to as the IEEE input buffer

FULL

bit.

4.3 Serial Poll Status Byte Register

The following shows and describes the serial poll status information provided by

the Parallel488.

Serial Poll Status Byte

1428163264128

DIO8 DIO7 DIO6 DIO5 DIO4 DIO3 DIO2 DIO1

DIO8

DIO7

DIO6

Not Used - Al ways '0'

Not Used - Al ways '0'

Not Used - Al ways '0'

Not Used - Al ways '0'

Not Used - Al ways '0'

Not Used - Al ways '0'

IEEE Input Bu ffer Full

IEEE Input Bu ffer Empty

Not Defined - Always "0"

rsv - Always "0"
This bit is defined by the IEEE 488 Specification and is used to
indicate to the bus controller which device requires service. This bit
is not supported by the Parallel488.

Not Defined - Always "0"

4.3

Section 4 IEEE to Parallel Operation

DIO5

DIO4

DIO3

DIO2

DIO1

Not Defined - Always "0"

Not Defined - Always "0"

Not Defined - Always "0"

IEEE Input Buffer Full
When this bit is set, it indicates that the Parallel488 may hold off the
controller on subsequent data transfers. The interface may continue
to accept an additional 512 characters.

IEEE Input Buffer Empty
When this bit is set, it indicates that the parallel device has accepted
all previous data sent to the Parallel488.

4.4 IEEE 488 Bus Implementation

The Parallel488 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 Parallel488 does not support or respond to include:

Remote Enable (REN)
Go to Local (GTL)
Group Execute Trigger (GET)
Local Lockout (LLO)
Take Control (TCT)
Parallel Poll (PP)
Parallel Poll Configure (PPC)
Parallel Poll Unconfigure (PPU)
Parallel Poll Disable (PPD)

4.4.1 My Talk Address

The Parallel488 does not support the transfer of data from the parallel port
to the IEEE controller except as it pertains to serial polls. This is due to the
unidirectional data transfer of the parallel interface.

(MTA)

4.4

Section 4 IEEE to Parallel Operation

4.4.2 My Listen Address

When the Parallel488 is addressed to listen, it accepts data from the active
talker, buffers it and outputs this data through the parallel interface. It will issue
a line feed character upon detection of a carriage return if the Auto Linefeed
feature is enabled.

4.4.3 Device Clear

Device Clear resets the Parallel488's IEEE input buffer and pulses the
parallel interface

(DCL and SDC)

INIT

4.4.4 Interface Clear

IFC places the Parallel488 in the Talker/Listener Idle State.

4.4.5 Serial Poll Enable

When Serial Poll Enabled, the Parallel488 sets itself to respond to a serial
poll with its serial poll status byte if addressed to talk. The Parallel488 will
continue to try to output its serial poll response u ntil it is 'Serial Poll Disabled ' by
the controller.

(MLA)

line. Any pending data is lost.

(IFC)

(SPE)

4.4.6 Serial Poll Disable

Disables the Parallel488 from responding to serial polls by the controller.

4.4.7 Unlisten

UNL places the Parallel488 in the Listener Idle State.

(UNL)

(SPD)

4.5

Section 4 IEEE to Parallel Operation

4.4.8 Untalk

(UNT)

UNT places the Parallel488 in the Talker Idle State.

4.5 IEEE Address Selection

SW1-1 through SW1-5 select the IEEE bus address of the Parallel488 when in

the IEEE to Parallel mode. The address is selected by simple binary weighting with SW1­1 being the least significant bit and SW1-5 the most significant. The following figure
shows the IEEE address of the Parallel488 set to 10.

SW1 View for IEEE Address Selection

12345678

0
1

OPEN

IEEE Address = 10

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

+

Switch

Side
View

= 0
= 8
= 0
= 2
= 0

DOT

4.5.1 Listen Only Mode

Listen Only is a special type of IEEE to Parallel operation. In the Listen
Only mode the Parallel488 accepts all data transmitted on the bus and transfers it
out its parallel port. The Parallel488 is set to Listen Only mode by setting its
address to 31 (switches SW1-1 through SW1-5 all open).

4.6

Section 4 IEEE to Parallel Operation

4.6 Parallel Interface Description and Timing

As an IEEE to parallel converter, the Parallel488 controls the following signals

(designated as

out

in the following table) and responds to the signals (desig nated as in).

