Rockwell Automation 1770, D17706.5.16 User Manual

AllenBradley

DF1 Protocol and
Command Set

Reference
Manual

Important User Information

Because of the variety of uses for the products described in this
publication, those responsible for the application and use of this
control equipment must satisfy themselves that all necessary steps
have been taken to assure that each application and use meets all
performance and safety requirements, including any applicable laws,
regulations, codes and standards.

The illustrations, charts, sample programs and layout examples
shown in this guide are intended solely for purposes of example.
Since there are many variables and requirements associated with any
particular installation, Allen-Bradley does not assume responsibility
or liability (to include intellectual property liability) for actual use
based upon the examples shown in this publication.

Allen-Bradley publication SGI-1.1, Safety Guidelines for the

Application, Installation, and Maintenance of Solid-State Control

(available from your local Allen-Bradley office), describes some
important differences between solid-state equipment and
electromechanical devices that should be taken into consideration
when applying products such as those described in this publication.

Reproduction of the contents of this copyrighted publication, in
whole or in part, without written permission of Allen-Bradley
Company, Inc., is prohibited.

Throughout this manual we use notes to make you aware of safety
considerations:

ATTENTION: Identifies information about practices
or circumstances that can lead to personal injury or

!

Attention statements help you to:

death, property damage or economic loss.

• identify a hazard

• avoid the hazard

• recognize the consequences

Important: Identifies information that is critical for successful

application and understanding of the product.

PLC-5, DH+, PLC-2, PLC-3, PLC, SLC 500, SLC, SLC 5/01, SLC 5/02, SLC 5/03, SLC 5/04, ControlNet, MicroLogix, and
PLC-2/15 are trademarks of Allen-Bradley Company, Inc.
All other trademarks are property of their respective companies.

Summary of Changes

What's Changed in This
Document

About This Document

Changes to This Document

Change Description Reference

organization

commands

This document contains important information concerning the DF1
Protocol and Command Set Reference Manual.

This information extends and explains information provided in the
Data Highway/Data Highway Plust/DH-485 Communication
Protocol and Command Set Reference Manual, publication
1770-6.5.16 — November 1991

Changes to this document are indicated by a revision bar in the
margin.

The “look and feel” of your Allen-Bradley documentation has
changed! We’re constantly trying to improve our documentation to
make it more usable for you. If you have questions or comments
about this document, complete the enclosed Publication Problem
Report. In addition, we’ve also made the following changes to
publication 1770-6.5.16:

We've reorganized the reference manual to make it easier to find
information. We include a map" of this new organization.

We've added and updated the communication commands. We've
also organized them alphabetically. Additional commands include:

•apply port configuration

•change mode

•close file

•disable forces

•get edit resources

•initialize memory

•open file

•protected typed logical read with three address fields

•protected typed logical write with three address fields

•read diagnostic counters

•read section size

•return edit resource

Preface, page P-2

Chapter 7, Communication Commands"

Publication

17706.5.16 - October 1996

Table of Contents

What's Changed in This Document soc-i. . . . . . . . . . . . . .

About This Document soc-i. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Changes to This Document soc-i

About This Manual P-1. . . . . . . . . . . . . . . . . . . . . . . . . . .

Purpose of This Manual P-1. . . . . . . . . . . . . . . . . . . . . . . . . . .

Who Should Use This Manual P-1
What This Manual Contains P-2
Terms and Abbreviations P-3
Related
Related Products P-4
Conventions Used in This Manual P-5

Publications

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Network Layers 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Physical Layer 1-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DF1 Link 1-2
Network Link 1-2

DH Link 1-3
DH+ Link 1-5
DH485 Link 1-6

Software Layers 1-7

Datalink Layer 1-7
Application Layer 1-8

Message Packet Structure 1-9

Command and Reply Message 1-9
Message Priority 1-10
Delivery Order of Commands 1-10
Types of Commands 1-11
Error Codes 1-11

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P-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Understanding DF1 Protocol 2-1. . . . . . . . . . . . . . . . . . .

DF1 Protocol 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Halfduplex Protocol 2-2

Fullduplex Protocol 2-4
Character Transmission 2-5
Transmission Symbols 2-6

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Table of Contentsii

Using Halfduplex Protocols to Send and

Receive Messages 3-1. . . . . . . . . . . . . . . . . . . . . . .

Halfduplex Protocol Message Transmission 3-2. . . . . . . . . . . .

Transmitter and Receiver Message Transfer 3-3
Halfduplex Protocol Environment 3-3
Message Characteristics 3-7
Master

Polling Responsibilities
Duplicate
Inactive
Full Sinks 3-8
Simplified Network Layer 3-8

Slave Transceiver Actions 3-9
HalfDuplex Protocol Diagrams 3-11

Normal Message Transfer 3-12
Message T
Message Transfer with ACK Destroyed 3-13
Poll with No Message Available 3-13
Poll with Message Returned 3-14
Duplicate Message Transmission 3-15
Message Sink Full, Case 1 3-16
Message Sink Full, Case 2 3-17

Detection

Slave Polling

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ransfer with Invalid BCC/CRC

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3-7. . . . . . . . . . . . . . . . . . . . . .

3-7. . . . . . . . . . . . . . . . . . . . . . . . . . . .

3-7. . . . . . . . . . . . . . . . . . . . . . . . . . .

3-12. . . . . . . . . . . . .

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Using Fullduplex Protocol to Send and

Receive Messages 4-1. . . . . . . . . . . . . . . . . . . . . . .

Fullduplex Protocol Message Transmission 4-2. . . . . . . . . . . . .

Fullduplex Protocol Environment 4-3
Message Characteristics 4-4
Transmitter and Receiver Message Transfer 4-4

How the Transmitter Operates 4-5
How the Receiver Operates 4-7

Fullduplex Protocol Diagrams 4-10

Normal Message Transfer 4-10
Message Transfer with NAK 4-11
Message Transfer with T
Message Transfer with ReTransmission 4-13
Message Transfer with Message Sink Full 4-14
Message Transfer with NAK on Reply 4-15
Message Transfer with Timeout and ENQ for the Reply 4-16
Message Transfer with Message Source Full on the Reply 4-17

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imeout and ENQ

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4-12. . . . . . . . . . . . .

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Table of Contents iii

Datalink Layer Message Frames 5-1. . . . . . . . . . . . . . . .

Halfduplex Protocol Message Frames 5-2. . . . . . . . . . . . . . . . .

Polling Frame 5-2
Master Message Frame 5-2
Slave Message Frame 5-2

Fullduplex Protocol Message Frames 5-3

From user application program 5-3
From common application routines 5-3
Datalink layer frame 5-3

BCC and CRC Fields 5-4

BCC

Field
Halfduplex protocol example 5-4
Fullduplex protocol example 5-5

CRC

Field
Fullduplex and halfduplex slave protocol 5-7
Halfduplex master protocol 5-7
Use

this frame to validate the CRC

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5-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5-7. . . . . . . . . . . . . . . .

Application Layer Message Packets 6-1. . . . . . . . . . . . .

How Your Application Program Sends and Receives Messages 6-2

Message Packet Format 6-3. . . . . . . . . . . . . . . . . . . . . . . . . . .

Command 6-3
Reply 6-3
DST and SRC 6-4
Command 6-4
Reply 6-4
CMD and FNC 6-5
STS and EXT STS 6-6
TNS 6-7
ADDR 6-8
SIZE 6-8

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Communication Commands 7-1. . . . . . . . . . . . . . . . . . . .

command name 7-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

apply port configuration 7-4
bit write (write bit) 7-4
change mode 7-5
close

file

diagnostic status 7-6
disable forces 7-6
disable outputs 7-6
download all request (download) 7-7
download completed 7-7
download request (download privilege) 7-8

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7-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Table of Contentsiv

echo 7-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

enable outputs 7-9
enable PLC scanning 7-9
enter download mode 7-9
enter upload mode 7-10
exit download/upload mode 7-10
file read (read file) 7-10
file

write (write file)
get edit resource 7-11
initialize memory 7-12
modify

PLC2 compatibility file

file

open
physical read 7-13
physical write 7-14
protected
protected typed file read 7-16
protected
protected typed logical read with three address fields 7-17
protected typed logical write with three address fields 7-18
protected write 7-19
read bytes physical (physical read) 7-19
read diagnostic counters 7-19
read link parameters 7-20
read modifywrite (write bit) 7-20
readmodifywrite N 7-21
read section size 7-22
reset diagnostic counters 7-22
restart request (restart) 7-23
return edit resource 7-24
set data table size 7-24
set ENQs 7-25
set link parameters 7-25
set NAKs 7-25
set CPU mode 7-26
set

timeout
set variables 7-27
shutdown 7-28
typed read (read block) 7-28
typed write (write block) 7-30
unprotected
unprotected read 7-31
unprotected write 7-32
upload all request (upload) 7-33
upload completed 7-34
upload 7-34

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bit write

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typed file write

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bit write

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7-11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-12. . . . . . . . . . . . . . . . . . . . . .

7-13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-16. . . . . . . . . . . . . . . . . . . . . . . . . . .

7-27. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7-30. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents v

word range read (read block) 7-34. . . . . . . . . . . . . . . . . . . . . .

word range write (write block) 7-35
write bytes physical (physical write) 7-35
PLC5 Type/Data Parameter Examples 7-36
SLC

500 Information
Reading and Writing SLC 500 Data 7-38
Reading and Writing SLC 500 Data (using PLC2 terminology) 7-38

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7-38. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Message Packet Status Codes (STS, EXT STS) 8-1. . . . .

STS Byte 8-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Local STS Error Codes 8-2
Remote STS Error Codes 8-3

EXT STS Byte 8-3

DH485 EXT STS Codes 8-5

Remote STS and EXT STS Codes 8-5

Remote STS Codes from a PLC2 or 1774PLC Processor 8-5
Remote STS and EXT STS Codes from a PLC3 Processor 8-6

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Diagnostic Counters 9-1. . . . . . . . . . . . . . . . . . . . . . . . .

1747

Cat. Nos.
1747KE DH485 Diagnostic Counters 9-3
1747L20, L30, L40, L511, L514, L524, (SLC 500, 5/01, and

5/02 processors), 1747PA2x (SLC APS COM1), 1770KF3,
and 1784KR DH485 Diagnostic Counters 9-3

1747L541, L542, and L543 (SLC 5/04 processors)

DH+ Diagnostic Counters 9-4. . . . . . . . . . . . . . . . . . . . .

1747L541, L542, and L543 (SLC 5/03 and 5/04 processors)

DH485 Diagnostic Counters 9-5

1747L541, L542, and L543 (SLC 5/03 and SLC 5/04 processors)

DF1 Diagnostic Counters 9-6. . . . . . . . . . . . . . . . . . . . . .

1761

Cat. Nos.
1761L16AWA, L16BBB, L16BWB, L32AWA, L32BWA, L32BWB

(MicroLogix 1000 processors, Series C or later) DH485 Diagnostic
Counters 9-7

1761L16AWA, L16BBB, L16BWB, L32AWA, L32BWA, L32BWB

(MicroLogix 1000 processors) DF1 Diagnostic Counters 9-7

1770 Cat. Nos.

1770KF2 and 1771KE/KF DH and Asynchronous Link Diagnostic

Counters 9-8

1770KF2 and 1785KE DH+ and Asynchronous Link Diagnostic

Counters 9-11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1770KFC DF1 Diagnostic Counters 9-13

1771

Cat. Nos.
1771KA, 1771KA2, and 1774KA DH Diagnostic Counters 9-14

1771KC DH Diagnostic Counters 9-16. . . . . . . . . . . . . . . . . .

1771KG,KGM Diagnostic Counters 9-19

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. . . . . . . . . . . . . . .

. . . . . . . . .

. . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

9-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9-8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9-14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contentsvi

1775

Cat. Nos.
1775KA,S5,SR5 DH Diagnostic Counters 9-21
1775S5,SR5 DH+ Diagnostic Counters 9-23

1779

Cat. Nos.
1779KP5 DH+ Diagnostic Counters 9-24

1784

Cat. Nos.
1784KT and 1784KT2 DH+ Diagnostic Counters 9-25

1785

Cat. Nos.
1785KA DH Diagnostic Counters 9-26
1785KA DH+ Diagnostic Counters 9-27

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

1785KA3 DH+ Diagnostic Counters 9-28
1785KA5 DH+ Diagnostic Counters 9-29
1785KA5 DH485 Diagnostic Counters 9-30

. . . . . . . . . . .

. . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

. . . . . .

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . .

9-21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9-24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9-25. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9-26. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1785L11B, L20B, L30B, L40B, L60B, and L80B DH+ Channel

Diagnostic Counters 9-30. . . . . . . . . . . . . . . . . . . . . . . . .

1785L20E, L40E, L40L, L60L, L80E DH+ Diagnostic

Counters 9-32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5250

Cat. Nos.

5250LP1, LP2, LP3, LP4 DH+ Diagnostic Counters 9-33

. . .

9-33. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diagnostic Status Information 10-1. . . . . . . . . . . . . . . . . .

1747

Cat. Nos.

1747KE Status Bytes 10-2

. . . . . . . . . . . . . . . . . . . . . . . . . .

1747L20, L30, L40, L511, L514, L524 (SLC 500, SLC 5/01

and SLC 5/02 processors) Status Bytes 10-3. . . . . . . . . .

1747L532, L541, L542, L543 (SLC 5/03 and SLC 5/04 processors)

Status Bytes 10-4

1761, 1770, and 1771 Cat. Nos. 10-5

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .

1761L16AWA, L16BBB, L16BWB, L32AWA, L32BWA, L32BWB

(MicroLogix 1000 processors) Status Bytes 10-6

1770KF3 Status Bytes 10-7

. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . .

1771KA2, KA, KC/KD, KE, KF, KG, KGM, 1770KF2

Status Bytes 10-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1773, 1775, and 1779 Cat. Nos. 10-11

1773KA Status Bytes 10-11
1775KA, S5 and SR5 Status Bytes 10-13
1779KP5 Status Bytes 10-14

1784

Cat. Nos.
1784KR Status Bytes 10-15
1784KT, KT2 Status Bytes 10-15

1785

Cat. Nos.
1785KA Status Bytes 10-16
1785KA5 Status Bytes 10-17
1785KA3 Status Bytes 10-17
1785KE Status Bytes 10-19

. . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . .

