Rockwell Automation 1770-KF2 User Manual

Data Highway or Data Highway Plus Asynchronous (RS-232-C or RS-422-A) Interface Module

Cat. No. 1770-KF2)

User 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, the Allen-Bradley Company, Inc. 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 which should be taken into consideration when applying products such as those described in this publication.

Reproduction of the contents of this copyrighted manual, in whole or in part, without written permission of the 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 death, property damage or economic loss.

Attentions help you:

identify a hazard avoid the hazard recognize the consequences

Important: Identifies information that is especially important for successful application and understanding of the product.

Interchange, ControlView, Data Highway Plus and DH+ are trademarks and PLC is a registered trademark of Allen-Bradley Company, Inc.

HART is a registered trademark of Rosemount Inc. IBM is a registered trademark of International Business Machines Corporation.

Introduction 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

About This Manual 11 Module Description 13 Specifications 14 Data Highway Applications 15 PCL

Applications

Communication Concepts 21. . . . . . . . . . . . . . . . . . . . . . . . .

General 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Physical Link Layer 22 Software Layers 28

Installation 31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General 31. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Communication Mounting (Placing) 38 Interface Connections 39 Diagnostic Indicators 318

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Option Switches

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17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

31. . . . . . . . . . . . . . . . . . . . . . . . .

Asynchronous Link Protocols 41. . . . . . . . . . . . . . . . . . . . . .

General 41. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Definition of Link Protocol 41 FullDuplex Protocol 42 HalfDuplex Protocol 421

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Message Packet Formats 51. . . . . . . . . . . . . . . . . . . . . . . . . .

General 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Application Layer 51 Network Layer 51 Message Packets 53 Message Formats 57

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Data Encoding and Addressing 61. . . . . . . . . . . . . . . . . . . . .

General 61. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Encoding 61 Addressing 68

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Table of Contentsii

Error Reporting 71. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General 71. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ERROR WORD in User Programming

(1771KG, 1771KA, 1771KA2, 1774KA Modules) 72. . . . . . . . .

Error Codes for 1775KA 78 Internal Error Counters 719

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Switch Settings A1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General A1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Message Formats B1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General Asynchronous Link Error Codes (STS, EXT STS) C1.

Where to Find Asynchronous Link Error Codes C1. . . . . . . . . . . . . . .

The STS Byte C1 The EXT STS Byte C3

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Detailed Flowcharts D1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

General D1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Link Layer E1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Link Layer Operation on Data Highway E1. . . . . . . . . . . . . . . . .

Floating Master E1 Message Transmission E3 Polling E3

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Data Security E4 Link Disconnect E5

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Introduction

Chapter

General

A 1770-KF2 Series B module is a communication interface that links intelligent RS-232-C or RS-422-A (asynchronous) devices to an Allen-Bradley local area network. By setting switches on the KF2, and changing cables, you can direct communications over a Data Highway or a Peer Communication Link (PCL). With a 1770-KF2 module, a computer on a PCL can communicate with any PLC-5 node on the network. Other current Allen-Bradley products that communicate over a PCL are the 1784-T50 Industrial Terminal System and the 1785-KA Communication Adapter Module.

The KF2 is designed to operate in a control-room environment on a tabletop. It takes its power from an AC wall outlet, and it gives you a choice of full-duplex or half-duplex protocol on its asynchronous link. The module has Data Highway compatibility, and it supports all PCL facilities except internetworking.

(Internetworking would indicate that a computer on a PCL could talk to a node on another PCL, or to a station on a Data Highway link. That may be possible in the future, but it isn’t right now. A computer on a Data Highway, though, using a 1770-KF2 and a 1785-KA can communicate with PLC-5s on a PCL.)

About This Manual

This manual describes installation, operation, and communication protocols of a 1770-KF2 module; and it assumes that you are already thoroughly familiar with how to program your computer or other intelligent asynchronous device. It does not assume prior knowledge of the Allen-Bradley Data Highway or a Peer Communication Link.

Table 1.A lists related documentation that might be helpful in conjunction with this manual. For more details about the programming and operation of specific Allen-Bradley programmable controllers, refer to the appropriate user’s manual for that controller.

1-1

Chapter 1

Introduction

able 1.A

Documentation

Publication

Number

1770-6.2.1 1770-810

1771-6.5.1 1771-801

1771-6.5.15 1771-822

1771-6.5.8 1771-811

1775-6.5.1 1775-802

1773-6.5.2 1773-801

1785-6.8.1 1785-6.6.1 6226-6.5.1

Old Publication

Number

Title

Data Highway Cable Assembly and Installation Manual

Communication Adapter Module (Cat. No. 1771-KA2) User’s Manual

Communication Controller Module (Cat. Nos. 1771-KE, -KF) User’s Manual

PLC-2 Family/RS-232-C Interface Module (Cat. No. 1771-KG) User’s Manual

PLC-3 Communication Adapter Module (Cat. No. 1775-KA) User’s Manual

PLC-4 Communication Interface Module (Cat. No. 1773-KA) User

PLC-5/15 Processor Manual PLC-5/15 Assembly & Installation Manual Industrial Terminal Support Software System

Manual

’

s Guide

1784-6.5.1 1785-6.5.1

Industrial T PCL-to-Data Highway Communication Adapter

Module (1785-KA) User’s Manual

erminal (1784-T50) User’s Manual

This manual is organized as follows:

Chapter 2 — Explains basic communication concepts. Chapter 3 — Tells how to install a KF2 module. Chapters 4, 5, and 6 — Describe the communication protocol used by

a KF2 module.

Chapter 7 — Summarizes error reporting.

1-2

Chapter 1

Introduction

Module Description

Figure 1.1 shows the 1770-KF2 module’s hardware features:

Diagnostic Indicators Connectors for Data Highway and RS-232-C Devices Communication Option Switches On/Off Switch, Power Plug, Fuse, and Voltage Select Switch

Figure 1.1 1770-KF2

Communication Interface Module

ALLEN–BRADLEY

DATA HIGHWAY COMMUNICATION INTERFACE

XMTG RCVG RDY ACTV CPUPWR

A KF2 also features extensive self-diagnostics. At power-up, tests are run on internal memory, timers, and firmware integrity. Any failure causes the red front-panel CPU indicator to flash. Also, the module continuously checks the memory and firmware during operation.

1-3

Chapter 1

Introduction

Specifications

Table 1.B lists KF2 module specifications.

able 1.B

KF2

Module Specifications

Specification Requirements

Communication Rates

Functions

Location

Communication Ports

•

Data Highway: 57,600 bits per second (recommended)

•

Peer Communication Link: 57,600 bits per second (recommended)

•

Asynchronous: Switch selectable from 1 per second

•

Interface a programmable RS-232-C or RS-422-A compatible device with an Allen-Bradley Data Highway

•

Serve as a replacement for a 1771-KD Communication Controller Module.

• T

abletop (or other horizontal surface)

•

Controlled environment, e.g., of

•

Data Highway: 15-pin male EIA D-connector

•

Peer Communication Link: 15-pin male EIA D-connector

•

Data Highway Monitor: 9-pin female EIA D-connector

•

Asynchronous (RS-232-C/RS-422-A): 25-pin male EIA D-connector

10 to 9.600 bits

fice or control room

Cabling

Power Requirements

Ambient T Rating

Ambient Humidity Rating Physical

emperature

•

Data Highway: Data Highway Dropline Cable (Cat. No. 1770-CD)

•

Asynchronous RS-232-C: User-Supplied Data T

erminal Interface Cable or Modem Interface Cable

•

Asynchronous RS-422-A: User-Supplied Data T Interface Cable

•

Selectable: 115 V/60 Hz or 230 V/50 Hz

• W

atts: 3.5

• 32oF to 1

• -40oF to 185oF (-40oC to 85oC) Storage

•

10% to 80% Non-Condensing

•

Size: 10-3/8 in. x 10.0 in. x 3-3/8 in. (263.5 mm x 254 mm x 85.7 mm)

• W

13oF (0oC to 45oC) Operational

eight: 6.0 pounds (2.7 Kg)

erminal

1-4

Chapter 1

Introduction

Data Highway Applications

A KF2 module provides either a point-to-point link or a multi-drop link between an Allen-Bradley Data Highway and an intelligent asynchronous device. By “intelligent asynchronous device” we mean any device that complies with RS-232-C or RS-422-A electrical standards and that can be programmed to handle the communication protocol described in Chapters 4 through 6 of this manual. Throughout this manual, we will also use the term “computer” in a general sense to refer to this type of device. Some examples include:

An Allen-Bradley Advisor 2+TM Color Graphic System A PLC-3 Programmable Controller and Connected Communication

Adapter Module (Cat. No. 1775-KA)

A PLC-2 Family Programmable Controller and Connected PLC-2

Family/RS-232-C Interface Module (Cat. No. 1771-KG)

A PLC-4 Microtrol Programmable Controller and Connected

Communication Interface Module (Cat. No. 1773-KA)

A Variety of Minicomputers and Microcomputers

In point-to-point configuration, the KF2 module connects one intelligent asynchronous device as a single station on a Data Highway. Figure 1.2 illustrates this configuration. Point-to-point links can use either peer-topeer (full-duplex) or master-slave (half-duplex) communication.

Figure 1.2 Point-to-Point

Links

Computer

Modem

Modem Link

Modem

KF2 Module KF2 Module

Allen–Bradley Longline RS-232-C Link (7,000 Cable-Ft. Max.)

Asynchronous Link (50 Cable-Ft. Max.)

KF2 Module

Data Highway Link

1771-KG Module

PLC-2/30 Processor

Computer

11687

1-5

Chapter 1

Introduction

In a multi-drop configuration, one intelligent asynchronous device connects to several Data Highways through sets of modems and KF2 modules. Figure 1.3 illustrates this type of configuration. If the multi-drop link consists of broadband modems, you can select either peer-to-peer (full-duplex) or master-slave (half-duplex) communication. If the multi-drop link consists of baseband modems, you must use master-slave (half-duplex) communication because baseband modems support only one communication channel.

Figure 1.3 Multi-Drop

Link

Computer

1775-KA Module

PLC-3 Processor

Modem

KF2 Module

1773-KA Module

PLC-4 Microtrol Processor

Modem

Multi-Drop Modem Link

Modem

1771-KG Module

Data Highway Link

PLC-2/15 Processor

Modem

KF2 Module

Data Highway Link

1-6

KF2 Module

Computer

1771-KA Module

PLC-2 Processor

1774-KA Module

PLC Processor

11688

Chapter 1

Introduction

In either type of configuration, there are three possible ways you can connect a KF2 module:

Direct connection to an intelligent asynchronous device if the KF2

module is mounted within 50 cable-feet of an RS-232-C, or within 4,000 cable-feet of an RS-422-A device.

Direct connection to an Allen-Bradley 1775-KA, 1773-KA, or

1771-KG interface module if the KF2 module is within 50 cable-feet of the other module.