Pin Signal

1 STROBE

2 DATA0
3 DATA1
4 DATA2
5 DATA3
6 DATA4
7 DATA5
8 DATA6
9 DATA7

10 ACKNLG

11 BUSY

ready to accept a new character. The

12 PE

13 SLCT

Direction Description
out After presenting a new character on the

parallel data lines (>1µs), this line is pulsed
low for >0.5 µs.

out Least significant data bit 0 (high=logic "1")
out Data bit 1
out Data bit 2
out Data bit 3
out Data bit 4
out Data bit 5
out Data bit 6
out Most significant data bit 7

in Low input indicates the parallel device has

accepted the character.

in Low input indicates the parallel device is

Parallel488 will not output a character
until this line is low.

in Out of Paper signal. Not used.

in Printer Select signal. Not used.

14 /AUTO FEED

16 Logic GND

19-30 Logic GND

out Always high.

Signal return.

Signal return.

4.7

Section 4 IEEE to Parallel Operation

31 /INIT

32 /ERROR

33 Logic GND

36 /SLCT IN

IEEE to Parallel Mode Timing

Signal Dir

ACKNLG

BUSY

DATA

STROBE

in

in

out

out

1 µs min

out The Parallel488 pulses this line low for

approx. 50 µs upon receipt of an IEEE 488
Device Clear, Selected Device Clear, or at
power on.

in Off-Line signal. Not used.

Signal return.

out Always low. Selects the external parallel device.

5 µs min

0.5 µs min

4.8

Section 5 IEEE 488 Primer

IEEE 488 Primer

5.1 History

The IEEE 488 bus is an instrumentation communication bus adopted by the Institute of Electrical
and Electronic Engineers in 1975 and revised in 1978. The Parallel488 conforms to this most recent
revision designated IEEE 488-1978.

Prior to the adoption of this standard, most instrumentation manufacturers offered their own
versions of computer interfaces. This placed the burden of system hardware design on the end user. If his
application required the products of several different manufacturers, then he might need to design several
different hardware and software interfaces. The popularity of the IEEE 488 interface (sometimes called the
General Purpose Interface Bus or GPIB) is due to the total specification of the electrical and mechanical
interface as well as the data transfer and control protocols. The use of the IEEE 488 standard has moved the
responsibility of the user from design of the interface to design of the high level software that is specific to
the measurement application.

5.2 General Structure

The main purpose of the GPIB is to transfer information between two or more devices. A dev ice
can either be an instrument or a computer. Before any information transfer can take place, it is first
necessary to specify which will do the talking (send data) and which devices will be allowed to listen
(receive data). The decision of who will talk and who will listen usually falls on the System Controller
which is, at power on, the Active Controller.

The System Controller is similar to a committee chair man. On a well run committee, only one
person may speak at a time and the chairman is responsible for recognizing members and allowing them to
have their say. On the bus, the device which is recognized to speak is the Active Talker. There can only be
one Talker at a time if the information transferred is to b e clearly understood by all. The act of "giving the
floor" to that device is called Addressing to Talk. If the committee chairman can not attend the meeting, or
if other matters require his attention, he can appoint an acting chairman to take control of the proceedings.
For the GPIB, this device becomes the Active Con tr oller.

5.1

Section 5 IEEE 488 Primer

At a committee meet ing, everyone present usually listens . This is not the case with the
GPIB. The Active Contr oller selects whic h devices will l isten and commands all other devic es to
ignore what is being transmitted. A devic e is instructed to listen by bein g Addressed to Listen.
This device is then referred to as an Active Listener. Devices which are to ignore the data
message are instructed to Unlisten.

The reason some devices are instructed to Unlisten is quite simple. Suppose a college instructor is
presenting the day's lesson. Each studen t 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 transfers information in a similar way. This method of data transfer is called
handshaking. More on this later.

For data transfer on the IEEE 488, the Active Controller mustÉ

a) Unlisten all devices to protect against eavesdroppers.
b) Designate who will talk by addressing a device to talk.
c) Designate all the devices who are to listen by addressing those

devices to listen.