10-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10-15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10-16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents vii

1785LT (PLC5/15) and 6008LTV (PLC5 VME)

Status Bytes 10-20

1785LT3 (PLC5/12) and 1785LT2 (PLC5/25)

Status Bytes 10-21

1785L11B, L20B, L20E, L30B, L40B, L40E, L40L,

L60B, L60L Status Bytes 10-22. . . . . . . . . . . . . . . . . . . .

5130

Cat. Nos.

5130RM1,RM2 (PLC5/250) Status Bytes 10-23

Data

Encoding

Numbering Systems 11-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Decimal 11-2

Binary 11-3

Binary Coded Decimal 11-3

Hexadecimal 11-4

Octal

Binary

Order

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Decimal Representation, Number 239 11-2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Binary Representation, Number 239 11-3

BCD Representation of Decimal 239 11-3

Hexadecimal Representation of Decimal 423 11-4

Octal Representation of Decimal 239 11-5

Floatingpoint

of T

ransmission 11-6. . . . . . . . . . . . . . . . . . . . . . . . . . . .

A 16Bit Word in PLC Memory 11-7
A 16Bit Computer Word with LefttoRight Byte and

Bit Order 11-7

A 16Bit Computer Word with RighttoLeft Byte and

Bit Order 11-7

A 16Bit Computer Word with LefttoRight Byte Order and

RighttoLeft Bit Order 11-7

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . .

. . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

10-23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11-5. . . . . . . . . . . . . . . . . . . . . . . . . . .

Uploading and Downloading with AB Processors 12-1. . .

Uploading from the Processor 12-2. . . . . . . . . . . . . . . . . . . . . . .

Uploading from a PLC2 Processor 12-2
Uploading from a PLC3 Processor 12-2
Uploading from a PLC5 Processor 12-3

Procedure 1  PLC5/15/B processors, revision E

and earlier 12-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Procedure 2 12-5

Uploading from an SLC 500 Processor 12-6

Downloading to the Processor 12-6

Downloading to a PLC2 Processor 12-7
Downloading to a PLC3 Processor 12-8
Downloading to a PLC5 Processor 12-8

Procedure 1 (PLC5/15/B rev E and earlier) 12-9
Procedure 2 12-10

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . .

Table of Contentsviii

Downloading to an SLC 500 Processor 12-10. . . . . . . . . . . . . .

Procedure 1  SLC 500, SLC 5/01 and SLC 5/02

Processors 12-11

Procedure 2  SLC 5/03 and SLC 5/04 Processors 12-12

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . .

PLC Addressing 13-1. . . . . . . . . . . . . . . . . . . . . . . . . . . .

PLC2/1774PLC Addressing 13-2. . . . . . . . . . . . . . . . . . . . . . .

PLC2/1774PLC Logical Addressing 13-2
PLC2 Physical Addressing 13-3
1774PLC Physical Addressing 13-3

PLC3 Addressing 13-4

PLC3 Logical Addressing 13-5
PLC3 Physical Addressing 13-7
PLC3 Symbolic Addressing 13-8

PLC5 Addressing 13-9

PLC5 Logical Addressing 13-10

PLC5 Logical Binary Addressing 13-11
PLC5/250 Logical Binary Addressing 13-13

Logical ASCII Addressing 13-15
PLC5 Physical Addressing 13-16
PLC5

Floating Point

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . .

. . . . . . . . . . . . .

13-17. . . . . . . . . . . . . . . . . . . . . . . . . . .

Line Monitor Examples 14-1. . . . . . . . . . . . . . . . . . . . . . .

Halfduplex Line Monitor Example 14-2. . . . . . . . . . . . . . . . . . . .

Message from master to slave and slave acknowledgement: 14-2
Message sent from slave to master in response to poll and

slave acknowledgement: 14-2

Poll with a DLE EOT in response: 14-2

Fullduplex PLC2 Line Monitor Example 14-3
Fullduplex PLC3 Line Monitor Example 14-6

. . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

. . . . . . . . . . . . . . .

ASCII Codes 151. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Preface

About This Manual

Read this preface to familiarize yourself with this manual.
This preface includes information on:

• the purpose of this manual

• who should use this manual

• what this manual contains

• terms and abbreviations used in this manual

• related publications

• related products

• conventions used in this manual

Purpose of This Manual

Who Should Use This Manual

Use this manual to:

• program a DF1 driver for a computer to interface to

Allen-Bradley DF1 products and to proprietary networks via
protocol bridges

• write applications for 1784-KT, -KT2, -KTX, -KTXD, -PCMK

communication interfaces using standard
Rockwell Software Inc. (RSI) driver products

• troubleshoot your network

Read this manual before you attempt to write a DF1 driver, or before
attempting to troubleshoot your network. We assume that you are
already familiar with:

• your serial device

• Allen-Bradley PLC processors

Before you begin writing your driver, make sure you have:

• a pocket calculator that adds, subtracts, multiplies, and divides in

decimal, hexidecimal, octal, and binary

• a serial protocol analyzer for displaying actual hex bytes sent to

and from a DH, DH+, or DH485 module

"

Writing drivers

As an alternative to writing your own driver, RSI provides RSLINX
C SDK (cat. no. 9355-WABC) and INTERCHANGE (cat. nos.
9351-AIX, -DKTS, -HPUS, -OSF, -VS, -WES, -WKTS) software.
These products provide an application programmer’s interface (API)
and a complete set of drivers to communicate with Allen-Bradley
processors via Ethernet, DH, DH+, DH485, and DF1 serial links on
various hardware and operating system platforms.

17706.5.16  October

, 1996

About This ManualP–2

What This Manual Contains

➊Network

Basics

Chapter 1,

Network Layers

➋Protocol

Chapter 2,

Understanding DF1
Protocol

Chapter

3,

Using Halfduplex
Protocol to Send and
Receive Messages

Chapter 4,

Using Fullduplex
Protocol to Send and
Receive Messages

This manual is divided into five units:

➌Message

Packets

Chapter 5,

Datalink Layer
Message Frames

Chapter 6,

Application Layer
Message Packets

Chapter 7,

Communication
Commands

Chapter 8,

Message Packet
Status Codes (STS,
EXT STS)

➍Module

Diagnostics

Chapter 9,

Diagnostic Counters

Chapter 10,

Diagnostic Status
Information

➎Reference

Chapter 1

1,

Data Encoding

Chapter 12,

Uploading and
Downloading

Chapter 13,

PLC Addressing

Chapter 14,

Line Monitor
Examples

➊ ➋ ➌ ➍ ➎

gain an understanding of
the network

•

understand what DF1
protocol is
understand the dif

•

between halfduplex and
fullduplex protocols

ference

•properly configure the

datalink layer of your
software driver
understand each part of a

•

message packet

•

learn message packet
formats for all commands

•asynchronous link status

codes that may be sent in
the STS fields of your
message packet

•diagnostic counters

contained in each interface
module
information returned from

•

each interface when your
computer sends a
diagnostic status command

Chapter 15,

ASCII Codes

•

data encoding and
conversion information
upload and download

•

procedures for the PLC2,
PLC3 and PLC5
processors
information on addressing

•

PLC2, PLC3, PLC5, and
PLC5/250 processors
line monitor examples that

•

show actual commands
being sent and provide an
explanation of each
example

•hex and binary values for

ASCII characters

17706.5.16  October

, 1996

About This Manual P–3

Terms and Abbreviations

Term Definition

local node The node sending the command

node The point at which devices, such as programmable controllers,

interface to the network. Each device on a network must have a
unique node address.

In some AllenBradley documentation, you may find the term station
used in place of the term node.

physical link Cable and associated hardware, such as transmitter and receiver

circuits.

PLC controller An AllenBradley programmable controller. See programmable

controller.

protocol Set of programming rules for interpreting the signals transmitted over

the physical link by nodes.

programmable

controller

remote node The node sending the reply to the local node

Abbreviation Definition

ACK acknowledgement. In communication, ACK is a control code sent by

DH+ Data Highway Plus. AllenBradley proprietary network protocol.

NAK negative acknowledgement.

a solidstate control system that has a userprogrammable memory
for storage of instructions to implement specific functions such as I/O
control, logic, timing, counting, report generation, communication,
arithmetic, and data file manipulation. A controller consists of central
processor, input/output interface, and memory. A controller is
designed as an industrial control system.

the receiving node to indicate that the data has been received
without error and the next part of the transmission may be sent.

Related Publications

Publication Name Publication Number

DH/DH+/DH II/DH485 Cable Installation Manual 17706.2.2

DH Overview Product Data 17702.39

DH+ Overview Product Data 17852.6

SCADA System Selection Guide AG2.1

SCADA System Application Guide AG6.5.8

17706.5.16  October

, 1996

About This ManualP–4

Related Products

Catalog Number Product Related Documentation

1747KE DH485/RS232 Interface Module 17472.3.7, product data

1770KF2 DH or DH+ Asynchronous (RS232 or RS422A) Interface

1770KF3 DH485 Asynchronous (RS232) Interface Module 17706.5.18, user manual

1771KA2 DH PLC2 Family Communication Adapter Module 17715.2, switch settings

1771KG PLC2 Family RS232 Interface Module 17712.32, product data

1771KGM SCADA Communication Master Module for PLC2 Family 17712.85, product data

1771KE,KF DH RS232 Interface Module 17716.5.16, user manual

1775KA DH PLC3 Communication Adapter Module 17756.5.1, user manual

1775S5,SR5 PLC3 I/O Scanner Module 17756.5.5, user manual

1784KR DH485 Personal Computer Interface Module 17842.23, installation data

1784KT DH+ PC Interface Module 17842.31, installation data

1784KT2/B DH+ PS/2 Interface Module 17842.21, installation data

1784KT2/C 17846.5.16, user manual

1784KTX DH+ PC Interface Module 17846.5.22, user manual

1784KTXD DH+ PC Interface Module

1784PCMK DH+/DH485 PCMCIA communication interface 17846.5.19, user manual

1785KA DH/DH+ Communication Interface Module 17852.6, product data

1785KA3 DH+ PLC2 Family Communication Adapter Module 17852.6, product data

1785KA5 DH+/DH485 Communication Interface Module 17856.5.5, user manual

1785KE DH+ RS232 Interface Module 17856.5.2, user manual

5130RM1,RM2 PLC5/250 Resource Manager Module 50006.2.1, design manual

9351AIX,
DKTS, HPUS,
OSF, VS,
WES, WKTS

9355WABC

Allen-Bradley offers a wide range of interfaces for the DH, DH+,
and DH485 networks, including:

Module

INTERCHANGEt Software

RSLINXt C SDK Software

17476.12, user manual

17706.5.13, user manual
17706.5.13RN1 release notes

17706.5.18RN1, release notes
17706.5.18RN2, release notes

17716.5.1, user manual

17716.5.8, user manual
17716.5.8DU1, document update

17716.5.39, user manual

17716.5.16DU1, document update

17842.23RN1, release notes

17856.5.1, user manual

17856.5.3, user manual
17856.5.3DU1, document update

50006.2.10, installation manual

50006.4.21, reference manual

9398WABCTD11.21.95, data sheet

17706.5.16  October

, 1996

About This Manual P–5

Conventions Used in This Manual

"

Communication, diagnostic, and driver software

DH 6001-NET Network Communications Software (Series 6001)
provides a DH driver for many DEC
information, refer to the DH/DH+/DH II

 computers. For more

 Network Communication

Software Overview (publication 6006-2.3).

We use these conventions in this manual:

This convention: Is used to:

"

call attention to helpful information

refer you to other AllenBradley documents that
might be useful

17706.5.16  October

, 1996

Network Basics

Network Layers  Chapter 1

Chapter 1

Network Layers

Your network is made up of several layers, including:

Nodes send data through the layers.

Application layer serves as the window through which applications access
communication services, including file transfers, virtual terminal functions, and email.

Presentation

Session

applications.

Transport layer performs segmentation and reassembly of messages.
Provides recovery from transmission errors.

Network

Datalink layer runs protocol to guard against errors, detects errors, and corrects

errors. Packages data and puts it onto the physical cable. Manages the flow of the
data bit stream into and out of each network node.

layer manages data formats for the applications.

layer establishes and terminates network communications between

layer establishes connections for communication between network nodes.

Physical layer transmits bits between communication devices.

In this chapter, we discuss the physical, data-link, and application
layers. (We refer to the data-link and application layers as the
software layers.) This chapter contains these sections:

Section Page

Physical Layer 1-2

Software Layers 1-7

Message Packet Structure

1-9

Publication

17706.5.16 - October 1996

1–2 Network Layers

Physical Layer

DF1 link

RS232 Network Interface

network link

DH/DH+/DH485 link

nodes

IBMPC XT, AT or
compatible computer

ControlNet
link

The physical layer is a set of cables and interface modules that
provides a channel for communication between the nodes. A node is
a connection point onto a network, typically containing a unique
address.

When you connect a computer serially to your DH, DH+, DH-485,
or ControlNet link, the interface module acts as an interface between
the:

• DF1 link (RS-232 or RS-422-A)

• network link (DH, DH+, DH485, ControlNet link)

DF1 Link

A DF1 link provides:

• master-slave communication through a half-duplex protocol

• peer-to-peer communication through a full-duplex protocol

This manual provides information necessary to write your own
driver for an intelligent device on a DF1 link. See “Software
Layers,” on page 1–7, for the layers your software driver must
implement so that your intelligent device can talk to other DH,
DH+, DH485, or ControlNet nodes.

Network Link

These network links are available for peer-to-peer communication:

This link Connects And allows See page

•PLC2, PLC3

processors

•color graphic systems

DH

DH+

DH485

ControlNet

➀

Using
up to 255 nodes.

•personal computers

•host computers

•programmable

RS232/RS422 devices

•same devices as DH

•PLC5 processors

•SLC 5/04 processor

•SLC 500 processors

•color graphic systems

•personal computers

•PLC5 processors

•I/O devices

•personal computers

•operator interface devices

bridges (e.g., 1785KA modules), you can extend the length of your DH network to contain

up to 64 nodes

up to 64 nodes 1-5

up to 32 nodes 1-6

up to 99 nodes --------

➀

1-3

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1–3Network Layers

DH Link

A DH link is a local area network (LAN) designed for factory-floor
applications. This link accepts 64 devices and can transmit 57.6 K
bits of data per second.