Modem connection if the KF2 module is within 50 cable-feet of an

RS-232-C compatible modem, or within 4,000 cable-feet of an RS-422-A device.

You can also use the 1770-KF2 module to replace a 1771-KD module in an existing application. By properly setting the option switches on the KF2 module, you can make this replacement without having to change any application programs that you were using with the 1771-KD module. Refer to Chapter 3 under “Replacing a 1771-KD Module with a KF2 Module” for switch settings.

PCL Applications

A 1770-KF2 Series B module provides either a point-to-point or multi-drop link between an Allen-Bradley Peer Communication Link (PCL) and an intelligent asynchronous device. You can use a PCL link when you have a small number of PLC-5/15 stations in a local cluster. Typically, a PCL link connects PLC-5/15s that need to communicate with each other frequently. If your system requires more than ten stations, consider breaking it into smaller PCL links connected by a Data Highway to optimize performance.

The KF2 Series B module provides an interface between either:

an RS-232-C or RS-422-A asynchronous link to Data Highway, or an RS-232-C or RS-422-A asynchronous link to a PCL network as

shown in Figure 1.4.

1-7

Chapter 1

Introduction

Figure 1.4 A

PCL Network Connected to a Data Highway

1770-KF2

1785-KA

PLC-3

1775-KA

PCL

Advisor 2+

Data Highway

PLC-5 PLC-5 1770-KF2

1-8

Computer

14690

Important: A 1770-KF2 module on a PCL link cannot access a station on the Data Highway through a 1785-KA module. A KF2 module on the Data Highway, however, can access a station on a PCL link through a 1785-KA.

Chapter

Communication Concepts

General

This chapter presents some of the concepts of communication with the KF2 module. It describes the physical communication links to the module and the various levels of software necessary to make those links work.

A KF2 module connects a computer or programmable controller to an Allen-Bradley local area network (LAN), either Data Highway or Peer Communication Link (PCL). In doing so, the module acts as an interface between two physical communication links:

Data Highway or PCL, Called “Network Link” RS-232-C or RS-422-A, Called “Asynchronous Link”

A Data Highway network provides peer-to-peer communication between the KF2 module and other stations on the Data Highway. It uses a half-duplex (polled) protocol and rotation of link mastership.

A Peer Communication Link provides peer-to-peer communication between the KF2 module and other stations on the PCL. The PCL uses token-passing to control access to the link.

The asynchronous link can provide either peer-to-peer communication through a full-duplex (unpolled) protocol, or master-slave communication through a half-duplex (polled) protocol.

In addition to a physical link layer, communication on either the network link or the asynchronous link involves three levels of software:

Application Layer Network Layer Data Link Layer

If you are using a computer on an asynchronous link, you must program all three layers. For A-B programmable controllers, you need program only the application layer; the Data Highway interface modules (or for the PCL, the PLC-5 itself) automatically take care of the other two layers.

The rest of this chapter presents some of the concepts behind the physical communication links and their three software layers. For more details on

2-1

Chapter 2

Communication Concepts

the application and network layers, refer to Chapters 5 and 6. For more on the data link layer of the asynchronous link, refer to Chapter 4 and Appendix D.

Physical Link Layer

The physical link layer is a set of cables and interface modules that work together to provide a channel for communication between the various points, called stations, on the physical link. A station consists of an intelligent programmable device (e.g., PC or computer) and the module or modules that interface it with the physical link.

In this way, the KF2 module allows stations on one link to communicate with stations on the other link. Since these two physical links have different communication protocols, the KF2 module serves mainly as a protocol translator.

Data Highway

The Data Highway and the PCL are both local area networks (LANS) that allow peer-to-peer communication among up to 64 stations. Figure 2.1 illustrates a Data Highway network.

The Data Highway link consists of a trunkline that can be up to 10,000 feet long and droplines that can be up to 100 feet each. Each station is at the end of a dropline.

2-2

A Data Highway link implements peer-to-peer communication through a modified token-passing scheme called the floating master. With this arrangement, each station has equal access to become the master. The stations bid for temporary mastership based on their need to send information.

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

Figure 2.1 Data

Highway Network

Chapter 2

Communication Concepts

PLC-3

Processor

1775-KA

Module

Computer

MODEM

1770-KF2 Module

MODEM Link

Advisor 2+

1770-KF2 Module

RS-232-C Link 50 Cable-Ft. Max.

Data Highway Link

1770-KF2 Module

RS-232-C Link 50 Cable-Ft. Max.

1771-KA

Module

PLC-2/15 Processor

1773-KA Module

PLC-4

Loop

1771-KG Module

PLC-2/30 Processor

Stations

A station consists of a computer or PC processor and the module or modules that interface it with the Data Highway link. Within a station that contains a KF2 module, an asynchronous link is required as an auxiliary link to the network. Figure 2.1 shows three such stations.

11299A

2-3

Chapter 2

Communication Concepts

One station consists of an Advisor 2+TM Color Graphic System connected to a KF2 module through an RS-232-C link limited to 50 cable-feet. Another station consists of a computer interfacing with a KF2 module through a modem link that is limited only by the nature of the modems themselves.

The third such station consists of a 1771-KG module interfacing a PLC-2/30 processor with a KF2 module through an RS-232-C link limited to 50 cable-feet. If you want a link longer than 50 cable-feet, you can use modems.

PC Programming

All Allen-Bradley PC processors can be connected to a Data Highway through an appropriate station interface module. All of these processors can receive and reply to command messages, and some of them can also transmit command messages. For an explanation of how to program PCs to send and receive messages, refer to the user’s manual for the appropriate station interface module.

Computer Programming

The communication protocol for the Data Highway link is transparent to a computer on the network. However, for a computer to send or receive messages through the Data Highway network, it must be programmed to communicate with its KF2 module over an asynchronous link. Chapters 4, 5, and 6 describe the protocol that you must program your computer to use on such an asynchronous link.

Peer Communication Link

A PCL has much the same topology as the Data Highway, described in the previous chapter; but it is designed for fewer, closely coupled, PCs. The PCL implements peer-to-peer communication with a token-passing scheme to rotate link mastership among the stations connected to that link. Since such a method does not require any polling, it is very time efficient. The PCL also uses timeouts to recover from any fault that disables the station that has the token.

2-4

Chapter 2

Communication Concepts

Stations

A station consists of a computer, or PC processor, and the module or modules that interface it with the PCL. Within a station that contains a KF2 module, an asynchronous link is required as an auxiliary link to the network. PCL networks currently use PLC-5 processors, which interface directly to the PCL; and no station interface module is required. You can, however, connect other PCs, as shown in Figure 2.2.

Figure 2.2 PCL

Network Connected to V

arious PC Processors

PLC-4

Loop

1773-KA

Module

KF2

Module

PLC-3

Processor

1775-KA

Module

KF2

Module

PLC-2/30 Processor

1771-KG

Module

KF2

Module

PCL

11300A

Other PCL stations can be computers that interface with the KF2 module either directly or through a modem link, or a PCL-to-Data Highway communication adapter (1785-KA), which you can use to connect a PCL to the Data Highway.

PC Programming

All Allen-Bradley PC processors can receive command messages and reply to them, and some can transmit commands. For an explanation of how to program PCs to send and receive messages, refer to the user’s manual for that particular station interface module or, in the case of a PLC-5, the processor itself.

2-5

Chapter 2

Communication Concepts

Computer Programming

The communication protocol for the PCL is transparent to a computer on the network. However, for a computer to send or receive messages through the PCL, it must be programmed to communicate with its KF2 module over an asynchronous link. Chapters 4, 5, and 6 describe the protocol that you must program your computer to use on this link.

Configuration Selection

Figure 2.1 and Figure 2.2 illustrate configurations in which PC stations can communicate with each other and with computers through network ports and asynchronous ports on the station interface modules. Each configuration is useful, depending on your application.

If you want to provide a peer-to-peer communication among many PCs and/or a computer, use a Data Highway network as shown in Figure 2.1. For communication among a small cluster of PCs and a computer, use a PCL as shown in Figure 1.4. For distances longer than the networks provide, you can use an auxiliary longline asynchronous (RS-232-C or RS-422-A) link or a modem link.

A Data Highway link has a communication rate of 57,600 bits per second and a half-duplex (peer-to-peer, polled) protocol. A KF2 asynchronous link is selectable RS-232-C/RS-422-A and has a selectable communication rate up to 9,600 bits per second. It uses a selectable protocol of half-duplex (master-slave polled) or full-duplex (peer-to-peer, unpolled).

A master-slave communication protocol can be selected for any link to a computer. A peer-to-peer communication protocol can be selected only for a point-to-point link or a broadband modem multi-drop link to a computer.

Even with only two stations, you may want a Data Highway or a Peer Communication Link. Either network provides the flexibility of easy reconfiguration or expansion if you want to be able to add more stations later, and it also provides more error checking than an asynchronous link.

2-6

Chapter 2

Communication Concepts

Configuration Considerations

Allen-Bradley manufactures a variety of communication interface modules for different applications:

Communication

PLC Communication Adapter Module PLC-2 Family Communication Adapter Module PLC-3 Communication Adapter Module PLC-4 Communication Interface Module PLC-5/Data Highway Communication Adapter Module PLC-2 Family/RS-232-C Interface Module Communication Controller Modules Communication Interface Module

Provides interface between:

A PC Processor and a Data Highway Communication Link

A PC Processor and an RS-232-C Communication Link

A RS-232-C Communication Link and a Data Highway Communication Link

Interface Module

Cat. No.

1774-KA 1 1771-KA2 1 1775-KA 1773-KA 1785-KA –– 1771-KG 2 1771-KE, -KF 1770-KF2B 3

Note

1 & 2 1 & 2

A 1785-KA module interfaces a Data Highway with a Peer Communication Link. The module resides in a 1771 I/O rack and receives its power from the rack’s backplane.

A 1771-KE module must be installed in an I/O chassis. The 1771-KD, 1771-KF, and 1770-KF2 are standalone modules. Modules 1771-KE, 1771-KF, and 1770-KF2 provide either peer-to-peer or master-slave communication between an RS-232-C link, or to a modem link, and the Data Highway.

RS-422-A/Data Highway Interface

A 1770-KF2 provides an interface between an RS-422-A communication link and a Data Highway communication link. The 1770-KF2 is functionally identical to the 1771-KF except that it is a desktop module, provides its own power supply, and supports both RS-232-C and RS-422-A communication.

RS-232-C/RS-422-A — PCL Interface

A 1770-KF2 provides an interface between an RS-232-C or RS-422-A asynchronous link and a Peer Communication Link network.

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Chapter 2

Communication Concepts

Software Layers

Each of the physical links just described requires three layers of software to enable communication to take place. The layers are defined as follows:

Application Layer — Controls and executes the actual tasks, or

commands, specified in the communication between stations. To program this layer, use the commands described in Chapter 5.

Network Management Layer — Handles queueing, sequencing,

routing, and error status reporting for communication. If your physical link contains only Allen-Bradley PCs, you do not have to program this layer. Otherwise, refer to Chapter 5 for a description of how to program this layer for an asynchronous link to a computer.