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

5.2

Section 5 IEEE 488 Primer

}

D

DAVN

N

I

ATNSRQR

E

D

D

D

D

P

D

D

D

T

C

G

I

M

To Other Devices

evice 1

System Controller

Able to Talk,

Listen, and Control

ata Bus

evice 2

MM

Able to Talk

and Listen

evice 3

rinter

Only Able to Listen

ata Byte

ransfer
ontrol

eneral

nterface

anagement

evice 4
Frequency Counter
Only Able to Talk

IEEE 488 Bus Structure

Figure 5.1

5.3

RFD
DAC

FC

EN
OI

IO1-8

Section 5 IEEE 488 Primer

5.3 Send It To My Address

In the previous discussion, the terms Addressed to Talk and Addressed to Listen were used. These

terms require some clarification.

The IEEE 488 standard permits up to 15 devices to be configured within one system. Each of these
devices must have a unique address to avoid confusion. In a similar fashion, every building in town has a
unique address to prevent one home from receiving another home's mail. Exactly how each device's
address is set is specific to the 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 universal (multiline) commands from the Active Controller. These
commands include My Listen Address (MLA), My Talk Address (MTA), Talk Address Group (TAG), and
Listen Address Group (LAG).

5.4 Bus Management Lines

Five hardware lines on the GPIB are used for bus management. Signals on these lines are often
referred to as uniline (single line) commands. The signals are active low, i.e. a low voltage represents a
logic "1" (asserted), and a high voltage represents a logic "0" (unasserted).

5.4.1 Attention (ATN)

ATN is one of the most important lines for bus management. If Attention is asserted, then the
information contained on the data lines is to be interpreted as a multiline command. If it is not, th en
that information is to be interpreted as data for the Active Listeners. The Active Controller is the only
bus device that has control of this line.

5.4

Section 5 IEEE 488 Primer

5.4.2 Interface Clear (IFC)

The IFC line is used only by the System Controller. It is used to place all bus devices in a
known state. Although device configurations vary, the IFC command usually places the devices in the
Talk and Listen Idle states (neither Active Talker nor Active Listener).

5.4.3 Remote Enable (REN)

When the System Controller sends the REN command, bus devices will respond to remote
operation. Generally, the REN command should be issued before any bus programming is attempted.
Only the System Controller has control of the Remote Enab le line.

5.4.4 End or Identify (EOI)

The EOI line is used to signal the last byte of a multibyte data transfer. The device that is
sending the data asserts EOI during the transfer of the last data byte. The EOI signal is not always
necessary as the end of the data may be indicated by some special character such as carriage return.

The Active Controller also uses EOI to perform a Parallel Po ll by simultaneously asserting EOI
and ATN.

5.4.5 Service Request (SRQ)

When a device desires the immediate attention o f the Active Controller it asserts SRQ. It is
then the Controller's responsibility to determine which device requested service. This is
accomplished with a Serial Poll or a Parallel Poll.

5.5

Section 5 IEEE 488 Primer

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 line is controlled by the Talker. The Talker verifies that NDAC is asserted (active
low) which indicates that all Listeners have accepted the previous data byte transferred. The Talker
then outputs data on the bus and waits until NRFD is unasserted (high) which indicates that all
Addressed Listeners are ready to accept the information. When NRFD and NDAC are in the proper
state, the Talker asserts DAV ( active low) to indicate that the data on the bus is valid.

5.5.2 Not Ready for Data (NRFD)

This line is used by the Listeners to inform the Talker when they are ready to accept new data.
The Talker must wait for each Listener 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 line is also controlled by the Listeners. This line indicates to the Talker that each
device addressed to listen has accepted the information. Each device releases NDAC (high) at its
own rate, but the NDAC will not go high until the slowest Listener has accepted th e data byte.

5.6

Section 5 IEEE 488 Primer

1st Data Byte 2nd Data Byte

DIO1-8

(composite)

DAV

Source

Valid Not

Valid

Valid

Not
Valid

NRFD

Acceptor

NDAC

Acceptor

All

Ready

None

Accept

None

Ready

All

Accept

All

Ready

None

Accept

None
Ready

All

Accept

IEEE Bus Handshaking

5.6 Data Lines

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

use the convention of

DIO1

through

DIO8

instead of the binary designation of D0 to D7. The data lines are

bidirectional and are active low.

5.7 Multiline Commands

Multiline (bus) commands are sent by the Active Controller over the data bus with ATN asserted.