A DH link consists of a trunk cable up to 10,000 feet (3,048 meters)
long and drop cables as long as 100 feet (30.48 meters) each.
Each node is at the end of a drop cable and connects to the DH link
through a station connector (cat. no. 1770-SC). This is the only
configuration tested and supported by Allen-Bradley.

This processor Connects to a DH link through the

PLC2 family

PLC3

PLC5/250

PLC5, SLC 5/04

➀

Although a PLC5 processor does not directly connect to a DH link, it can communicate with
devices on a DH link via the 1785KA module.

DH PLC2 family communication adapter module
(cat. nos. 1771KA2, KG)

DH PLC3 family communication adapter module
(cat. nos. 1775KA,S5, SR5)

Resource manager module
(cat. nos. 5130KA, RM1,RM2)

DH+/DH communication module

➀

(cat. no. 1785KA)

A DH link implements peer-to-peer communication through a
scheme called the floating master. With this arrangement, each
node has equal access to become the master. The nodes bid for
temporary mastership based on their need to send information.

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1–4 Network Layers

Unlike a master/slave relationship, a floating master relationship
does not require the current master to poll each node to grant
permission to transmit. Therefore, it provides a more efficient
network because there is less overhead—i.e., time—per transaction.

SC

= station connector; 1770SC

PLC3 processor
cat. nos. 1775KA or S5

DH+ link

1785KA

personal computer

modem

modem

DH interface module
cat. nos. 1771KE, KF

SC SC SC SC SC SCSC

PLC2 family processor
cat. no. 1771KA2

RS232C link
(50 cableft. max.)

DH link

PLC2/30 processor

1771KG

PLC5/250 processor
5130RM1

modem

modem

1770KF2

1770KF2

RS232C link
(50 cableft. max.)

T60 industrial workstation running

iew software

ControlV

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1–5Network Layers

DH+ Link

A DH+ link is similar to a DH link, but is optimally used for smaller
networks consisting of limited nodes (about 15 maximum). A DH+
link accepts 64 devices and can transmit data at 57.6, 115.2, or

230.4K bits. (PLC-5/250, SLC, and PLC processors support 57.6
and 115.2K bits; SLC 5/04 processors support 230.4K bits; PLC-5
processors are expected to support 230.4K bits early in 1997.)

This processor Connects to a DH+ link

PLC2

PLC3

through the PLC2 Family Interface module
(cat. no. 1785KA3)

through the I/O Scanner Communication Adapter module
(cat. nos. 1775S5,SR5)

PLC5 directly

PLC5/250

SLC 5/04

➀

➀

You

can configure the data rate for SLC 5/04 processors.

through the Resource Manager module
(cat. nos. 5130KA, RM1, RM2)

directly

A DH+ link implements peer-to-peer communication with a
token-passing scheme to rotate link mastership among the nodes
connected to that link.

SC

= station connector; 1770SC

T71 with 1784KTx

SLC 5/04 processor

PLC3 processor
cat. no. 1775S5

DH link

1785KA

SC

PLC5 processor

T53 programming
terminal with 1784KT
installed

notebook computer
with 1784PCMK

PLC2 processor
cat. no. 1785KA3
(or any other PLC2
processor)

DH+ link

personal computer

1785KE

SCSC

RS232C link
(50 cableft. max.)

PLC5/250 processor
cat. no. 5130RM1

1770KF2

T60 industrial
workstation with
ControlV

iew software

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1–6 Network Layers

DH485 Link

A DH485 link is a low cost, peer-to-peer programming and
data-acquisition link for a variety of Allen-Bradley products.
DH485 topology is similar to DH and DH+ topology. You can
connect as many as 32 nodes to a DH485 link.

The DH485 link is based on the Electrical Industries Association
(EIA) Standard RS-485 Electrical Signalling Specification.
A variety of Allen-Bradley products (including SLC 500 controllers,
1784-KTX, 1747-KE, 1770-KF3, and operator interface devices) act
as token-passing masters on the DH485 link. This link also supports
a respond-only mode for low-level devices on the link, such as
Allen-Bradley bar code decoders.

A DH485 link implements peer-to-peer communication with a
token-passing scheme to rotate link mastership among the nodes
connected to that link.

T53 programming terminal with a
1784KTX card installed and running
6200 series software

1747AIC

RS232/RS485
converter

DTAM Plus
operator
interface

1747AIC

1747AIC

SLC 5/01 processor
in 17slot modular system

1747PIC

channel 1

À

PLC5 processor

DH+ link

SLC 5/04
processor

channel 0

DH485 link

1770KF3

1747AIC

PanelV

iew 550

operator terminal

SLC 500
fixed 30I/O
controller with
expansion chassis

1747AIC

remote I/O link

notebook compute
with 1784PCMK

1747SN

SLC 5/03
processor

to remote
I/O chassis

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À

T

o connect an SLC 5/04 to a 1747PIC,

use a 9pin (male) to 25pin (female) adapter.

1–7Network Layers

Software Layers

Your DF1 links and network links (DH, DH+, and DH485) each use
two layers of software to enable communication:

• the data-link layer

• the application layer

This figure shows how these layers fit together.

computer

application

common
application
routines

RS232
data link
layer

DH/DH+/DH485
RS232 interface modules

RS232 DH/DH+

link layer
(DF1)

link layer
(network)

DH485

PLC processor

application

common
application
routines

DH/DH+
/DH485 data
link layer

Datalink Layer

This layer controls the flow of communication over the physical link
and:

• determines the encoding of data on the physical medium

• controls who transmits data and who listens using an

arbitration protocol

• conveys data packets intact from the source node to the

destination node over the physical link

"

If your link is Then

you do not need to program this layer.

a DH, DH+ or DH485 link

a DF1 link between AllenBradley
interface modules

a DF1 link between an AllenBradley
interface module and a computer

Your application programs on the network
are not involved with internode protocol,
handshaking, or control of the link.

the interface modules automatically take
care of this layer. Your application
program does not have to be involved with
handshaking control.

you must program this layer at your
computer.

Programming the data-link layer

You can program the data link layer using DF1 protocol.
For more information, see Chapter 3, “Using Half-duplex Protocol to
Send and Receive Messages,” or Chapter 4, “Using Full-duplex
Protocol to Send and Receive Messages.”

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1–8 Network Layers

Application Layer

This layer controls and executes the actual commands specified in
the communication between nodes. This layer is the same for both
DF1 and network links. The application layer:

• interfaces to user processes and databases

• interprets commands

• formats user data into packets

The application layer depends upon the type of node the application
is running on since it must interface to the user process and interpret
the user database.

"

Processes in the application layer

The application layer is typically organized into two types of
processes:

• senders — A sender, after receiving a signal from the user

process, sends a message and awaits a reply. It then sends the
results to the user process.

• responders — A responder waits for an incoming message from

the link. When the responder receives a message, it performs the
indicated operation on the user data base and returns a reply
message to the sender.

If your physical link is Then

a network link

a DF1 link between AllenBradley interface
modules

1747KE

SLC 5/02

processor

the communication modules automatically
take care of this layer.

the interface modules automatically take
care of this layer. (See figure below.)

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DH485 link

RS232
DF1 fullduplex

a DF1 link between an AllenBradley
interface module and a computer

1785KE

PLC5/15
processor

DH+ link

you will need to program this layer at your
computer.

1–9Network Layers

Message Packet Structure

"

Messages

See Chapter 7, “Communication Commands,” for:

• a description of the command messages for each type of

PLC processor

• information on how to program the application layer fields of a

message packet for an asynchronous link

All messages on a network have the same fundamental structure,
regardless of their function or destination. If you could freeze a
message packet while it is in transmission, you would see:

Bytes Contents

Information used by the application and datalink layers of your software to
get the message to its destination:

protocol

data

•If a transaction originates from a PLC processor, the interface module

automatically fills the protocol bytes.

•If the transaction originates from a computer, your computer software

must supply the necessary protocol.

Information supplied by application program at the source and delivered to
the application program at the destination.

The following sections describe bytes that you define using the
application-layer protocol bytes in your message packet.
For a detailed description of how to use these bytes for each type of
command, see Chapter 7, “Communication Commands.”

To define this See this page

command and reply message 1-9

message priority 1-10

delivery order of commands 1-10

types of commands 1-11

error codes

1-11

Command and Reply Message

A network transaction consists of a command and a reply.
The two parts provide extra data integrity by making sure that a
required action always returns a reply with some sort of status, either
zero status for a good reply, or non-zero status as an error code.

The application-layer protocol distinguishes a command from a
reply. The data area of a command and its corresponding reply
depend on the type of command.

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1–10 Network Layers

Message Priority

You specify the priority level for each DH command in the message
command code. The node that receives a command message must
establish the same priority level for its corresponding reply message:

This link Classifies a message as

high priority or normal priority
Priority levels of messages determine the order in which nodes transmit

DH

DH+ normal priority

DH485 normal priority

Important: Nodes with high priority messages are given priority

messages on a DH link. In the polling process, nodes with high priority
messages will always be given priority over nodes with normal priority
messages.

over nodes with normal priority messages throughout
the command/reply message cycle. For this reason, a
command should be given a high priority designation
only when special handling of specific data is required.
Using an excessive number of high-priority commands
defeats the purpose of this feature and could delay or
inhibit the transmission of normal priority messages.

Delivery Order of Commands

The sending node, the network, and the receiving node execute
commands based on network conditions, including—but not limited
to:

• nodes buffering commands

• retries due to noise on the network

• priority levels

If your application requires that commands be delivered in a specific
order, your logic must control the initiation of one command at a
time on the network and verify delivery before initiating additional
commands. This verification is completed by:

• a done bit or an error bit in a PLC processor

• a reply message in a computer

A done bit or a successful reply causes the next command to be
initiated. If an error bit or a reply with non-zero status is returned,
you must decide the appropriate action based on your application.

Important: If any node on the network initiates multiple commands

(for example, the sending node sets multiple bits at any
one time), the order in which these commands get
executed at the receiving node cannot
be guaranteed.

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1–11Network Layers

Types of Commands

From your computer on a DF1 link to a node on a DH, DH+ or
DH485 link, you can send four types of commands:

• read

• write

• diagnostic

• upload/download

For additional information on the commands you can send,
see Chapter 7, “Communication Commands.”

Error Codes

When your computer sends a command on the asynchronous link, a
status code is returned in the reply message. This code tells you the
status of the command sent from your computer. You must program
your computer to interpret this code. For more information on codes
and their meanings, see Chapter 8, “Message Packet Status Codes.”

Error codes can be generated at two places:

• the sending node

• the receiving node

For codes that are returned from the sending node:

From this node Error codes are generated when

•an application program used the wrong message format or issued

sending node

receiving node

illegal commands.

•the sending node cannot complete a transaction due to network

problems.

an application problem exists at the receiving node. Typically, these
involve:

•the PLC processor being off line (in Program mode, for example)

or

•the command trying to access a memory area is blocked by the

interface module or user application program (i.e., the data table
location does not exist or is restricted).

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Protocol

Understanding DF1 Protocol  Chapter 2

Using Halfduplex Protocols to Send and Receive
Messages  Chapter 3

Using Fullduplex Protocols to Send and Receive
Messages  Chapter 4

Chapter 2

Understanding DF1 Protocol

If you are connecting an interface module to a computer, you must
program the computer to understand and issue the proper protocol
character sequences. This chapter describes the DF1 protocol you
can use with your DF1-link driver for:

• peer-to-peer (two-way simultaneous) communication

• master-slave (two-way alternate) communication

This chapter includes these sections:

Section Page

DF1 Protocol 2-2

Character Transmission 2-5

Transmission Symbols

Important: The 1784-KT and 1784-KT2 cards connect directly to

DH+; the 1784-KR card connects directly to DH-485.
As a result, an asynchronous RS-232 interface is not
used and the information in this chapter does not apply
to software written for these cards, which use the
Standard Driver software.

2-6

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2–2 Understanding DF1 Protocol

DF1 Protocol

A link protocol is a set of programming rules for interpreting the
signals transmitted over a physical link. A protocol, such as DF1:

• carries a message, error free, from one end of the link to the other

It has no concern for the content of the message, the function of
the message, or the ultimate purpose of the message.

For example, with full-duplex DF1 protocol, it accomplishes this
by attaching a check character (BCC) or check characters (CRC)
to the end of each command and reply. The device receiving the
command or reply then verifies the BCC or CRC and returns an
ACK—if the BCC or CRC is acceptable—or an NAK—if the
BCC or CRC does not check.

• indicates failure with an error code

Internally, the link protocol must delimit messages, detect and
signal errors, retry after errors, and control message flow.

DF1 protocol is an Allen-Bradley data-link layer protocol that
combines features of subcategories D1 (data transparency) and F1
(two-way simultaneous transmission with embedded responses) of
ANSI x3.28 specification. There are two categories of DF1
protocol:

• half-duplex protocol (master-slave communication)

• full-duplex protocol (peer-to-peer communication)

Halfduplex Protocol

Half-duplex protocol is a multidrop protocol for one master and one
or more slaves. With half-duplex protocol, you can have 2 to 255
nodes simultaneously connected on a single link; this link operates
with all nodes interfaced through half-duplex modems. (For a list of
devices that can be used as masters and slaves, see page 3–2. For
more on half-duplex protocol, refer to Chapter 3, “Using Half-duplex
Protocol to Send and Receive Messages.”)

To implement half-duplex protocol, use the following
communication characteristics:

• 8 bits per character

• no parity

• 1 stop bit

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2–3Understanding DF1 Protocol

"

Using half-duplex protocol

When you use half-duplex protocol, the intended environment is a
multidrop link with all nodes interfaced through half-duplex
modems. Unless there is only one slave directly connected to a
master, you must use a modem. Your modems must support these
signals:

• request-to-send (RTS)

• clear-to-send (CTS)

• data-carrier-detect (DCD)

• data-set-ready (DSR)

• data-terminal-ready (DTR)

If your modem does not support the DCD and DSR signals, you
must jumper DCD and DSR to DTR.

You designate one node as master to control which node has access
to the link. All other nodes are slaves, and must wait for permission
from the master before transmitting. Each slave node has a unique
node number between 0 and 254 (decimal).

"

The master can send and receive messages to and from each node on
the multidrop link and to and from every node on network links
connected to the multidrop link.

If the master is programmed to relay messages, then nodes on the
multidrop link can engage in virtual slave-to-slave communication.
This communication is transparent to the application.