Data Link Layer — Controls the flow of communication over the

physical link by establishing, maintaining, and releasing the communication channel between stations. If your physical link contains only Allen-Bradley PCs, you do not have to program this layer. Otherwise, refer to Chapter 4 for a description of how to program this layer for an asynchronous link to a computer.

Application Layer

The application layer concerns the specific commands that you can program at a given station to cause that station to communicate over the link. This layer is the same for both asynchronous and network links.

The types of commands that a station can transmit and receive vary with the type of processor at that station. Chapter 5 describes the commands that each type of PC processor can transmit or receive. To program your computer to communicate with a PC, use the appropriate command message format shown in Chapter 5.

Message Structures

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

Protocol Bytes Data Bytes

Protocol bytes are used by the network to get the message to its destination. Data bytes are delivered to the application at the destination.

The methods by which these bytes are filled is determined by the nature of the station from which the transmission block originates. For example, if a transaction originates from a PC station, the station interface module

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Chapter 2

Communication Concepts

automatically fills the protocol bytes. If the transaction originates from a computer station, your computer software must supply the necessary protocol. In both cases, the data bytes contain information supplied by application programs.

Command/Reply Cycle

Any network transaction consists of two messages: a command and a reply.

The two parts provide extra data integrity by ensuring that a required action always returns some sort of status, whether an error code or data. As a frame of reference, the command initiator is always referred to as a local station, and a reply initiator is always referred to as a remote station. Unless noted otherwise, whether in a network link or an asynchronous link, our reference will be limited to a single local station and a single remote station.

The network layer protocol distinguishes a command from a reply. Obviously, the data area of a command and its corresponding reply depend on the type of command.

Priority

Each message on a Data Highway link is classified as either high priority or normal priority.

Each message on a PCL is classified as normal priority.

Priority levels of messages determine the order in which stations are polled and allowed to transmit messages. In the polling process, stations with high priority messages will always be given priority over stations with normal priority messages.

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

Important: Stations with high priority messages are given priority over stations 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

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Chapter 2

Communication Concepts

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.

Command Structures

There are four basis types of command on a Data Highway network or a standalone link:

Read Write Diagnostic Mode Select

Reads

There are two types of read:

Physical Unprotected

A physical read allows you to read any area of PC memory at a remote station. However, a PC processor cannot originate a physical read command; only a computer can originate a physical read.

An unprotected read can access only the data table area of PC memory. Both computers and PCs can initiate unprotected reads.

Any read can request up to 122 16-bit words of contiguous data from PC memory.

Writes

We can classify write commands both by their application and by their level of memory access.

2-10

As an application issue, writes are divided between bit writes and word writes. Bit writes allow the local station to control bits in the data table of a remote station.

Word writes allow the local station to write up to 121 contiguous words of data into the remote station’s memory, provided you abide by the restrictions on memory access discussed next.

Chapter 2

Communication Concepts

As with reads, writes also are classified by the level of access to PC memory. Non-physical writes can access only the data table at a remote PC; physical writes can access all of user memory, including PC program memory.

Non-physical writes can be further subdivided into protected and unprotected. Protected writes can access only specified areas of the remote PC’s data table memory. The accessible areas are defined by memory protection rungs in the remote PC’s ladder diagram program. Unprotected writes, on the other hand, can access any area of the remote PC’s data table.

In most cases, switch settings on the remote station’s interface module can disable the module from executing each of these types of write commands.

Diagnostics

Diagnostic commands have to originate from a device other than a PC. You can use these commands to return status information from a remote or local station or to alter some on-board parameters at a station interface module. Diagnostic commands are particularly useful during a start-up or during on-line debugging.

Mode Select

Mode select commands allow you to load a new PC program from a remote computer station. The operation of these commands varies by PC processor type. These commands can be issued only by a computer.

Network Management Layer

The network management layer is concerned with the specifics of conveying a message safely from its source to its destination. This layer is the same for both asynchronous and network links.

If your physical link contains only Allen-Bradley PCs, you do not have to program anything for this layer; the communication interface modules automatically take care of it. If your physical link contains a computer, then refer to Chapter 5 for a description of how to program this layer at the computer station.

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Chapter 2

Communication Concepts

Generally, you need not be concerned with the interaction of station interface modules on the network.

This means that your application programs at the PCs and computers along the network need not involve themselves with interstation protocol, handshaking, or control of the network link. This is all carried out automatically by the station interface modules. However, an understanding of station interaction is useful both to computer programmers and PC programmers. It allows optimum use of network commands and fault diagnostics.

Error Checking

Error codes can be generated at two places: remote station modules and local station interface modules. For codes that are returned from a local station module, two types of condition can exist:

Application programs use the wrong message format or issue illegal

commands.

The local station cannot complete a transaction due to network

problems.

A remote station can return only the codes associated with an application problem at the remote station. Typically, these involve either the PC processor being off-line (in Program mode, for example) or the command trying to access memory areas blocked by either the interface module or the user application program.

In the network layer protocol, command message status is returned in a reply status byte. A value of zero in the status byte indicates successful transmission of the corresponding command. It is up to the local application program to display and act on the value of the returned byte.

2-12

Installation

Chapter

General

Communication Option Switches

This chapter explains how to install the 1770-KF2 module. There are four parts to installation:

Setting Communication Option Switches Situating the Module for Operation Connecting the Module to the Network and Asynchronous Links Observing the Diagnostic Indicators

Please read the first three chapters of this manual carefully before attempting any of the installation steps.

The KF2 module has 8 switch assemblies (Figure 3.1) that enable you to select various communication options. The switch assemblies and their corresponding options are:

Switch

Assembly

SW-1 SW

-2, SW-3, SW SW-5 SW-6

SW-7

SW-8

-4

Communication Option

Asynchronous Link Features Station Number Network Link Communication Rate Asynchronous Link Communication Rate and Diagnostic

Commands

Selecting the Network Link

RS-232-C/RS-422-A Selection

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Chapter 3

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Figure 3.1 Communication

RS-232-C/RS-422-A Selection (SW-8)

Option Switches

Asynchronous Link Features (SW-1)

Network Link Communication Rate (SW-5)

Station Number (SW-2, SW-3, SW-4)

Asynchronous Link Communication

Rate (SW-6)

Network Link Selection (SW-7)

O N

O F F

O N

O F F

345

O N

O F F

123

O N

O F F

123

O N

O F F

O N

O F F

1234

O N

O F F

O N

O F F

Front View Side View

O N

O F F

OFF

13529

Important: The KF2 reads the status of the communication option switches only at power-up, so you must make your selection with the KF2’s power off.

Asynchronous Link Features

The following table shows you how to set the asynchronous link features using Switch Numbers 1, 2, and 5.

If You W

Protocol as:

Full Duplex Full Duplex Full Duplex Full Duplex Half Duplex Half Duplex Full Duplex Half Duplex

to Select

ant

ith Error

Check as: Parity as:

BCC None No OFF OFF N/A N/A OFF BCC Even No ON OFF OFF BCC None Yes OFF ON OFF BCC Even Yes ON ON OFF BCC None No OFF OFF ON BCC Even No ON OFF ON CRC None Yes OFF ON ON CRC None No ON ON ON

With

Embedded SW-1

Responses: 1 2 3 4 5

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Chapter 3

Installation

Switch 3 determines whether the asynchronous port of the KF2 module can detect duplicate messages transmitted to it.

If You W

Detect and Ignore Duplicate Messages Accept All Messages Regardless of Duplication

ant Y

our Module to:

Set Switch 3:

OFF

Switch 4 determines whether the module uses and recognizes the following handshaking signals: data set ready, request to send, clear to send, data carrier detect, and data terminal ready.

If You W

Use Handshaking Signals Ignore Handshaking Signals

ant the Module’s Asynchronous Port to:

Set Switch 4:

OFF

Important: If you select half-duplex, the KF2 uses handshaking signals even if Switch 4 is set OFF.

Station Number

Switch Assemblies SW-2, SW-3, and SW-4 are for setting the network station number of the KF2 module. For the Data Highway, the station number is a 3-digit octal number that identifies the KF2 module as a unique station. Valid station numbers for the KF2 module in Data Highway mode are 010 to 077 and 110 to 376 octal. For a PCL, the station number is 2 digits; set both switches in SW-2 OFF. Valid station numbers for the KF2 in PCL mode are 00 to 77 octal.

Figure 3.2 shows an example of how to set the KF2 station number to 037 octal. The switches in Assembly SW-2 set the first (left-most) digit of the station number; Switch Assembly SW-3 sets the middle digit; and Switch Assembly SW-4 sets the last (right-most) digit.

Station numbers play an important part in the polling scheme described in Chapter 2. They can also influence the order in which mastership is transferred between network stations. Therefore, we recommend that you always begin numbering stations with the lowest possible number and continue with the next available number in sequence.

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Installation

Figure 3.2 Station

Number

Switch Groups

SW-2 SW-3 SW-4

O N

O F F

First Digit Second and Third Digits

If You Want to Set This

Digit:

0 1

2 3

O N

O F F

Set Switches

No. 1 No. 2

OFF OFF OFF ON

ON OFF ON ON

O N

O F F

If You Want to Set This

Digit:

0 1

2 3 4 5

6 7

No. 1 No. 2

OFF OFF OFF OFF

OFF ON OFF ON ON ON

ON ON

OFF

Set Switches

OFF OFF

ON ON

OFF

No. 3

OFF ON

OFF ON OFF ON

OFF ON

3-4

Switch Setting Example: Station No. 037 Switch Group SW-2 SW-3 SW-4

Station No. Digits 0 3 7

Switch No. Switch Setting

12123

OFF OFF OFF ON ON ON ON ON

123

13531

Network Communication Rate

Switch Assembly SW-5 lets you select the communication rate for the KF2 module’s network link.

Important: Set both switches ON for a network communication rate of 57,600 bits per second. Be sure to set all modules on the network link for this communication rate.

Chapter 3

Installation

Figure 3.3 Switch

Settings for Network Link

SW–5

O N

O F F

Both switches ON for 57,600 bits per second

13514

Asynchronous Communication Rate and Diagnostic Commands

Switch Assembly SW-6 lets you select the communication rate and diagnostic commands for the KF2 module’s asynchronous port.

Communication Rate

Set the communication rate switches as shown:

Bits

per

Second as:

110 OFF OFF OFF 300 ON OFF OFF

600 OFF ON OFF 1,200 ON ON OFF 2,400 OFF OFF ON 4,800 ON OFF ON 9,600 OFF ON ON

Set Switch:

1 2 3

Diagnostic Commands

Switch 4 determines how the KF2 module treats diagnostic commands sent to it by a remote Data Highway station. You can connect the asynchronous port of the KF2 module directly to a 1771-KG, 1773-KA, or 1775-KA communication interface module (Figure 1.2). In such applications, you can set Switch 4 so that the KF2 module either executes any received diagnostic commands itself or passes those commands to the other attached communication module.