These commands include addressing commands for talk, listen, Untalk and Unlisten.

5.7.1 Go To Local (GTL)

This command allows the selected devices to be manually controlled. ($01)

5.7

Section 5 IEEE 488 Primer

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 LLO command prevents manual control of the instrument's functions. ($11)

5.7.7 Device Clear (DCL)

This command causes all bus devices to be initialized to a pre-defined or power up state. ($14)

5.8

Section 5 IEEE 488 Primer

5.7.8 Selected Device Clear (SDC)

This causes a single device to be initialized to a pre-defined or power up state. ($04)

5.7.9 Serial Poll Disable (SPD)

The SPD command disables all devices from sending their Serial Poll 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 SPE is sent and
ATN is unasserted. ($18)

5.7.11 Group Execute Trigger (GET)

This command usually signals a group of devices to begin executing a triggered action. This
allows actions of different devices to begin simultaneously. ($08)

5.7.12 Take Control (TCT)

This command passes bus control respon sibilities fr om the curren t Controller to anothe r dev ice
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

Section 5 IEEE 488 Primer

5.7.14 Parallel Poll Configure (PPC)

This configures devices capable of performing a Parallel Poll as to which data bit th ey are to
assert in response to a Parallel Poll. ($05)

5.7.15 Parallel Poll Unconfigure (PPU)

This disables all devices from responding to a Parallel Poll. ($15)

5.8 More On Service Requests

Most of the commands covered, both uniline and multiline, are the responsibility of the Active
Controller to send and the bus devices to recognize. Most of these happen routinely by the interface and
are totally transparent to the system programmer. Other commands are used directly by the user to provide
optimum system control. Of the uniline commands, SRQ is very important to the test system and the
software designer has easy access to this line by most devices. Service Request is the method by which a
bus device can signal to the Controller that an event has occurred. It is similar to an interrupt in a
microprocessor based system.

Most intelligent bus peripherals have the ability to assert SRQ. A DMM might assert it when its
measurement is complete, if its input is overloaded or for any of an assortment of reasons. A power supply
might SRQ if its output has current limited. This is a powerful bus feature that removes the burden from
the System Controller to periodically inquire, "Are you done yet?". Instead, the Controller says, "Do what I
told you to do and let me know when you're done" or "Tell me when something is wrong."

Since SRQ is a single line command, there is no way for the Controller to determine which device
requested the service without additional information. This information is provided by the multiline
commands for Serial Poll and Parallel Poll.

5.10

Section 5 IEEE 488 Primer

5.8.1 Serial Poll

Suppose the Controller receives a service request. For this example, let's assume there are
several devices which could assert SRQ. The Controller issues an SPE (Serial Poll enable)
command to each device sequentially. If any device responds with DIO7 asserted it indicates to the
Controller that it was the device that asserted SRQ. Of ten times th e oth er bits will indicate why the
device wanted service. This Serial Polling sequence, and any resu lting 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 SRQ is asserted, the Controller (under user's software)
conducts a Parallel Poll. The Controller must then analyze the eight bits of data received to
determine the source of the request. Once the source is determined, a Serial Poll might be used to
determine the why.

Of the two polling types, the Serial Poll is the most popular due to its ability to determine the who

and why. In addition, most devices support Serial Poll only.

5.11

Section 6 Service Information

Service Information

6.1 Factory Service

IOtech maintains a factory service center in Cleveland, Ohio. If problems are
encountered in using the Parallel488, you should first telephone the factory. Many
problems can be resolved through discussions 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

At the heart of the Parallel488 is a 6809 microprocessor [U201] supported by 8K
bytes of firmware EPROM [U102 (2764)] and 32K bytes of Static RAM [U103 (84256)].
A Versatile Interface Adapter [U104 (R65C22)] 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)].

Handshake lines for the parallel port are controlled by a programmable interface
adapter ("PIA") [U202 (6821)]. In the IEEE to parallel mode, this same PIA is used to
output 8 bits of data to the parallel port. In the parallel to IEEE mode, an 8 bit latch
[U206 (74LS373)] reads data from the parallel port.

Decoding of the microprocessor address space is accomplished with a
Programmable Logic Array [U110 (16L8)]. Below is the memory space allocation.