Multiple masters are not allowed, except when one acts as a
backup to the other and does not communicate unless the primary is
shut down.

Slave-to-slave communication

In slave-to-slave communication, the master looks at the packet
received from the slave. If the packet is not for the master,
the master reassembles the packet as a master packet and sends the
packet to slave devices.

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2–4 Understanding DF1 Protocol

Fullduplex Protocol

Use full-duplex protocol:

• over a point-to-point link that allows two-way simultaneous

transmission

• over a multidrop link where interface modules are able to

arbitrate transmission on the link

• for high performance applications where it is necessary to get the

highest possible throughput from the available medium

If you connect an interface module to another Allen-Bradley
communication interface module, the modules automatically handle
the link arbitration. (For a list of modules that automatically handle
link arbitration, refer to page 4–1.)

"

Full-duplex dial-up modems

Full-duplex dial-up modems can be used as long as a carrier is
detected before the carrier timeout (about 10 seconds). If a carrier is
not sensed before the timeout, the module drops DTR to trigger the
modem to hang up the phone. A carrier must be sensed at least
every 10 seconds to maintain the connection.

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2–5Understanding DF1 Protocol

Character Transmission

Allen-Bradley interface modules send data serially over the
RS-232-C/RS-422-A interface, one 10-bit byte—11-bit byte with
parity—at a time. The transmission format conforms to ANSI
X3.16, CCITT V.4, and ISO 1177 standards, with the exception that
the parity bit is retained while the data length is extended to eight
bits. Make sure that your computer conforms to this mode of
transmission. The transmission format is:

No Parity

start bit
data bit 0
data bit 1
data bit 2
data bit 3
data bit 4
data bit 5
data bit 6
data bit 7
one stop bit

With Parity

start bit
data bit 0
data bit 1
data bit 2
data bit 3
data bit 4
data bit 5
data bit 6
data bit 7
even parity bit
one stop bit

For all DH, DH+, and DH485 interface modules, you must comply
with this transmission format. For communication rates and parity
settings, refer to your module’s user manual.

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2–6 Understanding DF1 Protocol

Transmission Symbols

Both half-duplex and full-duplex protocols are character-oriented.
They use the ASCII control characters in the tables below, extended
to eight bits by adding a zero for bit 7:

Table 2.A
Halfduplex Protocol

Abbreviation

STX 02 0000 0010

SOH 01 0000 0001

ETX 03 0000 0011

EOT 04 0000 0100

ENQ 05 0000 0101

ACK 06 0000 0110

DLE 10 0001 0000

NAK 0F 0000 1111

Table 2.B
Fullduplex Protocol

Abbreviation

STX 02 0000 0010

ETX 03 0000 0011

ENQ 05 0000 0101

ACK 06 0000 0110

DLE 10 0001 0000

NAK 0F 0000 1111

Hexadecimal Value Binary Value

Hexadecimal Value Binary Value

(For the standard definition of these characters, refer to the ANSI
X3.4, CCITT V.3, and ISO 646 standards.)

A symbol is a sequence of one or more bytes having a specific
meaning to the link protocol. The component characters of a
symbol must be sent one after another with no other characters
between them. DF1 protocol combines the characters listed in the
tables above into control and data symbols:

• Control symbols are fixed symbols required by the DF1 protocol

to read a particular message

• Data symbols are variable symbols which contain the application

data for a particular message

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Table 2.C
Halfduplex Transmission Symbols

2–7Understanding DF1 Protocol

Symbol

Type Meaning

DLE SOH control symbol

DLE STX control symbol

DLE ETX
BCC/CRC

control symbol Sender symbol that terminates a message.

DLE ACK control symbol

DLE NAK control symbol

DLE ENQ control symbol

DLE EOT
BCC

control symbol

STN data symbol

APP DATA data symbol

DLE DLE data symbol

Sender symbol that indicates the start of a master
message.

Sender symbol that separates the multidrop
header from the data.

Response symbol which signals that a message
has been successfully received.

Global link reset command only issued by the
master. Causes the slaves to cancel all messages
that are ready to transmit to the master. Typically,
the slave returns the message and an error code to
the originator.

Sender symbol, issued only by the master, that
starts a poll command.

Response symbol used by slaves as a response to
a poll when they have no messages to send.

Station number of the slave node on your
halfduplex link.

Single characters having values 000F and 11FF.
Includes data from application layer including user
programs and common application routines. A data

is sent as 10 10 (DLE DLE).

10

16

Represents the data value or STN value
of 10

. See APP DATA.

16

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2–8 Understanding DF1 Protocol

Table 2.D
Fullduplex Transmission Symbols

Symbol

DLE STX control symbol

DLE ETX
BCC/CRC

DLE ACK control symbol

DLE NAK control symbol

DLE ENQ control symbol

Type Meaning

Sender symbol that indicates the start of a message
frame.

control symbol Sender symbol that terminates a message frame.

Response symbol which signals that a message
frame has been successfully received.

Response symbol which signals that a message
frame was not received successfully.

Sender symbol that requests retransmission of a
response symbol from the receiver.

Single character data values between 000F and

APP DATA data symbol

11FF. Includes data from application layer including
user programs and common application routines.
A data 10

is sent as 10 10 (DLE DLE).

16

DLE DLE data symbol Represents the data value of 1016.

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Chapter 3

Using Halfduplex Protocols to
Send and Receive Messages

In half-duplex protocol, devices share the same data circuits,
therefore only one device can “talk” at a time. Half-duplex protocol
can be likened to a one-lane bridge: each car must wait its turn to
cross the bridge. (To compare half-duplex to full-duplex protocol,
refer to Chapter 4, “Using Full-duplex Protocols to Send and
Receive Messages.”)

Read this chapter to help learn how to use half-duplex protocol to
send and receive messages. It contains these sections:

Section Page

Halfduplex Protocol Message Transmission 3-2

Transmitter and Receiver Message Transfer 3-3

Halfduplex Protocol Environment 3-3

Message Characteristics 3-7

Master Polling Responsibilities 3-7

Slave Transceiver Actions 3-9

Halfduplex Protocol Diagrams

3-11

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3–2 Using Half-duplex Protocols to Send and Receive Messages

Halfduplex Protocol Message
Transmission

Half-duplex protocol:

• is a multidrop protocol for one master and one or more slaves

• provides a lower data throughput than full-duplex

• allows communication with each node on the multidrop link

• allows communication with nodes on links connected to the

multidrop link

If the master is programmed to relay messages, then nodes on the
multidrop can engage in virtual slave-to-slave transfers. Half-duplex
protocol operates on a multidrop link with all nodes interfaced
through half-duplex modems. There may be from 2 to 255 nodes
simultaneously connected to a single link.

In half-duplex mode, one node is designated as master and it
controls which node has access to the link. All other nodes are
called slaves and must wait for permission from the master before
transmitting. Allen-Bradley devices with master and slave
capabilities include:

Devices with master capability Devices with slave capability

•SLC 5/03 and 5/04 (on channel 0)

•1771KGM DH SCADA Master module •1770KF2, KF3, KFC

•5130RM1, RM2, KA (channel 1) •1775KA (via modem port)

•5130RM2 •1785KE

•a userprogrammed intelligent device •1771KE, KF, KG

•a personal computer running ControlView

software

•PLC5/11 5/20, 5/30, 5/40, 5/60,

PLC5/80 (on channel 0)

•personal computer running

WINtelligentt LINXt software

•personal computer running RSLINXt

À

SLC 5/03 and 5/04 processors (OS302 and OS401, respectively) now support halfduplex DF1
masters.

À

•1747KE

•PLC5/11 5/20, 5/30, 5/40, 5/60,

PLC5/80 (on channel 0)

•SLC 5/03 and 5/04 (on channel 0)

•5130RM1, RM2, KA (channel 1)

•personal computer running

WINtelligentt LINXt software

•personal computer running RSLINXt

Publication

With half-duplex protocol, you can use a:

• two-circuit system – master sends and slaves receive on one

circuit, slaves send and master receives on the other

• one-circuit system – master and slaves send and receive on the

same circuit

17706.5.16 - October 1996

3–3Using Half-duplex Protocols to Send and Receive Messages

Transmitter and Receiver Message Transfer

Each node on a multidrop link contains a software routine to transmit
and receive messages. DH and DH+ interface modules already
contain a slave transceiver routine, so they can be configured to
function as slave nodes in half-duplex mode.

Instead of a single routine, you can program separate transmitter and
receiver routines. However, in this chapter, we assume you are using
a single routine. The master and slave transmitter/receivers are
illustrated in the figure below:

source

sink

packet

OK

packet

OK

master transceiver

physical linkto other slaves

packet

OK

source

Halfduplex Protocol
Environment

slave transceiver

packet

OK

sink

(The “source” and “sink” are defined in the next section,
“Half-duplex Protocol Environment.”

To define the environment of the protocol, the transceiver:

• needs to know where to get the message it sends, the message

source. We assume the message source:

– supplies one message at a time upon request from the

transceiver

– requires notification of the success or failure of the transfer

before supplying the next message

• must have a means of disposing of messages it receives, the

message sink

When the transceiver has received a message successfully, it attempts
to give it to the message sink. If the message sink is full,
the transceiver will receive an indication that the sink is full.

Publication

17706.5.16 - October 1996

3–4 Using Half-duplex Protocols to Send and Receive Messages

The following program describes the actions of the transceiver in
detail:

TRANSCEIVER

variables

LAST-HEADER = invalid
loop

is defined

LAST

-HEADER is 4 bytes copied out of the last good message

BCC is an 8-bit block check accumulator

reset parity error flag
GET-CODE
if it’

s a DLE SOH then

begin

end

else if it’

begin

end

else if it’

send a success code to the message source and discard the
message

else if it’

while the message source can supply a message

end

GET-CODE
if it’

s a data code and it matches the station number or it

is 255 (the broadcast address) then

begin

BCC = the data code
GET-CODE
if it’

s a DLE STX then

begin

RESPONSE = GETMESSAGE
if RESPONSE is ACK then

begin

if message header is dif
last and sink is not full

begin

save new HEADER
try to send message to sink

end
if this is not a broadcast message
and sink was not full then

begin

turn on R
wait for CTS
send DLE ACK
turn of

end

s a DLE ENQ then

GET

-CODE (the station number)
GET-CHAR (the BCC)
check the station number and the BCC, and if they’re OK then

begin
if there is a message left over from the last time and
the transmit counter is exceeded then

if there is no message then
turn on R

wait for CTS
if there is still no message then send a DLE EOT
else SEND the message
turn of
end

s a DLE ACK then

s a DLE NAK then

begin

get a message from the message source
discard the message
send an error code to the message source

end

end

throw the message away and send an error code to the
message source

try to get one from the message source

TS

f RTS

end

end

ferent from

TS

f RTS

Publication

17706.5.16 - October 1996

3–5Using Half-duplex Protocols to Send and Receive Messages

GETMESSAGE

GET-CODE
while it is data code

if it is a control code and it is an ETX then

else end

GET-CODE is defined as

loop

end

is defined as

begin

if buf

fer is not overflowed put data in buf

GET-CODE

end
begin

if parity error flag is set then return a NAK
if BCC is not zero then return a NAK
if message is too small then return a NAK
if message is too large then return a NAK
return an ACK

end

variable
GET-CHAR
if char is not a DLE

begin

add char to BCC
return the char and a data flag

end

else

begin

GET-CHAR
if char is a DLE

begin

add char to BCC
return a DLE and a data flag

end

else if char is an ETX

else return char with a control flag

end

end

begin

GET-CHAR
add char to BCC
return ETX with a control flag

end

fer

GETCHAR is defined as

an implementationdependent function that returns one byte of data
from the link interface hardware

SEND (Message) is defined as

begin

BCC = 0
send DLE STX
for every byte in the message do

begin

subtract the byte from the BCC
send the corresponding data code

end

send DLE ETX BCC

end

Publication

17706.5.16 - October 1996

3–6 Using Half-duplex Protocols to Send and Receive Messages

The following flowchart shows the software logic for implementing
half-duplex protocol from the master node’s point of view:

XCVR

Yes

Yes

Does master
have message
to send?

No

Select node

Send poll

Start timeout

Receive
DLE
EOT?

Yes

Node
in active
list?

No

Add node to
active list

No Yes

Receive
message?

No Yes

No

Active
node?

Yes

Message
OK?

Duplicate
message?

No

Send message to
application layer

No

Yes

Send DLE ACK

Get message from
application layer

Send message

Start timeout

Yes

Received
DLE
ACK?

3
timeouts
this
message?

No

No

Yes

3
timeouts
this poll?

Yes

Tell application
layer of failure

Add node to
inactive list

Send DLE ACK

No

Publication

17706.5.16 - October 1996

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Chapter 4

Using Fullduplex Protocol to
Send and Receive Messages

In full-duplex protocol, devices share the same data circuits, and
both devices can “talk” at the same time. Full-duplex protocol can
be likened to a two-lane bridge: traffic can travel in both directions
at one time. (To compare full-duplex to half-duplex protocol, refer
to Chapter 3, “Using Half-duplex Protocols to Send and Receive
Messages.”)

Read this chapter to help learn how to use full-duplex protocol to
send and receive messages. It contains these sections:

Section Page

Fullduplex Protocol Message Transmission 4-2

Fullduplex Protocol Environment 4-3

Message Characteristics 4-4

Transmitter and Receiver Message Transfer 4-4

Fullduplex Protocol Diagrams

4-10

"

Link arbitration

You can use these Allen-Bradley interface modules to automatically
handle the link arbitration:

•1747KE •1771KE •1775KA (via modem port)

•1770KF2 •1771KF •1785KE

•1770KF3 •1771KG •5130RM1 (channel one)

•1770KFC • 5130KA •5130RM2

Publication

17706.5.16 - October 1996

4–2 Using Full-duplex Protocol to Send and Receive Messages

Fullduplex Protocol
Message Transmission

circuit 1

circuit 2

With full-duplex protocol, a link uses two physical circuits for
two-way simultaneous message transmission (command or reply
message packets). These two physical circuits provide
communication on four logical paths:

Figure 4.1
Data paths for twoway simultaneous operation

path 1

transmitter A

path 2

path 3

path 4

•On the first circuit, transmitter A sends messages to receiver B (path 1) and receiver A sends response

control symbols (DLE ACK, DLE NAK) to transmitter B (path 3).