If You W

Execute Received Diagnostic Commands Pass Any Received Diagnostic Commands to the

Attached Asynchronous Device

ant Y

our Module to:

Set Switch 4:

OFF

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Chapter 3

Installation

Switch 4 relates only to diagnostic commands sent to the KF2 module from a remote Data Highway station. Since only computers can transmit diagnostic commands, the remote station must be a computer connected to the Data Highway by means of another KF2 module. At the computer station, the setting of Switch 4 does not affect any diagnostic commands that the computer sends to its local KF2 module. The local module always retransmits the command message over the Data Highway without executing it. Figure 3.4 illustrates these concepts.

Figure 3.4 Effect

of Switch 4 on Diagnostic Commands

Switch 4 ON

1770-KF2 Module

Computer

Diagnostic Command Path Reply Message Path

Computer

1770-KF2 Module

Data Highway Link

o Other Stations

Data Highway Link

o Other Stations

1771-KG Module PLC-2/15 Processor

Switch 4 OFF

1770-KF2 Module

1771-KG Module PLC-2/15 Processor

11691

You can have more than one computer station on a network, and one computer can transmit diagnostic commands to the others. At the receiving computer station, if Switch 4 is OFF, the local KF2 module will pass the diagnostic commands to the computer. In such cases, you will have to write computer application programs to handle those commands at the receiving station. If Switch 4 is ON at the receiving station, the local KF2 module itself will execute the incoming diagnostic commands.

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Chapter 3

Installation

Selecting the Network Link

You use Switch Assembly SW-7, a spare assembly in all Series A modules, to select whether the KF2 treats the network link as a Data Highway or as a PCL.

The following table shows the settings for Switch Assembly SW-7:

For

This Network:

Data Highway Peer Communication Link

Set Switch 1: Set Switch 2:

OFF OFF

ON OFF

Selection of RS-232-C/RS-422-A

Switch Assembly SW-8 lets you select whether the asynchronous interface uses RS-232-C or RS-422-A standard communication.

For

Communication Using Standard:

RS-232-C OFF ON RS-422-A ON OFF

Set Switch 1: Set Switch 2:

Important: This is the only option switch that affects KF2 operation after power-up. It changes the voltage applied to the network link connector pins to those required for the standard selected. Set this switch BEFORE power-up.

Replacing a 1771-KD Module with a KF2 Module

By setting the switches properly on the KF2 module, you can use it to replace an older 1771-KD module in an existing application without having to make any changes in your application programs.

In Set

Switch Ass’y

SW-1 1 OFF

SW-2 1, 2 Same Setting as 1771-KD Switches (Assembly SW-2, Switches 1 and 2) SW-3 1, 2, 3 Same Setting as 1771-KD Switches (Assembly SW-3, Switches 1, 2, and 3) SW-4 1, 2, 3 Same Setting as 1771-KD Switches (Assembly SW-4, Switches 1, 2, and 3) SW-5 1, 2 Same Setting as 1771-KD Switches (Assembly SW-5, Switches 1 and 2) SW-6 1, 2, 3 Same Setting as 1771-KD Switches (Assembly SW-6, Switches 1, 2, and 3)

SW-7 1, 2 OFF SW-8 1 OFF

Switch

No.

2 Same Setting as 1771-KD Switch (Assembly SW-1, Switch 1) 3 OFF 4 OFF 5 OFF

4 Same Setting as 1771-KD Switch (Assembly SW-1, Switch 5)

2 ON

Setting

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Chapter 3

Installation

Important: The asynchronous port of the KF2 module can communicate at a maximum rate of 9,600 bits per second. If your 1771-KD module was set to communicate at a higher rate, then you might have to make some modifications to your RS-232-C link before installing the replacement KF2 module.

Mounting (Placing)

A KF2 module is not actually mounted in the sense that other Allen-Bradley communication modules are. It is simply situated on a surface, like a desktop, near a wall plug for AC power. It is set for 115V operation when it reaches you. Connections to 115V AC and 230V AC are described below.

Place the KF2 module within 100 cable-feet of the Data Highway trunkline. If you are connecting the module directly to an RS-232-C device, you must also mount the module within 50 cable-feet of that device. If you are using a modem link to connect the KF2 module to the asynchronous device, then the module and the device may be as far apart as the modem link will allow. If you are connecting the KF2 directly to an RS-422-A compatible device, you must mount the module within 4,000 cable-feet of that device.

115V AC Operation

The “power select” switch is above the ON/OFF switch on the module’s rear panel. Set this switch to “115.” The power cord (approximately 7’4”), supplied with the module, must be plugged into the receptacle at the right of the ON/OFF switch. Plug the other end of the power cord into any standard 115V AC power outlet. Switch must be set before power-up.

3-8

230V AC Operation

Set the “power select” switch to “230.” Do NOT use the power cord supplied with the module. This cord is not approved for connection to a

230V AC outlet. To guard against electrical shock or fire, the power supply cord must be approved for 230V AC by Underwriters Laboratories or a similarly recognized agency. To mate with the receptacle on the module’s rear panel, the power cord must be terminated in a molded female connector (CEE 22 Standard V).

Chapter 3

Installation

Interface Connections

The KF2 module has 3 connectors on its rear panel (Figure 3.5). The center connector, labeled DATA HIGHWAY, connects to the Data Highway dropline cable. Plug the 15-pin connector of the dropline into the DATA HIGHWAY socket. For connection to the PCL, plug the 15-pin PCL dropline into the Data Highway socket. (For details on how to construct the dropline, refer to Publications 1770-6.2.1 or 1770-2.13.)

The left connector, labeled DATA HIGHWAY MONITOR, is for future product development. Do not make any connections to this socket.

The right connector, labeled COMPUTER ASYNCHRONOUS, connects to an intelligent RS-232-C or RS-422-A compatible device. The rest of this section explains how to make connections to this asynchronous socket.

Figure 3.5 Dimensions

of a 1770-KF2 Series B Module

10” (254.0 mm)

3-3/8”

(85.73 mm)

9-1/8”

(231.78 mm)

DATA HIGHWAY COMMUNICATION INTERFACE MODULE

Designed and Manufactured

For ALLEN-BRADLEY INDUSTRIAL COMPUTER GROUP CLEVELAND, OHIO USA

DYNAPRO SYSTEMS INC. VANCOUVER, B.C. CANADA

DATA HIGHWAY

MONITOR

CO.

DATA HIGHWAY COMPUTER

CATALOG NO.

1770-KF2

NO.

MODEL

Prototype

VOLTS

115/230V AC

SERIES REV.

NO.

SERIAL

Marketing

HERTZ

AMPS

0.30

50/60

ASYNCHRONOUS

DATE

June 10/86

MADE IN CANADA

10-3/8” (263.53 mm)

LM323K

∆τ

8428

WARNING

DISCONNECT POWER

BEFORE REMOVING

FUSE OR COVER

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Chapter 3

Installation

Mechanical Characteristics

The COMPUTER ASYNCHRONOUS connector on a KF2 module is a

male 25-pin D-shell. This connector conforms to the RS-232-C standard

and will accommodate any RS-232-C standard cable (see “Cabling”).

Electrical Characteristics

Selection of either RS-232-C or RS-422-A determines the input and

output levels of the transmit data and receive data circuits on the

asynchronous interface. When RS-232-C standard communication is

selected, all signals on the asynchronous interface are driven and received

by RS-232-C interface circuits which have a maximum drive capability of

50 cable-feet. When RS-422-A standard communication is selected, the

transmit and receive signals only are driven and received by RS-422-A

interface circuits which have a maximum drive capability of

4,000 cable-feet. In RS-422-A mode, all other signals except transmit and

receive still conform to RS-232-C.

The setting of Communication Option Switch 4 of Switch Group SW-1

determines whether the asynchronous port asserts the handshaking signals

or not (see “Asynchronous Link Features”). The handshaking signals are:

RTS, CTS, DSR, DCD, and DTR. When Switch 4 of SW-1 is ON, the

handshaking signals are used. When RS-422-A communications and

handshaking are both selected, handshaking signals are present; but they

conform to RS-232-C standards only.

Cabling

Cabling for the asynchronous port of the KF2 module will vary,

depending on your application and on whether you are using RS-232-C or

RS-422-A communications. The pinouts for the asynchronous connector

are as follows:

Signal Abbreviation RS-232-C RS-422-A

Protective Ground Transmitted Data Received Data Request to Send Clear to Send Data Set Ready Signal Ground Data Carrier Detect Data Terminal Ready Transmitted Data A Transmitted Data B Received Data A Received Data B

TXD RXD RTS CTS DSR GND DCD DTR TDA TDB RDA RDB

1 2 3 4 5 6 7 8

14 25 16 18

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Chapter 3

Installation

The definitions of the above signals are:

TXD carries serialized data. It is an RS-232-C standard output from

the module. RXD is RS-232-C standard serialized data input to the module. RTS is a request from the module to the modem to prepare to transmit.

With full-duplex protocol, RTS is always asserted. With half-duplex

protocol, it is turned on when the module has permission to transmit;

otherwise it is off. It conforms to RS-232-C specifications. CTS is a signal from the modem to the module that indicates the carrier

is stable and the modem is ready to transmit. The module will not

transmit until CTS is on. If CTS is turned off during transmission, the

module will stop transmitting until CTS is restored. It conforms to

RS-232-C specifications. DTR is a signal from the module to the modem to connect to the phone

line (i.e., “pick up the phone”). The module will assert DTR all the

time except during the phone hang-up sequence. Modems built to

American standards will not respond to DTR until the phone rings.

Some European modems will always pick up the phone, whether it is

ringing or not. The KF2 module will not work with these types of

European modems. DTR conforms to RS-232-C specifications. DSR is a signal from the modem to the module that indicates the phone

is off-hook. (It is the modem’s answer to DTR.) The module will not

transmit or receive unless DSR is on. If the modem does not properly

control DSR, or if no modem is used, DSR must be jumpered to a high

signal at the module’s asynchronous connector. (It can be jumpered to

DTR.) DSR conforms to RS-232-C specifications. DCD is a signal from the modem to the module to indicate that the

carrier from another modem is being sensed on the phone line. It will

not be asserted unless the phone is off-hook. Data will not be received

at the asynchronous connector unless DCD is on. With full-duplex

protocol, the module will not transmit unless DCD is on. If the modem

does not properly control DCD, or if a modem is not being used, DCD

must be jumpered to DTR at the module. DCD conforms to RS-232-C

specifications. TDA is the transmitted data signal for RS-422-A output from the

module. TDB is the differential return signal for TDA for transmitting

RS-422-A data. RDA is the RS-422-A data input to the module. RDB is the differential return signal for RDA.

If you are connecting a KF2 module to an RS-232-C compatible device (e.g., modem or computer), then you must mount the module within 50 cable-feet of that device. For such applications, the module’s GND

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Chapter 3

Installation

must be connected to the GND of the modem or computer. Note that this type of connection does not provide electrical isolation between the module and the connected device.