Address Device
$2000-$7FFF U103 84256 Static RAM
$8000 U206 74LS373 Parallel data receiver
$9200 U202 6821 Parallel handshake/data out
$A000 U106 9914A IEEE Controller
$B000 U104 R65C22 LED Driver
$E000-$FFFF U102 2764 Programmed EPROM

6.1

Part Number Function

Section 6 Service Information

6.5 Parallel488 Replaceable Parts List

Schematic Part Number

C101 C-5-.1 0.1uF, 25v ceramic
C102 C-5-.1 0.1uF, 25v ceramic
C103 C-5-.1 0.1uF, 25v ceramic
C104 C-5-.1 0.1uF, 25v ceramic
C105 Not Used
C106 C-5-.1 0.1uF, 25 v cer amic
C107 C-5-.1 0.1uF, 25v ceramic
C108 C-5-.1 0.1uF, 25v ceramic
C109 C-5-.1 0.1uF, 25v ceramic
C110 C-5-.1 0.1uF, 25v ceramic
C111 Not Used
C112 Not Used
C113 C-5-.1 0.1uF, 25v ceramic
C114 Not Used
C115 Not Used
C116 Not Used
C117 C-4-150p 150pF,1kv ceramic
C118 C-4-150p 150pF,1kv ceramic
C119 Not Used
C120 Not Used
C121 Not Used
C122 Not Used
C123 C-5-1 1uF, 25v ceramic
C201 Not Used
C202 Not Used
C203 C-5-.1 0.1uF,25v ceramic
C204 C-5-.1 0.1uF,25v ceramic
C205 C-5-.1 0.1uF,25v ceramic

D101 RF-1 1N91 4 di od e
D102 DD-2 LED, Dialight #550-2406
D103 DD-2 LED, Dialight #550-2406
D104 DD-2 LED, Dialight #550-2406
D105 DD-2 LED, Dialight #550-2406
D106 DD-2 LED, Dialight #550-2406
J101 CN-11 Pwr Connector SWCR #712A
J102 Not Used
J103 CN-2 IEEE Connector
J104 Not Used
J105 Not Used
J202 CA-1 5- 1 Centron ics Ca b le As sembly
J203 CA-19-9 9 Position DIP Jumper
J204 CA-20 20 Conductor Ribbon Assembly
J205 CA-20 20 Conductor Ribbon Assembly

Description

6.4

Section 6 Service Information

Schematic Part Number Description

R101 R-1-68K 68K½, 1/4w , 1 0% carbon
R102 RN-4-4.7K 4.7K½ x 7 SIP Ne tw ork
R103 RN-1-10K 10K½ x 9 SIP Network
R104 RN-2-470 470½ X 5 SIP Network
R105 R-2-39 39½, 1 W, 10% carbon
R106 Not Used
R107 Not Used
R201 R-1-1K 1K½, 1/4w, 10% carbon
R202 R-1-1K 1K½, 1/4w, 10% carbon
R203 R-1-4.7K 4.7K½, 1/4w, 10% carbon
R204 Not Used
R205 Not Used
R206 R-1-1K 1K½, 1/4w, 10% carbon

S101 SW-8 Power Switch
S104 SW-6-8 8 Pole Dip
S201 Not Used
S202 Not Used

U101 Not Used
U102 IC-40 MBM2764-45 EPROM
U103 IC-78 84256-15 32K x 8 CMOS
SRAM
U104 IC-23 R65C22 Versatile Interface
Adapter
U105 Not Used
U106 IC-3 TMS9914ANL IEEE Controller
U107 IC-4 SN75160AN Driver
U108 IC-5 SN75162N Driver
U109 IC-30 LM7805CT +5v Regulator
U110 Parallel488-601 Programming Equation - 16L8
PAL
U111 Not Used
U112 Not Used
U113 IC-33 74LS04 Hex Inverter
U114 Not Used
U115 Not Used
U116 Not Used
U201 IC-1 MC6809B Microprocessor
U202 IC-2 6821 PIA
U203 Not Used
U204 Not Used
U205 IC-47 74LS05 Hex Inverter/OC
outputs
U206 IC-32 SN74LS373 Octal Latch

Y101 CR-6 8.0000 MHz Oscillator

TR-2 Power Supply ; 115 volts AC
TR-2E Power Sup pl y ; 2 20 v ol t s A C

6.5

Appendix A Character Codes And IEEE Multiline Messages

A.1