•On the second circuit, transmitter B sends messages to receiver A (path 4) and receiver B sends

response control symbols (DLE ACK, DLE NAK) to transmitter A (path 2).

•All message and symbols on the first circuit are traveling in the same direction (node A to node B) and all

messages and symbols on the second circuit are traveling in the opposite direction (B to A).

receiver B

transmitter Breceiver A

Publication

17706.5.16 - October 1996

Figure 4.2
Software implementation of data paths

Paths 1, 2, 3, and 4

4–3Using Full-duplex Protocol to Send and Receive Messages

Transmitter A

Path 2

Software
Separator

Receiver A

Paths 1 (a message symbol sent from node A to node B)

•To implement four logical paths with two physical circuits, a software multiplexer is needed to combine the message symbols with

the response symbols going in the same direction.

•At the other end of the link, a software separator divides the message symbols from the response symbols.

The internal software sends the message symbols to the appropriate receiver, and the response symbols to the appropriate
transmitter.

•Although message symbols and response symbols on the same circuit operate independently of each other,

there is some interaction.

•For example, a message on physical circuit AB will be delayed if a response symbol from receiver A is inserted in a stream of

message symbols from transmitter A (embedded response).

•Also, any hardware problems that affect message symbols traveling over a circuit will also affect response symbols

on the same circuit.

Path 1

Software
Multiplexer

Physical Circuit BA

Path 3 Path 4Path 4 Path 3

Transmitter A

Path 1

Software
Multiplexer

Physical Circuit AB

Physical Circuit

Receiver B

Path 2

Software
Multiplexer

Transmitter B

Path 1

Software
Separator

Receiver B

Path 1

Software
Separator

Fullduplex Protocol
Environment

To define the environment of the protocol:

• the transmitter needs to know where to get the message it sends,

the message source. We assume the message source:

– supplies one message at a time upon request from the

transmitter

– requires notification of the success or failure of the transfer

before supplying the next message

• the receiver must have a means of disposing of messages,

the message sink

If the Then the

message source is empty

receiver has received a message
successfully

transmitter waits in an inactive state until a
message is available

receiver attempts to give it to the message
sink. If the message sink is full, the
receiver must be notified

Publication

17706.5.16 - October 1996

4–4 Using Full-duplex Protocol to Send and Receive Messages

Figure 4.3 shows the protocol environment for message symbols
from transmitter A to receiver B (path 1) and response codes from
receiver B to transmitter A (path 2).

Figure 4.3
Protocol Environment

Packet

Transmitter A SinkReceiver BSource

Path 1

Path 2

Packet

Sink FullPacket Status

Message Characteristics

Ideally, the data-link-layer protocol is not concerned with the content

or form of the message packet (link-layer data) it is transferring.
However, full-duplex protocol places the following restrictions on
link-layer data submitted to it for transfer:

• minimum size of valid link-layer data is 6 bytes

• maximum size of valid link-layer data depends on the

application-layer command

• some protocol implementations (e.g., point-to-point links to a

1771-KG module) require that the first byte of the link-layer data
match the node address

The receiver ignores messages that do not contain the correct
address.

• as part of the duplicate message detection algorithm, the receiver

compares the second, third, fifth, and sixth bytes of the link-layer
data with the same bytes in the previous message

If there is no difference between the sets of bytes, the message is
classified as a re-transmission of the previous message. You can
set some Allen-Bradley interface modules so that they do not
implement duplicate-message detection.

Transmitter and Receiver
Message

Publication

Transfer

17706.5.16 - October 1996

In full-duplex protocol, messages are sent from the source (part of
software that supplies message packet) through a transmitter
(device that sends data) and then a receiver (device that receives
data) to the sink (part of the software that accepts the received data):

For See page

structured text on how the transmitter operates 4-5

a flowchart of how the transmitter operates 4-6

structured text on how the receiver operates 4-7

a flowchart of how the receiver operates

4-9

How the Transmitter Operates

The following program describes the actions of the transmitter:

Whenever the message source can supply a message packet and the
transmitter is not busy
address. It then starts a timeout, and waits for a response.

When this response is The message packet
received from the receiving
address

DLE ACK

DLE NAK

If the timeout expires before a response is received, the transmitter sends
a DLE ENQ to request a retransmission of the last response. It restarts
the timeout and waits for a response.

Y

ou can also set a limit to the number of timeouts that are allowed per
message. If the enquiry (ENQ) limit is exceeded, the transmitter signals
the message source that the transmission has failed, and the transmitter
proceeds to the next message.

There are three responses defined: DLE ACK, DLE NAK, DLE ENQ,
If the transmitter receives an different response, the transmitter ignores it.

, it sends a frame on the link to the destination

has been successfully transferred.
After signaling the message
source that the message packet
was successfully transmitted, the
transmitter proceeds with the next
message packet.

is retransmitted. The transmitter
restarts the timeout and waits
again for a response. If it receives
a DLE ACK, the transmitter starts
a timeout.

This can be repeated several
times. You can set a limit to the
number of times a message can
be retransmitted for each module.
If this limit is exceeded, the
message source is informed of the
failure and the transmitter
proceeds with the next message.

TRANSMITTER is defined as

loop

Message=GET-MESSAGE-TO-SEND
Status=TRANSFER(Message)
SIGNAL-RESULTS(Status)

end loop
loop
WAIT for response on path 2 or timeout.
if received DLE ACK then return SUCCESS
else if received DLE NAK then

if nak-limit is exceeded then return FAILURE

else

begin

count NAK re-tries;
SEND-MESSAGE(message);
start timeout

end

else if timeout

if enq-limit is exceeded then return FAILURE

else

begin

count ENQ re-tries;
send DLE ENQ on path 1;
start timeout

end

end loop
SEND (message) is defined as

begin

BCC = 0
send DLE STX on path 1
for every byte in the message do

begin

add the byte to the BCC;
send the corresponding data symbol

on

path 1

end

send DLE ETX BCC on path 1

end
GET-MESSAGE-TO-SEND

This is an operating-system-dependent interface

routine that waits and allows the rest of the

system to run until the message source has supplied

a message to be sent.
SIGNAL-RESULTS

This is an implementation-dependent routine that

tells the message source of the results of the

attempted message transfer.
WAIT

This is an operating-system-dependent routine

that waits for any of several events to occur

while allowing other parts of the system to run.
TRANSFER (Message) is defined as

initialize nak-limit and enq-limit

SEND(Message)

start timeout

4–5Using Full-duplex Protocol to Send and Receive Messages

Publication

17706.5.16 - October 1996

4–6 Using Full-duplex Protocol to Send and Receive Messages

The following flowcharts the software logic for implementing the
transmitter:

Legend:

= Ready to transmit next message

T

= Recovery procedure

P

= Default values used by the module

*

T

message frame

DataDLE STX DLE ETX

Received
DLE
ACK?

No No

Yes Ye s Yes

T

retransmit same message

BCC/CRC

Field

timeout loop

Received
DLE
NAK?

3* NAKs
received
for this
message?

Yes Yes

P

No No

Timed
out?

3* ENQ
sent?

DLE ENQ

No

Important: Depending on network-link traffic and saturation level,

you may need to wait for a reply from the remote node
before transmitting the next message. Implement an
option that allows users to choose the maximum amount
of outstanding messages that can exist at one time;
we suggest a selectable range of one to three messages.

Publication

17706.5.16 - October 1996

4–7Using Full-duplex Protocol to Send and Receive Messages

How the Receiver Operates

The receiver must be capable of responding to adverse situations.
Some of the problems that can occur are:

• the message sink is full, so the receiver has nowhere to put

a message

• a message can contain a parity error

• the BCC or CRC can be invalid

• the DLE STX or DLE ETX BCC/CRC may be missing

• the message is too long or too short

• a false control or data symbol occurs outside a message

• a false control symbol occurs inside a message

• the DLE ACK response is lost, causing the transmitter to send a

duplicate copy of a message already passed to the message sink

Publication

17706.5.16 - October 1996

4–8 Using Full-duplex Protocol to Send and Receive Messages

The following program describes the actions of the receiver in detail.

The receiver keeps a record of the last response sent to
the transmitter
ACK or DLE NAK. It is initialized to DLE NAK. When a
DLE ENQ (enquiry) is received from the transmitter
receiver sends the value of the last response.

The receiver ignores all input until a DLE STX or DLE ENQ
is received. If anything other than a DLE STX or DLE ENQ
is received on path one, the receiver sets the last response
variable to NAK.

When this symbol is received Then the
from the transmitter

DLE ENQ

DLE ACK

While building a reply message, all data symbols are
stored in the message buf
If the buf
BCC/CRC, but the data is discarded.

If a parity, overrun, framing, or modem handshaking error is
detected, it is recorded .

If a control symbol other than DLE STX or DLE ETX is
received, the message is aborted and a DLE NAK is sent
to the transmitter
the error flag, the BCC/CRC, the message size, and the
address (optionally) are all checked. If any of the tests fail,
a DLE NAK is sent.

GET
function that returns one byte of data from the link
interface hardware

. The value of this response is either DLE

, the

last response is sent
and the receiver
continues waiting for
input.

BCC/CRC and the
message buf
reset, and the receiver
starts building a reply
message.

fer and added to the BCC/CRC.

fer overflows, the receiver continues summing the

. When DLE STX or DLE ETX is received,

CHAR is defined as an implementationdependant

fer are

RECEIVER

GET

end
else return char with a control flag

is defined as

variables

LAST

-HEADER is 4 bytes copied out of the last good message
RESPONSE is the value of the last ACK or NAK sent
BCC is an 8-bit block check accumulator

LAST-HEADER = invalid
LAST RESPONSE = NAK
loop

reset parity error flag
GET-SYMBOL
if DLE STX then

begin

BCC = 0
GET-SYMBOL
while it is a data symbol

begin

if buf
data in buf
GET-SYMBOL

end
if the control symbol is not a DLE ETX then send DLE
NAK
else if error flag is set then send DLE NAK
else if BCC is not zero then send DLE NAK
else if message is too small then send DLE NAK
else if message is too large then send DLE NAK
else if header is same as last message send a DLE ACK
else if message sink is full send DLE NAK
else

begin

send message to message sink
send a DLE ACK
save a last header

end

else if DLE ENQ then send LAST
else LAST

end loop

-SYMBOL is defined as
loop

GET-CHAR
if char is not DLE

else

GET-CHAR
add char to BCC
return ETX with a control flag

end loop

end

-RESPONSE = NAK

begin

add char to BCC
return the char and data flag

end

begin

GET-CHAR
if char is a DLE

begin

add char to BCC
return DLE and data flag

end

else if char is an ACK or NAK send it to the transmitter
else if char is an ETX

begin

end

fer is not overflowed put

fer

-RESPONSE

Publication

17706.5.16 - October 1996

The following flowchart is the software logic for implementing the
receiver.

RCVE

LAST = NAK

4–9Using Full-duplex Protocol to Send and Receive Messages

No

Received
DLE
ENQ?

No

Received
message?

Yes

BCC/
CRC
OK?

Yes

LAST = ACK

Yes

No

LAST = NAK

Send DLE LAST

Publication

17706.5.16 - October 1996

4–10 Using Full-duplex Protocol to Send and Receive Messages

Fullduplex Protocol
Diagrams

These transfer diagrams show events that occur on various
interfaces. Time is represented as increasing from the top of the
diagram to the bottom. Link-layer data bytes are represented by
“xxxx” and corrupted data by “???”.

For this diagram See page

normal message transfer 4-10

message transfer with NAK 4-11

message transfer with timeout & ENQ 4-12

message transfer with retransmission 4-13

message transfer with message sink full 4-14

message transfer with NAK on reply 4-15

message transfer with timeout and ENQ for the reply 4-16

message transfer with message source full on the reply

4-17

Normal Message Transfer

In this transfer:

• the transmitter sends the data to the receiver

• the sink sends a “not full” message

• the receiver sends the data to the sink and sends a DLE ACK to

the transmitter

• the transmitter tells the source that the data was delivered

• reply is successfully returned

Source Transmitter Link Receiver Sink

command

reply

xxxx

OK

(sometime later ...)

not full

xxxx

DLE STX xxxx DLE ETX BCC/CRC

not full
xxxx

DLE ACK

DLE STX xxxx DLE ETX BCC/CRC

DLE ACK

OK

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4–11Using Full-duplex Protocol to Send and Receive Messages

Message Transfer with NAK

In this transfer:

• the transmitter sends corrupted data to the receiver and the

receiver responds with a DLE NAK

• the transmitter retransmits and the transmission is successful

• the receiver sends a DLE ACK to the transmitter

• reply is successfully returned

Source Transmitter Link Receiver Sink

command

xxxx

OK

DLE STX x???x DLE ETX BCC/CRC

DLE NAK

DLE STX xxxx DLE ETX BCC/CRC

not full
xxxx

DLE ACK

reply

(sometime later ...)

DLE STX xxxx DLE ETX BCC/CRC

not full

xxxx

DLE ACK

OK

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4–12 Using Full-duplex Protocol to Send and Receive Messages

Message Transfer with Timeout and ENQ

In this transfer:

• the receiver receives a transmission, but sends back a

DLE ACK that is corrupted

• the transmitter times out waiting for the DLE ACK and sends a

DLE ENQ

• the receiver sends back a DLE ACK

• a reply is successfully returned

Source Transmitter Link Receiver Sink

command

xxxx

DLE STX xxxx DLE ETX BCC/CRC

(timeout)

OK

(sometime later ...)

reply

DLE STX xxxx DLE ETX BCC/CRC

not full

xxxx

not full

xxxx

DL???CK

DLE ENQ
DLE ACK

DLE ACK

OK

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4–13Using Full-duplex Protocol to Send and Receive Messages

Message Transfer with ReTransmission

In this transfer:

• noise destroys the DLE ACK while also producing invalid

characters at the receiver

• because of the invalid characters, the receiver changes its last

response variable to a DLE NAK

• since the DLE ACK was destroyed, the transmitter sends a DLE

ENQ (enquiry), and the receiver returns the DLE NAK

• the transmitter retransmits the message and the receiver sends an

ACK

• the receiver discards the duplicate message (if duplicate message

detection is enabled on your module)

• reply is successfully returned

Source Transmitter Link Receiver Sink

command

xxxx

(timeout)

(timeout)

DLE STX xxxx DLE ETX BCC/CRC

not full

xxxx

DL???CK

???