If a connection is made between the KF2 and an RS-422-A compatible device, you can mount the device and the module up to 4,000 cable-feet apart.

Direct Connection to a Computer

To connect the module directly to a computer, you can construct your own cable according to the wiring diagram in Figure 3.6.A. This cable plugs into the COMPUTER ASYNCHRONOUS connector on the module and the RS-232-C or RS-422-A compatible connector on the computer (Figure 3.6.A). Connect the cable shield at one end only. Be sure that the cable length does not exceed the RS-232-C limit of 50 feet or the RS-422-A limit of 4,000 feet.

Figure 3.6 Connection

A. Connection Diagram

B. W

iring Diagram for RS-232-C

Asynchronous Port Connector of 1770-KF2 Module (RS-232-C)

1 7

2 3 6

20 6

4 5

25-Pin Female Connector

3-12

25-Pin Female Connector 25-Pin Male Connector

Asynchronous Port Connector of 1770-KF2 Module (RS-232-C)

RS-232-C

Compatible Port

Connector of

Computer Cable (Not Exceeding 50 Feet)

25-Pin Male

Connector

to a Computer

Cable

Chassis Ground Signal Ground

7 3

RXD

TXD

DTR

DCD DSR

RTS CTS

RS-232-C or RS-422-A Port Connector of Computer

C. W

iring Diagram for RS-422-A

Asynchronous Port Connector of 1770-KF2 Module (RS-422-A)

1 14 25 16 18

8 20

25-Pin Female Connector

Compatible

Note:

The connector and the pinouts for the RS-422-A compatible computer port will depend on the computer manufacturer’ Other pins may have to be jumpered on the computer connector to ensure proper operation.

RS-422-A

Compatible Port

Connector of

Computer Cable (Not Exceeding 4,000 Ft.)

RDA RDB

TDA TDB

s standard assignment.

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Chapter 3

Installation

This type of connection includes the DTR signal to allow each end to detect the loss of the other end’s ability to communicate. If your computer does not provide the DTR signal, jump Pins 6 and 8 at the KF2 module to Pin 20.

Connection to a Modem

To connect the module to a modem, you can construct your own cable according to the wiring diagram in Figure 3.7. This cable plugs into the COMPUTER ASYNCHRONOUS connector on the module and the RS-232-C compatible connector on the modem (Figure 3.7). Connect the cable shield at one end only. Be sure that the cable length does not exceed the RS-232-C limit of 50 feet.

Figure 3.7 Connection

to a Modem

A. Connection Diagram

25-Pin Female Connector 25-Pin Male Connector

Asynchronous PORT

Connector of 1770-KF2 Module (RS-232-C)

B. W

iring Diagram

Asynchronous Port Connector

of 1770-KF2 Module (RS-232-C)

1 7

2 3 4

Cable

Cable (Not Exceeding 50 Feet)

RS-232-C Compatible Port Connector of Modem

RS-232-C

Compatible Port

Connector of

Modem

1 7

2 3 4

Chassis Ground Signal Ground

TXD RXD RTS

CTS

6 8

25-Pin Female

Connector

6 8

25-Pin Male

Connector

DSR DCD

DTR

14831

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Chapter 3

Installation

The module can be connected to standard American dial-up modems and some European modems. Other European standards specify that the DTR signal will make the modem answer the phone whether it is ringing or not, causing the phone always to be “busy.” Do not use the module with any type of modem that answers the phone when DTR is asserted, even while waiting for a call.

The types of dial-up network modems that you can use are:

Manual: These are typically acoustically coupled modems. The

connection is established by human operators at both ends, who insert the handsets into couplers to complete the connection.

DTE-Controlled Answer: These unattended modems are directly

connected to the phone lines. The module serves as the data terminal equipment to control the modem via the DTR, DSR, and DCD signals. The module incorporates timeouts and tests to properly operate these types of modems.

Auto-Answer: These modems have self-contained timeouts and tests

and can answer and hang up the phone automatically.

The module has no means of controlling an auto-dial modem, but it can be used in conjunction with a separate auto-dialer.

Connection to Another Communication Module

To learn about a direct RS-232-C communication link with a 1771-KE,

-KF, or -KG module, refer to Figure 3.8. To construct the cable, use a 25-pin female connector at the KF2 end and a 15-pin male connector at the other end.

To provide a direct RS-232-C link with a 1773-KA or a 1775-KA module, Figure 3.9, use a 25-pin female connector at the KF2 and a 25-pin male connector at the KA module.

Use Belden 8723 or equivalent cable (available from Allen-Bradley under Cat. No. 1778-CR). Connect the cable shield at one end only. You can make the cable up to 50 feet long.

3-14

Figure 3.8 Connection

A. Connection Diagram

to 1771-KG Module

Chapter 3

Installation

25-Pin Female Connector 15-Pin Male Connector

Asynchronous Port Connector of 1770-KF2 Module (RS-232-C)

B. W

iring Diagram

Asynchronous Port Connector of

1770-KF2 Module (RS-232-C)

1 7 2

3 4

5 6 8 8

25-Pin Female Connector

User-Supplied Connectors

User-Supplied Cable, Belden 8723, or Equivalent

(50 Feet Maximum) (Cat. No. 1778-CR)

User-Supplied Connectors

Connect the Shield at One End Only

User-Supplied Cable, Belden 8723, or Equivalent (50 Feet Maximum)

RS-232-C Port Connector of 1771-KE/KF or 1771-KG Module

RS-232-C

Port Connector

of 1771-KE/KF or

1771-KG Module

1 3

4 5 6

15-Pin Male

Connector

Chassis Ground RXD TXD

TDA RTS CTS DSR DCD

11697

3-15

Chapter 3

Installation

Figure 3.9 Connection to 1773-KA or 1775-KA Module

A. Connection Diagram

25-Pin Female Connector 25-Pin Male Connector

Asynchronous Port Connector of 1770-KF2 Module (RS-232-C)

B. W

iring Diagram

Asynchronous Port Connector

of 1770-KF2 Module (RS-232-C)

1 7 2

3 4

5 6 8 8

25-Pin Female Connector

User-Supplied Connectors

User-Supplied Cable, Belden 8723, or Equivalent

(50 Feet Maximum) (Cat. No. 1778-CR)

User-Supplied Connectors

Connect the Shield at One End Only

User-Supplied Cable, Belden 8723, or Equivalent (50 Feet Maximum)

RS-232-C

Port Connector

of 1773-KA

1775-KA

Module

25-Pin Male

Connector

RS-232-C Port Connector of 1773-KA 1775-KA

Chassis Ground

RXD TDB

TXD

Signal Ground

RTS

CTS

DSR DCD DTR

Module

11312

3-16

Answering

The module continually asserts DTR when it is waiting for a call. Under this condition, the modem will answer a call and assert DSR as soon as it detects ringing. The module does not monitor the RING indicator in the RS-232 interface. Once it detects DSR, the module starts a timer (around 10 seconds) and waits for the DCD signal. When the module detects DCD, communication can start.

If the module does not detect DCD within the timeout, the module turns DTR off. This causes the modem to hang up and break the connection. When the hang-up is complete, the modem turns off DSR. This causes the module to reassert the DTR line and wait for another call. This feature protects access to the phone if someone calling a wrong number reaches this station.

Chapter 3

Installation

After detecting DCD, the module continues to monitor the DCD line. If DCD goes off, the module restarts the timeout. If DCD is not restored within the timeout, the module initiates the hang-up sequence. This feature allows the remote station to redial in the event that the connection is lost through a fault in the phone network.

This handshaking is necessary to guarantee access to the phone line. If this handshaking protocol is defeated by improper selection of modem options or by jumpers at the connectors, the modem may still answer a call. But if the connection is lost, the modem will not hang up. It will then be impossible for the remote station to reestablish the connection because it will get a busy signal.

Character Transmission

The module sends data serially over the asynchronous interface, one 8-bit byte at a time. The transmission format conforms to ANSI X3.16, CCITT V.4, and ISO 1177, with the exception that the parity bit is retained while the data length is extended to eight bits.

The transmission format may be summarized as follows:

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 (optional) one stop bit

For communication rate see “Asynchronous Communication Rate and Diagnostic Commands” and for parity settings refer to “Asynchronous Link Features.”

3-17

Chapter 3

Installation

Diagnostic Indicators

There are 6 LED indicators on the front of a KF2 module (Figure 3.10). These indicators can help you in diagnosing problems with the module’s installation and operation. The indicators are:

PWR - Power On XMTG - Transmitting RCVG - Receiving RDY - Ready to Transmit ACTV - Active CPU - Module Fault, or DLE NAK Indicator

Figure 3.10 Diagnostic

(LED) Indicators

ALLEN–BRADLEY

DATA HIGHWAY COMMUNICATION INTERFACE

XMTG RCVG RDY ACTV CPUPWR

The XMTG light comes on when the KF2 module is current master of the network link and is transmitting a command or reply message.

The RCVG light comes on when the module is receiving a command or reply message from another station on the network link.

If the KF2 is on the Data Highway and the XMTG and RCVG lights are on at the same time, this indicates that the module is current master of the Data Highway and is polling the other stations to transfer mastership.

If the KF2 is on a PCL link and the XMTG and RCVG lights are on at the same time, this means that the module is determining whether there is a new module trying to access the link. This is known as “soliciting a successor.”

The RDY light comes on when the module has a message stored in its transmit buffer and it is waiting to acquire mastership of the network link so it can transmit the message.

3-18

Chapter 3

Installation

The ACTV light remains on as long as the cable between the COMPUTER ASYNCHRONOUS socket and the interfacing asynchronous device is properly connected. This light will appear to flicker whenever characters are being transmitted across the asynchronous link. If this light goes off, check the cable and connectors for possible problems.

The CPU light comes on for about half a second every time the module transmits or receives a DLE NAK protocol sequence (Chapter 4). If this light flickers frequently or stays on, the asynchronous link might need better isolation or noise immunity.

If the KF2 is on a PCL, the CPU light also flashes at about 1 Hz when a duplicate node (two stations with the same station number) is detected and stays on when an internal hardware fault is detected. For more on the KF2 self-diagnostics, see Chapter 1 under “Module Description.”

3-19

Chapter

Asynchronous Link Protocols

General

Definition of Link Protocol

This chapter describes the communication protocol used on the asynchronous link to the KF2 module. If you are connecting a KF2 module to another Allen-Bradley communication interface module (such as a 1771-KG, 1773-KA, or 1775-KA module), you need not be concerned with protocol because the modules automatically take care of it. However, if you are connecting a KF2 module to a computer, then you must program the computer to understand and to issue the proper protocol character sequences, as described in Chapters 4 through 6 of this manual.

A link consists of a wire and associated hardware—such as transceivers, UARTs, and error checkers. A link protocol carries a message error-free from one end of the link to the other, or it indicates failure with an error code. Internally it delimits messages, detects and signals errors, retries after errors, and controls message flow. It requires that the link hardware send characters from one end of the wire to the other.

The only purpose of a link protocol is to carry a message intact over a link. It has no concern for the content of the message, the message’s function in the operation of higher levels in the system, or the ultimate fate or purpose of the message. Once the message has been reliably carried from one end of the link to the other, the link protocol’s concern for that message is ended.

The asynchronous port of the KF2 module can use one of two link protocols, which are:

Full-Duplex Protocol (for Point-to-Point Communication) Half-Duplex Protocol (for Master-Slave Communication)

In general, full-duplex protocol gives faster data throughput but is harder to implement; half-duplex protocol is easier to implement but gives slower data throughput. Each of these protocols is described independently in “Full-Duplex Protocol” and “Half-Duplex Protocol” respectively.

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Chapter 4

Asynchronous Link Protocols

Important: Some Allen-Bradley documentation might refer to full-duplex and half-duplex protocols as DF1 and polled-mode protocols, respectively.

Full-Duplex Protocol

Full-duplex protocol conforms closely to ANSI X3.28-1976, combining features of Subcategories D1 (data transparency) and F1 (two-way simultaneous transmission with embedded responses).

Full-duplex protocol is used over a point-to-point link that allows two-way simultaneous transmission. It is relatively difficult to implement because it requires a system programmer to use interrupts and multi-tasking techniques. It is intended for high-performance applications where it is necessary to get the highest possible throughput from the available communication medium.

Transmission Codes

Full-duplex protocol is character-oriented; it uses the following ASCII control characters extended to eight bits by adding a zero for Bit 7. See ANSI X3.4, CCITT V.3, or ISO 646 for the standard definition of these characters.

Control

Character Hexadecimal Code

STX (Start of T ETX (End of T ENQ (Enquiry) ACK (Acknowledge) DLE (Data Link Escape) NAK (Negative Acknowledge)

ext) 02

ext) 03

05 06 10 15

4-2

The term “code” is defined for use in the following paragraphs as an indivisible sequence of one or more bytes having a specific meaning to the link protocol. “Indivisible” means that the component characters of a code must be sent one after another with no other characters between them. It does not refer to the timing of the characters.

The following codes are used in full-duplex protocol:

Control Codes:

- DLE STX

- DLE ETX BCC/CRC

- DLE ACK

- DLE NAK

- DLE ENQ

Chapter 4

Asynchronous Link Protocols

Data Codes:

- Data (single characters having values 00-0F and 11-FF hex)

- DLE DLE (to represent the value 10 hex)

Codes are grouped into two classes: message codes, sent from transmitter to receiver; and response codes, sent from receiver to transmitter.

DLE STX is a message code used to indicate the start of a message. DLE ETX BCC/CRC is a message code used to terminate a message. Data 00-0F and 11-FF hex are message codes used to encode the

corresponding values in the message itself. DLE DLE is a message used to encode the occurrence of the value 10 in the message.

DLE ENQ is a message code. It requests the retransmission of the last

received code.

DLE ACK, a response code, signals that a message has been

successfully received.

DLE NAK, also a response code, signals that an attempt to transfer a

message has failed.

Link-Layer Message Packets

A link-layer message packet starts with a DLE STX and ends in a DLE ETX BCC/CRC, with data codes in between. Data codes can occur only inside a message packet. Response codes can also occur between a DLE STX and a DLE ETX BCC/CRC, but such response codes are not part of the message packet. They are referred to as embedded responses.

Figure 4.1 shows the format of a link-layer message packet for full-duplex protocol, and the layer at which each portion should be implemented. At the end of each message packet is the one-byte BCC field.

4-3

Chapter 4

Asynchronous Link Protocols

Figure 4.1 Packet

Format for Full-Duplex Protocol

CMD STS Command/Response Block

DST SRC CMD STS TNS

DLE STX

Data

(From Network Layer)

Block Check

(From Application Layer)

Data

DLE ETX

BCC Data Link

From Application Layer

From Network Layer

Layer Packet

11321A

The block check character (BCC) is a means of checking the accuracy of each message packet transmission. It is the 2’s complement of the 8-bit sum (modulo-256 arithmetic sum) of all data bytes between the DLE STX and the DLE ETX BCC. It does not include any other message packet codes or response codes.

Example 1: If a message packet contained the data codes 08, 09, 06, 00, 02, 04 and 03, the message packet codes would be (in hex):

10 DLE STX

02 08 09 06 00 02 04 03 10 03 E0

DLE ETX BCCData

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Chapter 4

Asynchronous Link Protocols

The sum of the data bytes in this message packet is 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 hex 1101 1111 1’s complement +1 1110 0000 2’s complement (E0 hex)

Example 2: To transmit the data value 10 hex, you must use the data code DLE DLE. 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, you would use the following message codes:

Represents Single Data Byte Value of 10

10 DLE STX

02 08 09 06 00 10 10 04 03 10 03 D2

DLE ETX BCCData

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

The BCC algorithm provides a medium level of data security. It cannot detect transposition of bytes during transmission of a packet. It also cannot detect the insertion or deletion of data values of zero within a packet.

Cyclic Redundancy Check

Calculate the CRC value on the value of the data bytes and the ETX byte

(using the polynomial x

+ x15 + x2 + x0). To transmit the data value of 10 hex, you must use the data code DLE DLE. However, only one of these DLE data bytes is included in the CRC value. Embedded responses are not included in the CRC value.

At the start of a message packet, the transmitter clears a 16-bit register for the CRC value. As a byte is transmitted, it is exclusive-ORed (with Bit 0 to the right) to the right eight bits of the register. The register is then shifted right eight times with zeros (0s) inserted on the left. Each time a one (1) is shifted out on the right the following binary number is exclusive-ORed with the 16-bit register value:

4-5

Chapter 4

Asynchronous Link Protocols

1010 0000 0000 0001

As each additional byte is transmitted, it is included in the value in the register the same way. After the ETX value is included in the value in the register and is transmitted, the value in the register is transmitted (right bit first) as the CRC field.

The receiver also calculates the CRC value and compares it to the received CRC value to verify the accuracy of the data received.

Two-Way Simultaneous Operation

On a two-way simultaneous link there are only two physical circuits connecting 4 distinct and independent programs. Referring to the diagram below, Transmitter A and Receiver B manage the transfer of messages from Station A to Station B by sending message packets from A to B and returning responses from B to A. At the same time, Transmitter B and Receiver A carry out the transfer of messages from Station B to Station A by sending message packets from B to A and returning responses from A to B.

Figure 4.2 shows the four independent data paths involved.

Figure 4.2 Data

Paths for T

wo-W

Transmitter

Receiver

ay Simultaneous Operation

Path 1

Receiver

Path 2

Path 3

Transmitter

Path 4

11556

Path 1 carries message codes from A to B; Path 2 carries response codes from B to A; Path 3 carries message codes from B to A; and Path 4 carries response codes from A to B.

4-6

Chapter 4

Asynchronous Link Protocols

To implement all of these data paths with only two physical circuits, a software multiplexer combines the message codes with the response codes going in the same direction. At the other end of the link a software separator divides the message codes from the response codes. The message codes are sent to the receiver, and the response codes are sent to the transmitter via internal software. On each physical circuit, response codes from a receiver to a transmitter will be seen intermingled with message codes being sent from a transmitter to a receiver. Figure 4.3 shows this implementation.

Figure 4.3 Software

Implementation of Data Paths

Path 2

Path 3

Transmitter

Receiver

= Software Multiplexer

Path 1

Path 4

Physical Circuit AB

Physical Circuit BA

Receiver

Path 2

Path 3

Transmitter

S = Software Separator

Path 1

Path 4

11557

4-7

Chapter 4

Asynchronous Link Protocols

Figure 4.4 shows Path 1 with unrelated parts of Figure 4.3 removed.

Paths 2, 3, and 4 could be similarly shown.

Figure 4.4 Path

1, Unrelated Parts of Figure 4.3 Removed

Transmitter

Path 1 Path 1

Receiver

11558

The full-duplex protocol is symmetrical; that is, anything that can be said about Transmitter A, Receiver B, and Paths 1 and 2 applies equally to Transmitter B, Receiver A, and Paths 3 and 4. There are actually two independent instances of the protocol operating simultaneously. For simplicity the protocol will be defined on the subsystem that carries messages from A to B, with reference to Figure 4.5.

Figure 4.5 Message

Transmission from A to B

4-8

Transmitter

Path 2 Path 1 Path 2 Path 1

Path 1

Path 2

Receiver

11559

Chapter 4

Asynchronous Link Protocols

Although the protocols on each subsystem operate independently of each other, there will be a slight interaction as transmission of a message is delayed when a two-character response code is inserted in a stream of message codes. Also, any hardware problem that affects message codes traveling over a hardware circuit will also likely affect response codes on the same circuit.

Protocol Environment Definition

To fully define the environment of the protocol, the transmitter needs to know where to get the message it sends; and the receiver must have a means of disposing of messages. These are implementation dependent functions which shall respectively be called the message source and the message sink.

We assume that the message source supplies one message at a time upon request from the transmitter and requires notification of the success or failure of the transfer to Station B before supplying the next message. When the message source is empty, the transmitter waits in an inactive state until a message is available. Whenever the receiver has received a message successfully, it attempts to give it to the message sink. The possibility exists that the message sink will be full. The receiver requires an indication of this.

Figure 4.6 shows this representation of the protocol environment.

Figure 4.6 Protocol

Network Packet

SOURCE SINK

Status Path 2 Full

Transmitter

Environment

Path 1

Network Packet

Receiver

Software Software

Hardware

11560

4-9

Chapter 4

Asynchronous Link Protocols

Message Characteristics

Ideally the link protocol should not be at all concerned with the content or form of the message it is transferring. However, full-duplex protocol places the following restrictions on the messages that are submitted to it for transfer:

1. Minimum size of a valid message is 6 bytes, maximum is 250 bytes.

2. Some protocol implementations (point-to-point links to a 1771-KG

module, for example) require that the first byte of a message match the station address. The receiver will ignore messages that do not contain the correct address.

3. As part of the duplicate message detection algorithm, the receiver

checks the second, third, fifth, and sixth bytes of each message. There must be a difference in at least one of these bytes between a message and the previous one for it to be recognized as distinct rather than a retransmission of the previous message. If Switch 3 of Switch Group SW-1 if off, the KF2 module does not implement duplicate message detection (see Chapter 3, “Asynchronous Link Features”).

Protocol Definition

Whenever the message source can supply a message and the transmitter is not busy, it sends a message packet on Path 1. It then starts a timeout and waits for a response on Path 2.

When a DLE ACK is received, the message has been successfully transferred. After signaling the message source that the message has been sent, the transmitter proceeds with the next message.

If a DLE NAK is received, the message will be retransmitted. The transmitter restarts the timeout and waits again for a response. This can be repeated several times. There is a user-defined limit to the number of times a message can be retransmitted. If this limit is exceeded, the message source will be signaled of the failure; and the transmitter will proceed with the next message.