DLE ENQ

DLE NAK

reply

OK

(sometime later ...)

not full

xxxx

DLE STX xxxx DLE ETX BCC/CRC

DLE ACK

DLE STX xxxx DLE ETX BCC/CRC

DLE ACK

(duplicate message)

In this transfer, the receiver has no way of knowing that the DLE
ACK it sent to the transmitter was destroyed. If the transmitter’s
ACK timeout is large enough, it is possible that the reply
(i.e., DLE STX xxxx DLE ETX BCC/CRC) comes back before the
transmitter sends the DLE ENQ. Therefore, the reply comes in
before the DLE ACK is received by the transmitter.

OK

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4–14 Using Full-duplex Protocol to Send and Receive Messages

Message Transfer with Message Sink Full

In this transfer:

• the transmitter sends a message but the message sink is full,

so the receiver sends back a DLE NAK

• the transmitter retransmits and the sink is no longer full,

so the receiver returns a DLE ACK

• a reply is successfully returned

Source Transmitter Link Receiver Sink

command

xxxx

OK

(sometime later ...)

reply

not full

xxxx

DLE STX xxxx DLE ETX BCC/CRC

DLE STX xxxx DLE ETX BCC/CRC

DLE STX xxxx DLE ETX BCC/CRC

DLE STX xxxx DLE ETX BCC/CRC

Full

DLE NAK

Full

DLE NAK

not full
xxxx

DLE ACK

DLE ACK

OK

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4–15Using Full-duplex Protocol to Send and Receive Messages

Message Transfer with NAK on Reply

In this transfer:

• the message is successfully transmitted on the network

• the reply is corrupted and the transmitter responds with a DLE

NAK

• the reply is sent again and is successful

Source Transmitter Link Receiver Sink

command

xxxx

OK

(sometime later ...)

reply

not full

xxxx

DLE STX xxxx DLE ETX BCC/CRC

DLE ACK

DLE STX x??x DLE ETX BCC/CRC

DLE NAK

DLE STX xxxx DLE ETX BCC/CRC

DLE ACK

not full

xxxx

OK

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4–16 Using Full-duplex Protocol to Send and Receive Messages

Message Transfer with Timeout and ENQ for the Reply

In this transfer:

• the message is successfully transmitted on the network

• the receiver sends a reply from the network but the transmitter

sends back a DLE ACK that is corrupted

• the receiver times out waiting for the DLE ACK and sends a DLE

ENQ

• the transmitter sends back a DLE ACK

Source Transmitter Link Receiver Sink

command

xxxx

DLE STX xxxx DLE ETX BCC/CRC

OK

(sometime later ...)

DLE ACK

not full

xxxx

reply

DLE STX xxxx DLE ETX BCC/CRC

not full

xxxx

DL???CK

(Timeout)

DLE ENQ

DLE ACK

OK

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Message Transfer with Message Source Full on the Reply

In this transfer:

• the message is successfully transmitted on the network

• the receiver sends a reply but the message source is full,

so the transmitter sends back a DLE NAK

• the receiver retransmits and the source is no longer full,

so the transmitter returns a DLE ACK

Source Transmitter Link Receiver Sink

command

reply

xxxx

OK

(sometime later ...)

Full

DLE STX xxxx DLE ETX BCC/CRC

DLE ACK

DLE STX xxxx DLE ETX BCC/CRC

not full
xxxx

4–17Using Full-duplex Protocol to Send and Receive Messages

not full

xxxx

DLE NAK

DLE STX xxxx DLE ETX BCC/CRC

DLE ACK

OK

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Message Packets

Datalink Layer Message Frames  Chapter 5

Application Layer Message Packets  Chapter 6

Communication Commands  Chapter 7

Message Packet Status Codes (STS and EXT STS)
 Chapter 8

Chapter 5

Datalink Layer Message
Frames

In the data-link layer of a message frame:

• half-duplex protocol uses three types of message transmission

• full-duplex protocol implements its message fields at different

network layers

• at the end of each polling and message frame, there is a one-byte

BCC field or a two-byte CRC field

Read this chapter to help learn the fields that your computer uses in
the data-link layer of a message frame. It contains these sections:

Section Page

Halfduplex Protocol Message Frames 5-2

Fullduplex Protocol Message Frames 5-3

BCC and CRC Fields

5-4

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5–2 Data-link Layer Message Frames

Halfduplex Protocol
Message Frames

Half-duplex protocol uses three types of transmissions:

• polling frame

• master message frame

• slave message frame

The master node transmits both polling frames and master message
frames, and slave nodes transmit slave message frames.
The following figure illustrates the formats of these frames.
The slave message frame has the same format as the full-duplex
message frame. The master message frame is the same as the slave
message frame except that it is prefixed with DLE SOH and an
address to specify a slave station address (STN).

Important: Even if you set your module to use CRC, when you

send a polling frame, it uses a single BCC byte.

Polling Frame

BCCENQDLE STN

Master Message Frame

From common application routines

CMD STSSRC TNSDLE DSTSTXDLE SOH STN

Data
(command

data)

DLE ETX

BCC/

CRC

Slave Message Frame

CMD STSSRC TNSDLE DSTSTX

From common application routines

The BCC field contains the 2's complement of the 8bit sum (module256 arithmetic sum) of the slave station address
(STN) and all the data bytes in the frame. For polling frames, the BCC is simply the 2's complement of STN. The BCC
does not include any other message frame symbols or response symbols.

Data
(command data)

DLE ETX

BCC/

CRC

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5–3Data-link Layer Message Frames

Fullduplex Protocol
Message Frames

From user application program

From common application routines

Datalink layer frame

Full-duplex protocol implements different message frames,
depending on the network layer. This figure shows the format of a
message frame for full-duplex protocol and the layer at which each
portion is implemented:

DST CMD STS

DST CMD STSSRC

DLE STX DLE ETX

The

BCC/CRC field contains the 2'
application layer data bytes between the DLE STX and the DLE ETX BCC. It does not include any
response symbols. Y

• block check character (BCC)

• 16bit cyclic redundancy check (CRC16)

data from
application layers

ou can use the BCC/CRC field for one of the following types of error checking:

TNS

s complement of the 8bit sum (module256 arithmetic sum) of all

command data

data
(from application layer)

BCC/CRC
field

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5–4 Data-link Layer Message Frames

BCC and CRC Fields

At the end of each polling frame and each message frame, there is
a one-byte BCC (block check character) field, or a two byte CRC
(cyclic redundancy check) field. You select BCC or CRC through
switch settings or software configuration. Either field allows you to
verify the accuracy of each message frame transmission:

• The BCC algorithm provides a medium level of data security:

– it cannot detect transposition of bytes during transmission

of a frame

– it cannot detect the insertion or deletion of the value zero

within a frame

• The CRC field provides a higher level of data security than BCC

but is more difficult to implement

BCC Field

We’ve included both half- and full-duplex BCC examples:

Half-duplex protocol example

If the master node wants to send the hexadecimal data symbols 08, 09, 06, 00, 10, 04, and
03 to slave node 20

10 01 20 10 02 08 09 06 00 10 10 04 03 10 03 B2
STN DLE STX APP DATA (DLE DLE) DLE ETX BCC

(40 octal), the master message symbols are:

16

The sum of the STN and application layer data bytes in this message frame is 4E
The BCC is the 2's complement of this sum, or B216. This is shown in the following binary
calculation:

0100 1110 = sum (4E
1011 0001 = 1's complement
+1

1011 0010 2's complement (B2

To transmit the STN or data value 10 hex, you must use the data symbol DLE DLE.
You must also use the data symbol DLE DLE if your STN value is 10. Only one of these
DLE bytes, however, is included in the BCC sum.

For example, to transmit the data values 08, 09, 06, 00, 10, 04, and 03 (hex), a slave node
uses the following message symbols:

10 02 08 09 06 00 10 10 04 03 10 03 D2
DLE STX APP DATA (DLE DLE) DLE EXT BCC

In this case, the sum of the data bytes is 2E hex because only one DLE byte is included in
the BCC. The BCC (2's complement) of 2E

)

16

= BCC)

16

is D216.

16

.

16

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Full-duplex protocol example

If a message frame contained the data 08. 09, 06, 00, 02,04, and 03 (decimal),
the message symbols are:

10 02 08 09 06 00 02 04 03 10 03 E0
DLE STX APP DATA DLE ETX BCC

The sum of the application data bytes in this message frame is 32 decimal or 20 hex.
The BCC is the 2's complement of this sum, or E0 hex. This is shown in the following
binary calculation:

0010 0000 20
1101 1111 1's compliment
+1

1110 0000

To quickly determine a BCC value, add up the hex values of the application layer bytes.
If the total is greater than 100 hex, drop the most significant digit. Then, subtract the result
from 100 hex. This gives you the BCC. For example, if the sum of the application layer
bytes is 20 hex, then:

100

16

-20

16

____
E0

16

Important: To transmit the value 10 hex, you must use the data symbol DLE DLE.

16

2's compliment (E0 hex)

However, only one of these DLE data bytes is included in the BCC sum.
For example, to transmit the values 08, 09, 06, 00, 10, 04, and 03 hex, use
the following message symbols:

5–5Data-link Layer Message Frames

10 02 08 09 06 00 10 10 04 03 10 03 D2
DLE STX APP DATA (DLE DLE) DLE EXT BCC

In this case, the sum of the application layer data bytes is 2E hex because only one DLE
byte is included in the BCC. So the BCC is D2

. This is sometimes referred to as

16

doublestuffing" DLEs.

Important: If your BBC check sum is 10 hex, send it as “10” and

not “10 10.” That is, a BCC is not treated like data.

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5–6 Data-link Layer Message Frames

CRC Field

For these protocols

fullduplex using the value of the linklayer data bytes and the ETX byte.

halfduplex

➀

The polynomial for a CRC value is:

➁

Do not add in the associated DLE for STX and ETX values.

You calculate the CRC value

•for master messages using the value of the linklayer data

bytes and the STN, STX and ETX bytes

•for slave messages using the value of the linklayer data bytes

and the ETX byte

X16 + X15 + X2 + X0.

➀

➁

Important: To transmit the data value of 1016, you must use the

data symbol DLE DLE. However, only one of these
DLE bytes is included in the CRC value.
Embedded responses are not included in the CRC value.

The following explains the transmission of the CRC value:

1. At the start of a message frame, the transmitter clears a 16-bit

register used for the CRC value.

2. As a byte is transmitted, it is exclusive-ORed (least-significant bit

to the right) with the right eight bits of the CRC register.

3. The result is placed in the right eight bits of the CRC register.

4. The CRC register is then shifted right eight times by inserting 0s

on the left. Each time a 1 is shifted out on the right, the CRC
register is exclusive-ORed with this 16-bit constant:

1010

0000 0000 0001

5. As each additional byte is transmitted, it is included in the value

in the register the same way.

6. After the ETX value is transmitted, the value in the CRC register

is transmitted (right bit first). The receiver also calculates the
CRC value and compares it to the received CRC value to verify
the accuracy of the data received.

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5–7Data-link Layer Message Frames

The full-duplex and half-duplex slave and master protocol examples
below provide you with procedures for determining the CRC-16
value.

Full-duplex and half-duplex slave protocol

data_byte = all linklayer data, ETX
CLEAR CRC_REGISTER
FOR each data_byte

GET data_byte
XOR (data_byte, right eight bits of CRC_REGISTER)
PLACE RESULT in right eight bits of CRC_REGISTER)

DO 8 times (on CRC register_

Shift bit right, shift in 0 at left
IF bit shifted = 1

XOR (CONSTANT, CRC_REGISTER)
PLACE RESULT in CRC_REGISTER

END IF

END DO
END FOR
TRANSMIT CRC_REGISTER as 2byte CRC field (low byte, high byte)

Half-duplex master protocol

data_byte = STN, STX, all linklayer data, ETX
CLEAR CRC_REGISTER
For each data_byte

GET data_byte

XOR (data_byte, right 8 bits of CRC_REGISTER)

PLACE RESULT in right 8 bits of CRC_REGISTER

DO 8 times

Shift bit right, shift in 0 at left
IF bit shifted = 1

XOR (CONSTANT, CRC_REGISTER)
PLACE RESULT in CRC_REGISTER

END IF

END DO
END FOR
TRANSMIT CRC_REGISTER as 2 byte CRC field

Below is an actual frame that you can use to validate your CRC
routine:

Use this frame to validate the CRC

53 B911 004110 02 07 00 00 00 00 00 00 00 00 00 00 00 00 10 03 6B 4C

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Chapter 6

Application Layer Message
Packets

Read this chapter to help learn about the application layer for your
asynchronous driver and the fields that your computer uses in the
application layer of a message packet. It contains these sections:

Section Page

How Your Application Program Sends and Receives Messages 6-2

Message Packet Format 6-3

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6–2 Application Layer Message Packets

application

How Your Application Program Sends and Receives Messages

There are two types of application programs:

• command initiators

• command executors

This application program Sends

command messages - specify which command function

to execute at a particular remote node
Each command message requires one reply message.
The command initiator must check for error codes and,

command initiator

command executor

Internally, Allen-Bradley asynchronous interface modules use a
routing subroutine and a message queue. When the module receives
a message over its asynchronous link, it puts the message in its
queue. The routing subroutine then takes the message from the
queue and transmits it over the DH, DH+, or DH485 network.
The module also queues messages received from the network.
The routing subroutine takes these messages and retransmits them
over the asynchronous link.

depending on the type of error, retransmit the message or
notify the user.
The command initiator should also use a timer to be aware
of lost reply messages (due to noise or other factors).
If the time limit expires before the initiator receives the
reply, the initiator can retransmit or notify the user.

reply messages - responsible for interpreting and
executing the command message.
The executor must issue a reply message for each
command it receives. If the executor cannot execute a
command, it must send the appropriate error code.

If this layer Cannot deliver a It should

generate a reply message with the

application

datalink

command message

reply message

message over the
asynchronous link

appropriate error code and send the reply to
the initiator.

destroy the reply without notification to the
command executor.

return an error message to the command
initiator.

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6–3Application Layer Message Packets

Message Packet Format

Most devices send and receive messages using this message
packet format:

Command

Reply

The bytes are shown from left to right in the order they are transmitted across the link.