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Chapter 4

Asynchronous Link Protocols

If the timeout expires before a response is received, the transmitter sends a DLE ENQ on Path 1 to request a retransmission of the last response sent on Path 2. It restarts the timeout and waits for a response.

This too can be repeated several times, and there is a user-defined limit on the number of timeouts that are allowed per message. If the enquiry limit is exceeded, the message source will be signaled that the transmission has failed, and the transmitter proceeds to the next message.

Since there are only two response codes defined, there are no invalid response codes. If the separator returns an invalid response code, the transmitter will ignore it. A more precise and detailed description of the actions of the transmitter appears in Table 4.A in structured English procedures. Figure 4.7 is a flowchart of the software logic for implementing the transmitter.

Figure 4.7 Software

Legend:

Logic for Implementing T

Message Packet

DLE STX Data DLE ETX BCC

Received DLE ACK

Yes

P = Recovery Procedure

ransmitter

Retransmit Same Message

Received DLE NAK

Yes

NAKs

Received for this

Message

Yes

imeout Loop

Yes

Timed Out

Yes

Timeouts

for this

Message

= Ready to Transmit

Next Message

* Default Values Used

by the Module

DLE ENQ

11322

4-11

Chapter 4

Asynchronous Link Protocols

able 4.A

ransmitter for Full-Duplex Protocol

TRANSMITTER is defined as

loop

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

end loop

TRANSFER (Message) is defined as

initialize NAK-limit and ENQ-limit SEND (Message) start timeout 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 retries; SEND-MESSAGE (Message);

start timeout end end

else if timeout

if ENQ-limit is exceeded then return FAILURE else

begin

count ENQ retries;

send DLE ENQ on Path 1;

start timeout end end

end loop

4-12

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 code 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.

Chapter 4

Asynchronous Link Protocols

Receiver Actions

Since the receiver gets “dirty” input from the physical world, it is more complex and must be capable of responding to many adverse situations. Some of the things that can conceivably happen are listed here:

1. The message sink can be full, leaving the receiver with nowhere to

put a message.

2. A message can contain a parity error.

3. The BCC can be invalid.

4. The DLE STX or DLE ETX BCC may be missing.

5. The message can be too long or too short.

6. A spurious control or data code can occur outside a message.

7. A spurious control code can occur inside a message.

8. The DLE ACK response can be lost, causing the transmitter to send a

duplicate copy of a message that has already passed to the message sink.

A record of the last response sent on Path 2 is kept. The value of this response is either ACK or NAK. It is initialized to NAK. When a DLE ENQ is received, the receiver sends the value of the last response from this variable.

A record is kept of several message header bytes. If a message has the same header as the previous message, the message is ACKed but discarded.

The receiver ignores all input from Path 1 until a DLE STX or a DLE ENQ is received. If anything other than a DLE STX or DLE ENQ is received on Path 1, the receiver sets the last response variable to a NAK.

If an ENQ is received, the last response is sent on Path 2; and the receiver continues waiting for input.

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Chapter 4

Asynchronous Link Protocols

If a DLE STX is received, the BCC and the message buffer are reset; and the receiver starts building a message.

While building a message, all data codes are stored in the message buffer and added to the BCC. If the buffer overflows, the receiver continues summing the BCC, but the data is discarded. If a parity, overrun, framing, or modem handshaking error is detected, it is recorded. If any control codes other than a DLE EXT BCC are received, the message is aborted and a DLE NAK sent on Path 2. When the DLE ETX BCC is received, the error flag, the BCC, the message size, and the address (optionally) are all checked. If any of the tests fail, a DLE NAK is sent on Path 2.

If the message is OK, its header is compared to the last message. If it is the same, the message is discarded; and a DLE ACK is sent. (Duplicate message detection is not implemented if Switch 1 of Switch Group SW-1 is turned off.)

If the message is different from the last one, the state of the message sink is tested. If the message sink is full, a DLE NAK is sent; otherwise the message is forwarded to the message sink; the header information is saved for the duplicate message detector; and a DLE ACK is sent.

The procedure for the 1771-KC/KD and 1771-KG (Revision C) modules is different. First, they check the message sink state. If the sink is full, the response is recorded but not sent. The receiver waits for a DLE ENQ on Path 1. If any other code is received, the response is changed from ACK to NAK and the receiver continues waiting for a DLE ENQ. If a DLE ENQ is received, the sink status is checked. If it is still full, the receiver continues waiting. If it is not full, the last response is sent; and the receiver then accepts new messages. This variation is not documented in the structured English section found in Table 4.B.

The receiver for the KF2 module is listed in Table 4.B in structured English. Figure 4.8 is a flowchart of the software logic for implementing the receiver.

4-14

able 4.B

Receiver

Chapter 4

Asynchronous Link Protocols

for Full-Duplex Protocol

RECEIVER

GET

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-CODE if DLE STX then

begin

BCC = 0 GET-CODE while it is a data code

begin

if buf

fer is not overflowed put data in buf

GET-CODE

end if the control code 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 last header

end

end else if DLE ENQ then send LAST else LAST

end loop

-CODE is defined as

loop

-CHAR is defined as

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

-RESPONSE = NAK

GET-CHAR if char is not a DLE

begin

add char to BCC return the char and 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 ACK or NAK send it to the transmitter else if char is an ETX

begin

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

end else return character with a control flag

end

end loop

-RESPONSE

fer

4-15

Chapter 4

Asynchronous Link Protocols

Figure 4.8 Receiver

for Full-Duplex Protocol

RCVE

LAST = NAK

Receive DLE ENQ ?

Receive Message ?

Yes

BCC/CRC OK ?

Yes

LAST = ACK

Yes

LAST = NAK

4-16

Send DLE LAST

11699

Chapter 4

Asynchronous Link Protocols

Full-Duplex Protocol Diagrams

The following figures show some events that can occur on the various interfaces. Time is represented as increasing from the top of the figure to the bottom. Data bytes are represented by “xxxx”; corrupted data by “???”.

Figure 4.9 Normal

Message T

SOURCE XMTR LINK RCVR SINK

xxxx

DLE STX xxxx DLE ETX BCC

ransfer

Not Full

DLE ACK

Figure 4.10 Message T

SOURCE XMTR LINK RCVR SINK

xxxx

DLE STX x??x DLE EXT BCC

DLE STX xxxx DLE ETX BCC

ransfer with NAK

DLE NAK

xxxx

11561

Not Full

xxxx

DLE ACK

11562

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Chapter 4

Asynchronous Link Protocols

Figure 4.1 Message T

SOURCE XMTR LINK RCVR SINK

xxxx

DLE STX xxxx DLE EXT BCC

(Timeout)

ransfer with Timeout and ENQ

??? CK

DLE ENQ DLE ACK

Not Full

xxxx

Figure 4.12 Message T

ransfer with Retransmission

11563

SOURCE XMTR LINK RCVR SINK

xxxx

DLE STX xxxx DLE EXT BCC

Not Full

xxxx

??? CK

???

(Timeout)

DLE ENQ

DLE NAK

DLE STX xxxx DLE EXT BCC

DLE ACK

Note that this is detected as a duplicate message.

(Message Discarded)

11564

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Chapter 4

Asynchronous Link Protocols

Figure 4.13 Message T

SOURCE XMTR LINK RCVR SINK

xxxx

DLE STX xxxx DLE EXT BCC

DLE STX xxxx DLE ETX BCC

ransfer with Message Sink Full

Full

DLE NAK

Full

DLE NAK

DLE STX xxxx DLE EXT BCC

Not Full

xxxx

DLE ACK

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Retransmission occurs when noise hits both sides of the line. This type of noise destroys the DLE ACK while also producing invalid characters at the receiver. The result is that the receiver changes its last response to NAK and the transmitter retransmits the original message. Note that this is detected as a duplicate message if Switch 1 of Switch Group SW-1 is on.

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Asynchronous Link Protocols

Examples

If a line monitor were connected to the wires between Stations A and B, and only the A to B subsystem were active, the following would be observed:

Normal Message

Path 1:

Message with Parity or BCC Error and Recovery

Path 2: DLE ACK

Message with ETX Destroyed

Path 1: Path 2: DLE NAK DLE ACK

Good Message but ACK Destroyed

Path 1: Path 2:

Messages Being Sent in Both Directions

Path 1: Path 2: Path 3: Path 4:

DLE STX ... DLE ETX BCC

DLE ACKPath 2:

DLE STX ...xxx.. DLE ETX BCC

DLE STX .....xxxx [timeout] DLE ENQ

DLE STX ... DLE ETX BCC

DL xxx CK

DLE STX ... DLE ETX BCC DLE STX .... DLE ETX BCC

DLE ACK DLE ACK

DLE STX ...

DLE STX .... DLE ETX BCC

DLE STX .... DLE ETX BCCPath 1:

DLE NAK

DLE STX .... DLE ETX BCC

[timeout] DLE ENQ DLE STX ... etc.

DLE ACK

DLE STX

DLE STX.... DLE ETX BCC

DLE ACK

4-20

Combined

DLE STX ... DLE ETX BCCCircuit AB: DLE STX .... DLE ETX BCC DLE ACK DLE STX

Circuit BA: DLE STX ... DLE ACK .... DLE ETX BCC DLE ACK DLE STX

Embedded Response ACK on AB delayed slightly because ETX BCC are indivisible.

Embedded Response Option

To simplify the design of the receiver, you can, in some cases, disable transmission of embedded responses by turning off communication option Switch 2 of Switch Group SW-1. If this switch is OFF, the KF2 module’s multiplexer will not allow response codes to be sent within a message. Instead, it will delay response codes until after it receives the next DLE ETX BCC.

Chapter 4

Asynchronous Link Protocols

Half-Duplex Protocol

Half-duplex protocol is the alternative to full-duplex protocol. You can select half-duplex protocol by setting communication option Switches 1, 2, and 5 of SW-1. Half-duplex protocol is based on full-duplex but extends or redefines several features.

Half-duplex protocol is a multi-drop protocol for one master and one or more slaves. Modems must be used (unless there is only one slave). KF2 modules have slave mode capability only; the master function must be provided by a user-programmed intelligent device.

Half-duplex protocol provides a lower effective utilization of resources than full-duplex, but it is much easier to implement. Its use is indicated by the following:

Multiple stations and a single computer are connected in a multi-drop

configuration using multi-drop modems. Half-duplex modems are being used. It is desirable to sacrifice throughput in exchange for ease of

implementation.

Half-duplex protocol requires the following communication characteristics:

8 Bits per Character Even Parity 1 Stop Bit Pass-All Mode (The terminal driver does not translate or respond to

control characters.) Single Character Buffer (The terminal driver immediately returns each

character to the caller.)

Multi-Drop Topology

The intended environment for half-duplex protocol is a multi-drop link with all stations interfaced through half-duplex modems. The actual nature of the link does not matter much, as long as the modems support request-to-send, clear-to-send, and data-carrier-detect signals. If dial-up modems are used, they must also support data-set-ready and data-terminal-ready; otherwise, DSR should be jumpered to DTR.