Field Contents See

DST destination node for the message

SRC source node of the message

FNC function code

CMD command code

ADDR address of memory location (2 bytes) page 6-8

STS status code

EXT STS extended status code

SIZE number of bytes to be transferred page 6-8

TNS transaction number (2 bytes) page 6-7

DATA

DST CMD STS

SRC

SRC CMD STS

read

write

DST TNS

SRC CMD STSDST TNS

data values being transferred by the message
The number of data bytes in a message depends on
the command or function being executed.

TNS

Commandspecific

packet

data

ADDR

FNC

Commandspecific
data packet

SIZE DATA

page 6-4

page 6-5

page 6-6

Chapter 7

The combination of SRC, CMD, and TNS bytes uniquely identifies
every message packet. One of these fields in the current message
must be different than the corresponding field in the last message
received by a command executor. If all fields are the same, the
message is ignored and is considered to be a duplicate. If the
receiving module has the “ignore duplicate messages” option
enabled, the message will be ignored.

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6–4 Application Layer Message Packets

•0

376 (octal) for DH

DST and SRC

Form the DST and SRC bytes of a reply message by interchanging
the DST and SRC bytes of the corresponding command message:

Command

Reply

DST SRC

SRC DST

Byte Contents Value supplied by Value range

DST
(destination)

SRC
(source)

receiving message application layer

sending message data link layer

•0 to 376 (octal) for DF1

•0 to 376 (octal) for DH

to

•0 to 77 (octal) for DH+

•0 to 31 (decimal ) for DH485

When sending messages from asynchronous devices, special
consideration must be given to the SRC byte:

When sending a message from an
asynchronous device connected

to the network

➀

directly to a 1771KG

➀

If

you connect to channel 0 of a PLC5/1
send a PLC2
you put into the SRC byte is very important. This determines the compatibility file. This means
that the value of the SRC byte specifies the data table file number that is written to the PLC5
processor
compatibility file is always 9.

unprotected write, protected write, protected bit write,

. The source byte will not be overwritten by channel 0. For SLC 500 processors, the

Set the SRC byte

= 0 (the module will set the byte to its own
node number)

 10 (octal)

1, 5/20, 5/30, 5/40, 5/60 or 5/80 processor and you

or

unprotected bit write,

what

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CMD and FNC

see table that begins on

These bytes work together to define the activity that is to be
performed by the command message at the destination node.
Values for these bytes are supplied by the application layer.
The message format depends on the CMD and FNC values.

CMD byte

Bit: 7 6 5 4 3 2 1 0

Command

0

or Reply

Priority

0

Command

6–5Application Layer Message Packets

always = 0 always = 0

command message = 0
reply message = 1

➀

High

priority only applies to DH links. It does not apply to DH+, DH485, or DHII links.

This byte Defines the And has these values

CMD
(command)

FNC
(function)

Example

PLC2 command  e

send =
reply =

command type

specific function under that command type

code

nter download mode

00000111

01000111 (

(07 hex)

47 hex)
highpriority send (DH only) =
highpriority

reply (DH only) =

normal priority = 0
high priority= 1

0010011

1

01100111 (67 hex)

27

hex

command code

➀

see table that begins on
page 7-2

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6–6 Application Layer Message Packets

STS and EXT STS

These bytes work together to indicate the status of the message
transmission.

This byte In this message Has this value

STS
(status)

EXT STS
(extended status)

➀

EXT STS is part of the message only if STS = F0.

command The application program sets = 0.

reply

= 0 when the command has executed with no
error.

= one of the status codes listed in Chapter 8,

➀

reply

Message Packet Status Codes (STS, EXT
STS)." This byte will also  0 if an error
occurs.

Four high bits
of STS byte all
= 1 (F0 hex)?

No

no EXT STS byte

Application layer uses these bits (and in some cases the EXT STS byte),
to report remote errors  errors that occur when the command executor
at the destination node tries to execute the command message).

Yes

EXT STS byte

"

STS byte

STS and EXT STS error codes

For more information on STS and EXT STS error codes,
see Chapter 8, “Message Packet Status Codes (STS, EXT STS).”

32107654

Link layer uses these bits to report local errors  errors that occur
when the link layer attempts to transmit a message across the link.

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6–7Application Layer Message Packets

TNS

The TNS (transaction) bytes contain a unique 16-bit transaction
identifier. Generate this number by maintaining a 16-bit counter.
Increment the counter each time your command initiator (application
program) creates a new message, and store the counter value in the
two TNS bytes of the new message. In a multi-tasking environment,
you must use only one TNS counter, and the procedure to read and
increment the TNS must be indivisible.

command

reply

For command messages
transmitted by

a PLC the interface module assigns the TNS values.

computer node

TNS

TNS

Command executor copies the TNS field of the command message into
the TNS field of the corresponding reply message.

Command
command messages. The low byte (least significant bits) of the TNS value
is transmitted before the high byte (most significant bits).

initiator checks TNS value of reply and matches it to one of its

Values are assigned by

your application level software. The software must
assign a unique 16bit transaction number.

Important: Do not change the TNS value in a reply message.

If you change this value, the command initiator cannot
match its command to the corresponding reply message.

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6–8 Application Layer Message Packets

ADDR

The ADDR (address) bytes contain the byte address of a memory
location in the command executor where the command is to begin
executing, except in SLC 500 processors, where the ADDR byte is
interpreted as the word address.

In SLC 5/02, SLC 5/03, and SLC 5/04 processors, the CIF
Addressing Mode bit, S:2/8, can be set to a one to change the
interpretation of the ADDR byte to the byte address, so that it is
compatible with other PLC processors. For example, if the
command is to read data from the command executor, ADDR
specifies the address of the first byte of data to be read.

the low (least significant) byte of the address contains the high byte of the address

contains

ADDR

"

Sending commands to PLC-3, PLC-5, and SLC 500 processors

In some instances, when sending commands from the basic
command set to a PLC-3, PLC-5, or PLC-5/250 processor, or to an
SLC 500 processor, you must create special files to accept the data.

Important: The ADDR field specifies a byte address, not a word

address as in PLC data tables. Chapter 13, “PLC
Addressing,” explains how to convert PLC word
addresses to byte addresses. Also, if you use the
“native” read and write commands in PLC-3, PLC-5, or
SLC 500 processors, the address is not a byte address; it
is a logical binary, logical ASCII, or SLC address with
multiple address fields.

SIZE

The SIZE byte specifies the number of data bytes to be transferred
by a message. This field appears in read commands, where it
specifies the number of data bytes that the responding node must
return in its reply message.

Publication

The SIZE varies with the type of command. For PLC-5 and
PLC-5/250 typed read and typed write commands, the SIZE field
specifies the number of elements, not bytes. In PLC-5 typed read
and typed write commands, the SIZE field is two bytes long
—transmit low byte first and high byte second.

17706.5.16 - October 1996

Chapter 7

Communication Commands

This chapter contains the format you should use when sending
communication commands to Allen-Bradley processors.
Use this key to help learn the conventions that depict the
communication commands listed in this chapter:

• PLC3

processors that can
use the command

command

command
format

command name

This text describes how the command is used.

command code function code

C

reply
format

R

Unless otherwise stated, values are shown in hexadecimal.

"

CMD

Message packets

The message packets for these commands include STS and possibly
EXT STS fields that contain status and error code information.
For more information on these bytes, see Chapter 8, “Message
Packet Status Codes (STS, EXT STS).”

Protecting data files from write access

Using a PLC-5/11, -5/20, 5/30, -5/40, -5/60, or -5/80 processor,
you can also specify privileges to protect data files from write
access on a DH+ link. Using an SLC 5/02, 5/03, or 5/04 processor,
you can specify static file protection to protect data files from write
access from any of the communication channels.

FNCCMD

command description

data varies up to a maximum number of bytes

each block represents one byte

Important: In some cases, switch settings on an interface module

can disable a command at a PLC/SLC node.
For additional information on your module’s switch
settings, refer to that module’s user documentation.
(For a list of related publications and products, refer to
the preface of this manual.)

In addition to the commands listed in this chapter, we’ve also
included examples:

Section Page

PLC5 Type/Data Parameter Examples 7-36

SLC 500 Information 7-38

Reading and Writing SLC 500 Data (using SLC terminology) 7-38

Reading and Writing SLC 500 Data (using PLC2 terminology)

Publication

7-38

17706.5.16 - October 1996

7–2 Communication Commands

Use this table to locate commands you want to use. For additional
information on the commands, refer to the specified pages.

ATTENTION: Using command codes not listed will
produce unpredictable results.

!

Command CMD FNC Processors Page

Micro
Logix
1000

apply

port configuration

bit write 0F 02

change mode

close file 0F 82

diagnostic status 06 03

disable forces 0F 41

disable outputs

download all request

download completed

download request

echo 06 00

enable outputs

enable PLC scanning

enter download mode

enter upload mode

exit download/upload mode

file read 0F 04

file write 0F 03

get edit resource 0F 11

initialize memory 0F 57

modify PLC2 compatibility
file

open file

physical read

physical write 0F 08

protected bit write

protected typed file read

À

This

command cannot be executed by channel 0 of a PLC5/1

Á

The following processors can initiate these commands but cannot respond to them:

Processor Series/Revision

Series A / revision M
Series A / revision J
Series A / revision H
Series B / revision J
Series C / revision G

Â

This command has no FNC byte.

Ã

SLC 500 refers to any SLC 500, SLC 5/01, SLC 5/02, SLC 5/03, or SLC 5/04 processor

➄

Receive only

. Processors with this note cannot send the command; they receive the command from a computer

0F 8F

0F 3A

0F 80

07 00

0F 50

0F 52

0F 05

07 01

07 03

07 04

07 06

07 05

0F 5E

0F 81

04

Â

09

0F

02

Â

0F A7

Processors:

PLC5/40, 5/40L, 5/60, 5/60L
PLC5/30
PLC5/1

1, 5/20
PLC5/40, 5/40L, 5/60, 5/60L
PLC5/1

1, 5/20, 5/20E, 5/30, 5/40, 5/40L, 5/V40, 5V40L, 5/60, 5/60L, 5/80, 5/80E, 5/V80

SLC

SLC

SLC

500

5/03

5/04

1774

PLC2 PLC3 PLC5

PLC

PLC5
/250

4 4 4

➄

4

4 4

4 4
4 4 4 4
4 4 4 4 4 4 4 4 4
4 4 4 4 4

➄

4

4

4 4

4 4 4 4 4 4

4

4 4 4 4 4 4

4

4 4
4
4

4
4
4

4 4
4 4

4 4 4 4 4

4 4 4 4 4

➄

4

4

4 4 4 4

4 4

4
4

4 4 4 4 4

4 4 4 4

1, 5/20, 5/30, 5/40, 5/60, or 5/80 processor

.

.

.

4

PLC5/
VME

7-4

7-4

7-5

7-5

7-5

➄
➄

➄

4

➄

4

➄

➄

4

➄

7-6

7-6

7-6

7-7

7-7

7-8

7-8

7-9

7-9

7-9

7-10

7-10

7-10

7-11

7-11

7-12

7-12

7-13

7-13

7-13

7-14

7-15

7-16

Publication

17706.5.16 - October 1996

Command PageProcessorsFNCCMD

Micro
Logix
1000

protected typed file write

protected typed logical read
with three address fields
protected typed logical write
with three address fields

protected write

read bytes physical 0F 17

read diagnostic counters 06 01

reset diagnostic counters 06 07

read link parameters 06 09

readmodifywrite 0F 26

readmodifywrite N

read section size 0F 29

restart request 0F 0A

return edit resource 0F 12

set CPU mode

set data table size 06 08

set ENQs 06 06

set link parameters 06 0A

set NAKs 06 05

set timeout

set variables 06 02

shutdown 0F 07

typed read

typed write

unprotected bit write

unprotected read

unprotected write

upload all request (upload)

upload completed

upload 0F 06

word range read

word range write

write bytes physical 0F 18

À

This

command cannot be executed by channel 0 of a PLC5/1

Á

The following processors can initiate these commands but cannot respond to them:

Processor Series/Revision

Series A / revision M
Series A / revision J
Series A / revision H
Series B / revision J
Series C / revision G

Â

This command has no FNC byte.

Ã

SLC 500 refers to any SLC 500, SLC 5/01, SLC 5/02, SLC 5/03, or SLC 5/04 processor

➄

Receive only

. Processors with this note cannot send the command; they receive the command from a computer

0F AF

0F A2

0F AA

00

Â

0F 79

0F 3A

06 04

0F 68

0F 67

05

Â

01

Â

08

Â

0F 53

0F 55

0F 01

0F 00

Processors:

PLC5/40, 5/40L, 5/60, 5/60L
PLC5/30
PLC5/1

1, 5/20
PLC5/40, 5/40L, 5/60, 5/60L
PLC5/1

1, 5/20, 5/20E, 5/30, 5/40, 5/40L, 5/V40, 5V40L, 5/60, 5/60L, 5/80, 5/80E, 5/V80

SLC
500

4 4 4 4

4 4 4 4 4

4 4 4 4 4

4 4 4 4 4 4 4 4 4
4 4 4 4 4 4 4 4 4
4 4 4 4

4 4 4

4 4 4 4

4 4 4 4 4 4 4 4 4
4 4 4 4 4 4 4 4 4

1, 5/20, 5/30, 5/40, 5/60, or 5/80 processor

SLC

SLC

1774

Ã

5/03

5/04

PLC2 PLC3 PLC5

PLC

Á

4 4 4 4

4 4

4 4

4 4 4
4

4
4 4 4

4 4 4
4 4 4
4 4 4

➀

➀
➀
➀

4
4 4 4 4 4
4 4 4 4 4

4 4 4 4 4

4 4

4 4
4
4 4 4
4 4 4

4 4

.

.

.

PLC5
/250

4

4

4
4
4

7–3Communication Commands

PLC5/
VME

7-16

7-17

7-18

7-19

➄
➄
➄

➄
➄
➄

➄

➄

➄
➄
➄

➄
➄

➄

4

4

4

4
4

4

7-19

7-19

7-22

7-20

7-20

7-21

7-22

7-23

7-24

7-26

7-24

7-25

7-25

7-25

7-27

7-27

7-28

7-28

7-30

7-30

7-31

7-32

7-33

7-34

7-34

7-34

7-35

7-35

Publication

17706.5.16 - October 1996

7–4 Communication Commands

• PLC5

• PLC5/VME

•

SLC 5/03

•

SLC 5/04

apply port configuration

Changes the configuration of some or all ports. If there are no
parameters, changes all ports. This command reconfigures the ports
based on information in the processor’s physical memory. It is
normally used as part of a physical download operation where the
processor memory and configuration are to be fully restored.
A programming device must have the edit resource to use this
command.

"

DST SRC

C

LNH

R

HI

A
B - port numbers in this list are two bytes each, low byte first.

Data - returned only if there is an EXT STS error 12H. It contains the file and element that
relate to the error

LNH - length of the optional portion of the reply packet in bytes.

PSN PSN A B

LNH

DST

LO

- number of ports to change is a onebyte field00 means all ports."

CMD

0F

PSN SRC PSN Data

.

STS

TNS

CMD

4FH

STS

FNC

8F

TNS

EXT
STS

First four words of apply port configuration
The first four words are currently unused and unexamined.

To assure compatibility with any future use of these bytes, they
should be initialized to 0. DST, PSN, and SRC are included for
reference only.

bit write (write bit)

Publication

• PLC3

•

PLC5
(receive only)

• PLC5/250

17706.5.16 - October 1996

Modifies the bits at the address specified by either a word symbol, a
file symbol plus a word offset, or a logical address. This address
must point to a word within a file. The function code is 2. Unlike
unprotected writes and protected bit writes, this command can
change the bits in a single word only.

PLC3 Logical Address

CMD

C

R

The

STS

0F

CMD

STS

4F

EXT STS field may be attached to the reply packet only when there is an error

TNSDST SRC

TNSSRC DST

FNC

02

EXT
STS

(2  51 bytes.)

Set

Mask

Reset

.

Mask

change mode

MicroLogix 1000

Changes the mode of the MicroLogix processor.

7–5Communication Commands

•

MicroLogix 1000

•

SLC 500

•

SLC 5/03

•

SLC 5/04

C

R

DST SRC

SRC DST

CMD

0F

CMD

4F

Mode -

01 =

change to Program mode (REM program)

02 =

change to Run mode

EXT STS field may be attached to the reply packet only when there is an error

The

STS

STS

TNS

TNS

FNC

3A

EXT
STS

Mode

xxh

.

SLC 500

Changes the mode of the SLC processor. For an SLC 5/03 or
SLC 5/04 processor, change mode only works when the keyswitch is
in the REM position.

C

R

DST SRC

SRC DST

Mode -

The

CMD

STS

0F

CMD

4F

01 =
06 =
07 = change to TEST
08 = change to TEST
09 = change to TEST

EXT STS field may be attached to the reply packet only when there is an error

TNS

TNS

STS

change to PROGRAM mode (REM program)
change to RUN mode (REM Run)

SLC 500 and SLC 5/01 processors do not support 09 mode

Mode

FNC

xxh

80

EXT
STS

Cont. Scan Mode (REM T
Single Scan Mode (REM T
Debug Single Step (REM Test).

est)

est)

.

•

SLC 500

•

SLC 5/03

•

SLC 5/04

close file

Closes a file in an SLC 500 processor. When closing program file 0
(in an SLC 500, SLC 5/01, or SLC 5/02 processor) after it has been
opened for write, the SLC processor calculates the LRC for the
directory, data and internal files.

C

R

SRC DST

The

CMD

STS

0F

CMD

STS

4F

EXT STS field may be attached to the reply packet if there is an error

TNSDST SRC

EXT
STS

FNC

82

Ta g

Publication

.

17706.5.16 - October 1996

7–6 Communication Commands

• 1774PLC

• MicroLogix

• PLC2

• PLC3

• PLC5

• PLC5/250

(receive only)

•

SLC 500

•

SLC 5/03

•

SLC 5/04

1000

diagnostic status

Reads a block of status information from an interface module.
The reply contains the status information in its DATA field.
The status information varies with the type of interface module.
(For additional information, see Chapter 10, “Diagnostic Status
Information.”)

C

R

DST SRC

SRC DST

CMD

06

CMD

46

STS

STS

FNC

TNS

TNS Data

03

(max. 244 bytes)

disable forces

•

MicroLogix 1000

• PLC5

• PLC5/250

(receive only)

•

SLC 500

•

SLC 5/03

•

SLC 5/04

• 1774PLC

Disables the forcing function for I/O. All forcing data is ignored,
but remains intact.

C

R

DST SRC

SRC DST

CMD

0F

CMD

4F

STS

STS

TNS

TNS

FNC

41

EXT
STS

disable outputs

Turns off all of the 1774-PLC processor’s outputs. Use this
command to disable the outputs before sending a physical write.

C

R

DST SRC

SRC DST

CMD

07

CMD

47

STS

STS

TNS

TNS

FNC

00

Publication

17706.5.16 - October 1996

• PLC5

• PLC5/250

(receive only)

• PLC5/VME

7–7Communication Commands

download all request (download)

Places a PLC-5 processor in Download mode before downloading a
complete system. A “no privilege” error is returned if the requestor
does not have privilege to place the processor in Download mode.
This error occurs when:

• the processor is in Run or Remote Run mode (must be in Program

or Remote Program mode)

• the processor is being edited

• some other node is already downloading to the processor

• PLC5

• PLC5/250

(receive only)

• PLC5/VME

•

SLC 500

•

SLC 5/03

•

SLC 5/04

C

R

DST SRC

SRC DST

The

CMD

STS

0F

CMD

STS

4F

EXT STS field may be attached to the reply packet only when there is an error

TNS

TNS

FNC

50

EXT
STS

.

download completed

Use after downloading a complete system to place the processor
back in the mode that it was in. (For PLC-5 processors, it returns to
the mode it was in prior to executing download all request.)

C

R

DST SRC

SRC DST

The

CMD

STS

0F

CMD

STS

4F

EXT STS field may be attached to the reply packet only when there is an error

TNS

TNS

FNC

52

EXT
STS

.

Publication

17706.5.16 - October 1996

7–8 Communication Commands

• PLC3

download request (download privilege)

Used by a computer to inform an interface module that it wants to
perform a download. If the module grants the download privilege,
the computer may begin issuing physical reads or physical writes.
If another node already has the download privilege, the second node
is denied the privilege.

Before performing an upload/download, issue diagnostic status to
get the last word of memory to read or write. Bytes 11-14 in the
diagnostic status reply return E60.0.0—this is the start of unused
memory. Start your read or write at 00 00 00 00.

• 1774PLC

• MicroLogix

• PLC2

• PLC3

• PLC5

• PLC5/250

(receive only)

•

SLC 500

•

SLC 5/03

•

SLC 5/04

1000

C

R

DST SRC

SRC DST

The

CMD

0F

CMD

4F

EXT STS field may be attached to the reply packet only when there is an error

STS

STS

TNS

TNS

FNC

05

EXT
STS

.

echo

Checks the integrity of transmissions over the communication link.
The command message transmits up to 243 bytes of data to a node
interface module. The receiving module should reply to this
command by transmitting the same data back to the originating node.

C

R

DST SRC

SRC DST

CMD

06

CMD

46

STS

STS

TNS

TNS

For SLC 500, SLC 5/01, and SLC 5/02 processors, maximum data
size is 95 bytes; for SLC 5/03 and SLC 5/04 processors, maximum
data size is 236 bytes.

FNC

00

Data (max. 243 bytes)

(max. 243 bytes)

Data

Publication

17706.5.16 - October 1996

enable outputs

7–9Communication Commands

• 1774PLC

• 1774PLC

Returns control of the outputs to the 1774-PLC ladder diagram
program. Use this command to cancel the effect of disable outputs.

C

R

DST SRC

SRC DST

CMD

07

CMD

47

STS

STS

TNS

TNS

FNC

01

enable PLC scanning

Restarts the 1774-PLC processor’s program scanner after a physical
write has been performed.

C

R

DST SRC

SRC DST

CMD

07

CMD

47

STS

STS

TNS

TNS

FNC

03

• PLC2

enter download mode

Puts the PLC-2 processor in the download mode. Use this command
on a PLC-2 node before sending a physical write to the node.

C

R

DST SRC

SRC DST

CMD

07

CMD

47

STS

STS

TNS

TNS

Important: For early revisions of the 1771-KA2 and the industrial

terminal, when you send an enter download/upload
mode, the industrial terminal port is disabled until you
send an exit download/upload mode. When the
industrial terminal port is disabled, the industrial
terminal enters the mode select state. To leave this
state, you must manually select a mode at the industrial
terminal.

If you are using Use

•1771KA/A revision F

•1771KG/A

•1771KA2/B

•1771KG/B or later

FNC

04

enter download mode before sending physical read
commands.

enter upload mode before sending physical read
commands.

Publication

17706.5.16 - October 1996

7–10 Communication Commands

enter upload mode

Puts the PLC-2 processor in Upload mode. Use this command on a
PLC-2 node before sending a physical read to the node.

• PLC2

• PLC2

C

R

DST SRC

SRC DST

CMD

07

CMD

47

STS

STS

TNS

TNS

FNC

06

Important: When you send an enter upload mode, the industrial

terminal port is disabled until you send an exit

download/upload mode.

exit download/upload mode

Takes the PLC-2 processor out of the Upload or Download mode.
Use this command to restart the PLC-2 processor after performing an
upload or download operation.

Important: Do not send this command after a download/upload

command; you must recycle power to the 1771-KA,

-KA2, -KG, or 1785-KA3 module to enable industrial
terminal communication.

C

DST SRC

CMD

07

STS

TNS

FNC

05

• PLC3

• PLC5/250

R

SRC DST

CMD

47

STS

TNS

You must remove the temporary End statement from the beginning
of the program and re-insert the first byte of the program.

file read (read file)

Reads data, starting at a file symbol or a block address. This starting
address must point to a file of words.

FNC

CMD

C

R

The DATA field may be replaced by an EXT STS field if there is an error

0F

CMD

4F

STS

STS

TNSDST SRC

TNSSRC DST

Packet

Offset

04

Data  max. 244 bytes

or 122 words)

Total

Trans

Logical

(2  51 bytes.)

.

Address

Size

Publication

17706.5.16 - October 1996

7–11Communication Commands

file write (write file)

Writes data, starting at a file symbol or block address. This starting
address must point to a file of words.

• PLC3

• PLC5/250

• PLC5

• PLC5/250

(receive

only)

• PLC5/VME

•

SLC 500

•

SLC 5/03

•

SLC 5/04

Packet

C

CMD

STS

0F

(up to [239 bytes - the PLC3 logical address length]; must be an even number)

FNC

TNSDST SRC

Offset

03

This reply is the same as the reply packet for all unprotected,
protected, and privileged bit writes.

R

CMD

STS

4F

The

EXT STS field may be attached to the reply packet if an error occurs.

TNSSRC DST

EXT
STS

get edit resource

Secures the edit resource (sole access) for the programming device.
Once a programming device has obtained the edit resource, another
node cannot write to or modify the device.

DST SRC

C

R

PSN PSN

LNH

LNH

HI

DST

LO

The

EXT STS field may be attached to the reply packet only when there is an error

LNH - length of the optional portion of the reply packet in bytes.

CMD

0F

PSN SRC PSN

STS

CMD

4F

TNS

STS

Total

Trans

FNC

11

TNS

Logical

Address

(2  51 bytes.)

EXT
STS

Data

.

"

First four words of get edit resource
The first four words are currently unused and unexamined.

To assure compatibility with any future use of these bytes, they
should be initialized to 0. DST, PSN, and SRC are included for
reference only.

For this processor This access is cleared by

SLC 500, SLC 5/01, SLC 5/02 any node sending a return edit resource

the programming device or via a timed mechanism

SLC 5/03, SLC 5/04

internal to the processor sending a return edit

resource

Publication

17706.5.16 - October 1996

7–12 Communication Commands

initialize memory

Resets the processor’s memory to the default directory (the directory
the processor is shipped with). Using this command does not reset
the communication configuration.

•

MicroLogix 1000

• PLC5

• PLC5/250

(receive only)

•

SLC 500

•

SLC 5/03

•

SLC 5/04

• PLC5

C

R

DST SRC

SRC DST

CMD

0F

CMD

4F

EXT STS field may be attached to the reply packet if an error occurs.

The

STS

STS

TNS

TNS

FNC

57

EXT
STS

modify PLC2 compatibility file

Changes the compatibility mode file so that communication from a
PLC-2 processor (or a node emulating a PLC-2 processor) at the
given node address uses the file specified. This change in the default
file for PLC-2 compatibility mode remains in effect until this
command is issued again to change it or until memory is cleared.
Cycling the power to the PLC-5 processor does not reset the default.

The link ID and node address are one byte each. The file number is
two bytes.

C

DST SRC

CMD

0F

STS

TNS

FNC

5E

Link
ID

Node
Addr

File

number

Publication

17706.5.16 - October 1996

R

SRC DST

CMD

STS

4F

EXT STS field may be attached to the reply packet if there is an error

The

TNS

EXT
STS

.

open file

Opens a file in an SLC 500 processor. If the file is successfully
opened, a Tag (low byte, high byte) is returned.

7–13Communication Commands

•

SLC 500

•

SLC 5/03

•

SLC 5/04

• 1774PLC

• PLC2

• PLC3

Protection

C

R

CMD

STS

STS

TNSDST SRC

TNS

01h = read
02h = not supported
03h = read/write

0F

SRC DST

CMD

4F

Protection -

Tag is used to access the open file using a
file write. Tag is also used to close the file. The T
EXT STS field if there is an error

FNC

81

Ta g

.

File

number

protected type file read

File

type

ag field may be replaced by an

or

protected type

physical read

Uploads data from the PLC data table or program memory.

1774-PLC and PLC-2

C

R

DST SRC

SRC DST

CMD

STS

04

CMD

44

Use the SIZE field to specify the number of bytes to be read. T
PLC words, SIZE should be an even value because PLC words are two bytes.

TNS ADDR SIZE

STS

TNS

Data

(max. 244 bytes)

o specify a number of

PLC-3

For PLC-3 processors, the destination interface module accepts this
command only after the source node has successfully transmitted a
shutdown request.

DST SRC

C

R

CMD

0F

SRC DST

CMD

4F

This command must request an even number of bytes.
The

EXT STS field may replace the DATA field if there is an error

STS

STS

TNS

TNS

TNS

FNC

PLC3

09

Data

(max. 244 bytes

or 122 words)

phys. address

Size

.

Publication

17706.5.16 - October 1996