There may be from 2 to 256 stations simultaneously connected to a single link. Each station has a receiver permanently connected to the circuit and a transmitter that may be enabled or disabled by RTS.

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Asynchronous Link Protocols

One station is designated as master, and it controls which station has access to the link. You can use a 1771-KGM PLC-2 Family module as the master, or this function can be performed by your own programmed intelligent device. All other stations are called slaves and must wait for permission from the master before transmitting. Each slave station has a unique station number from 0 to 254.

The master can send and receive messages to and from each station on the multi-drop. The master can send and receive messages to and from every station on highways that are connected to the multi-drop via a KF2 module. If the master is programmed to relay messages, then stations on the multi-drop can engage in peer-to-peer communications. The multi-drop will not easily provide flexible peer-to-peer communication between the multi-drop and connected highways, or between different highways.

Either a two-circuit system (master sends and slaves receive on one circuit, slaves send and master receives on the other), or a one-circuit system (master and slaves send and receive on the same circuit) can be used.

Half-duplex dial-up modems can be used as long as a carrier is detected before the carrier timeout (about 8 seconds). If a carrier is not sensed before the timeout, the module will hang up the phone. Carrier must be sensed at least every 8 seconds to maintain the connection.

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.

Transmission Codes

Half-duplex protocol is a character-oriented protocol that uses the following ASCII control characters extended to 8 bits by adding a zero for Bit 7. See ANSI X3.4, CCITT V.3, or ISO 646 for the standard definition of these characters.

4-22

Control

Character Hexadecimal Code

SOH (Start of Header) STX (Start of T ETX (End of T EOT (End of T ENQ (Enquiry) ACK (Acknowledge) DLE (Data Link Escape) NAK (Negative Acknowledge)

ext)

ransmission)

01 02 03 04 05 06 10 15

Chapter 4

Asynchronous Link Protocols

The term “code” means (in the following paragraphs) an indivisible sequence of one or more bytes having a specific meaning to the link protocol. “Indivisible” means that the component characters of a code must be sent one after another with no other characters inserted between them. It does not refer to the timing of the characters. (This definition has less significance than for full-duplex protocol since there is no multiplexing of transmission codes in half-duplex protocol.)

These codes are used in half-duplex protocol:

Control Codes:

- DLE SOH

- DLE STX

- DLE ETX BCC/CRC

- DLE ACK

- DLE NAK

- DLE ENQ

- DLE EOT

Data Codes:

- DATA (single characters having values 00-0F and 11-FF hex)

- DLE DLE (to represent the value 10 hex)

DLE SOH indicates the start of a message.

DLE STX separates the link level header from the data field of a message.

DLE ETX BCC/CRC terminates a message.

DATA 00-0F and 11-FF encode the corresponding values in the message itself. DLE DLE encodes the occurrence of the value 10 in the message.

DLE ACK signals that a message has been successfully received.

DLE NAK is used as a global link reset command and can be issued only by the master. It causes all slaves to cancel all messages that are ready to be transmitted to the master. Typically the slave will return the messages to the command originator with an error code.

DLE ENQ starts a poll command.

DLE EOT is used by slaves as a response to a poll when they have no messages to send.

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Chapter 4

Asynchronous Link Protocols

Link-Layer Packets

Half-duplex protocol uses three types of transmissions:

Polling Packet Master Message Packet Slave Message Packet

The master station transmits both polling packets and master message packets, while slave stations transmit slave message packets.

Figure 4.14 illustrates the formats of these packets. Note that the slave message packet has the same format as the full-duplex message packet (see “Link-Layer Message Packets”). The master message packet is the same as the slave message packet except that it is prefixed with DLE SOH and an address code to specify a slave station number.

Figure 4.14 Packet

Formats for Half-Duplex Protocol

A. Polling Packet

B. Slave Message Link Packet

CMD STS Command/Response Block

DST SRC CMD STS TNS

DLE STX

C. Master Message Link Packet

Data

(From Network Layer)

CMD STS

DLE ENQ STN BCC

Data

(From Application Layer)

DLE ETX

Command/Response Block

BCC

From Application Layer

From Network Layer

Data Link Layer Packet

From Application Layer

4-24

DST SRC CMD STS TNS

DLE SOH STN DLE STX

Data

(From Network Layer)

(From Application Layer)

Data

DLE ETX

BCC

From Network Layer

Data Link Layer Packet

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Asynchronous Link Protocols

At the end of each polling packet there is a BCC byte. At the end of each message packet, there is either a one-byte BCC field or a two-byte CRC field. You can select BCC or CRC through switch settings (see Chapter 3, “Asynchronous Link Features”).

Block Check

The block check character (BCC) is a means of checking the accuracy of each packet transmission. It is the 2’s complement of the 8-bit sum (modulo-256 arithmetic sum) of the slave station number (STN) and all the data bytes in the packet. For polling packets, the BCC is simply the 2’s complement of STN. The BCC does not include any other message packet codes or response codes.

Example 1: If the master station wanted to send the data codes 08, 09, 06, 00, 02, 04, and 03 to Slave Station 20 hex (40 octal), the master message codes would be (in hex):

DLE SOH

20 STN

DLE10STX

08 09 06 00 02 04 03 10 03 C0

DLE ETX BCCData

The sum of the STN and data bytes in this message packet is 40 hex. The BCC is the 2’s complement of this sum, or C0 hex. This is shown in the following binary calculation:

0100 0000 40 hex 1011 1111 1’s complement +1 1100 0000 2’s complement (C0 hex)

Example 2: To transmit the STN or data value 10 hex, you must use the data code DLE DLE. However, only one of these DLE text characters is included in the BCC sum. For example, to transmit the values 08, 09, 06, 00, 10, 04, and 03 hex, a slave station would use the following message codes:

Represents Single Text Value of 10

02 08 09 06 00 10 10 04 03 10 03 D2

DLE STX

DLE ETX BCCData

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Chapter 4

Asynchronous Link Protocols

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

Cyclic Redundancy Check

Calculate the CRC value on the value of the data bytes and the ETX byte

(using the polynomial x

At the start of a message packet, the transmitter clears a 16-bit register for the CRC value. As a byte is transmitted, it is exclusive-ORed (with Bit 0 to the right) to the right eight bits of the register. The register is then shifted right eight times with zeros (0s) inserted on the left. Each time a one (1) is shifted out on the right, the following binary number is exclusive-ORed with the 16-bit register value:

1010 0000 0000 0001

The receiver also calculates the CRC value and compares it to the received CRC value to verify the accuracy of the data received.

Important: In half-duplex mode there is a BCC on the polling packet regardless of whether BCC or CRC error checking is used on messages.

4-26

Master/Slave Transceiver

In each station there is a program associated with the physical link called the transceiver. The master station has a more complex transceiver than the slave, since it must include a polling algorithm. The slave’s

Chapter 4

Asynchronous Link Protocols

transceiver is illustrated in Figure 4.15, and the master transceiver is illustrated in Figure 4.16.

To fully define the environment of the protocol, the transceiver needs to know where to get the messages it sends and must have a means of disposing of messages it receives. These are implementation-dependent functions that shall respectively be called the message source and the message sink.

We assume that the message source will supply one message at a time upon request from the transceiver and will require notification of the success or failure of transfer before supplying the next message.

When the transceiver has received a message successfully, it will attempt to give it to the message sink. The possibility exists that the message sink will be full. The transceiver requires an indication of this.

Figure 4.15 Slave Transceiver

Network Packet

SOURCE SOURCE

OK OK

Network

SINK SINK

Packet

Full

Software Software

MASTER

TRANSCEIVER

Link

SLAVE

RECEIVER

To Other Slaves

Hardware

Network Packet

Full

Message Characteristics

Ideally, the link protocol should not be at all concerned with the content or form of the messages it is transferring. However, half-duplex protocol places the following restrictions on the messages that are submitted to it for transfer:

11566

1. Minimum size of a valid message is 6 bytes, maximum is 250 bytes.

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Chapter 4

Asynchronous Link Protocols

2. Some protocol implementations require that the first byte of a

message match the station address. These receivers will ignore messages that do not contain the correct address. This filtering is not required, since the message sink can also provide the address filtering function.

3. As part of the duplicate message detection algorithm, the receiver

checks the second, third, fifth, and sixth bytes of each message. There must be a difference in at least one of these bytes between a message and its predecessor for it to be recognized as distinct rather than a retransmission of the previous message.

Master Polling Responsibilities

The master polling algorithm may vary depending on the expected flow of traffic through the system.

A simple master that does not expect unsolicited messages continuously polls each slave once in a round-robin fashion. If a message is received, it should be handled, then the next station polled. An alternative scheme would poll each station repeatedly until it was empty and then proceed to the next. Relaying of peer-to-peer messages is best left to the network layer, which is the lowest level of the body of software that includes the message source and sink.

Figure 4.16 is a flowchart of the software logic for implementing half-duplex protocol from the master station’s point of view.

4-28

XCVR

Select Station

Figure 4.16 Half-Duplex

Master T

Chapter 4

Asynchronous Link Protocols

ransceiver

Poll Selected Station

Start Timeout

Receive DLE EOT

Yes

Set Active Station Flag

Network Layer has Message to

send?

Yes

Get Message from

Network Layer

Send Message

Station to Poll Is Master?

Send Poll

YesNo

Receive

Message

Active Station

Yes

Message

OK?

Yes

Duplicate Message

Create Master Message

Is Message for Master

Yes

Start Timeout

Receive

DLE ACK

Timeouts

for this

Message?

Tell Network Layer

of Failure

Send to Network Layer

Yes

Timeouts

for this Poll?

Remove Station from Active List

Send Message to Destination

Yes

Send DLE ACK

Yes

11698

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Chapter 4

Asynchronous Link Protocols

Slave Transceiver Actions

Since the transceiver receives “dirty” input from the physical world, it must be capable of responding to many adverse situations. Some of the things that could conceivably happen are listed below:

1. The message sink can be full, leaving nowhere to put a message.

2. A message can contain a parity error.

3. The BCC can be invalid.

4. The DLE SOH, DLE STX, or DLE ETX BCC may be missing.

5. The message can be too long or too short.

6. A spurious control or data code can occur outside a message.

7. A spurious control code can occur inside a message.

8. The DLE ACK response can be lost, causing the transmitter to send a

duplicate copy of a message that has already been passed to the message sink.

The slave is always in a passive mode until it receives a message. While waiting for a message, anything besides the DLE SOH or DLE ENQ is ignored. Note that in a single circuit system the slaves must be able to safely ignore everything sent by other slaves.

If a DLE SOH is received, the BCC and the message buffer are reset. The next code received must be a data code and must equal the station address or 255 (if the station can receive broadcast messages). If there is no match, the station ignores the rest of the message and continues waiting for the start of the message.

4-30

If the station address matches, it is added to the BCC. The next code is received and must match DLE STX. If it doesn’t, the station ignores the rest of the message. Otherwise it starts building a message.

While building a message, all data codes are stored in the message buffer and added to the BCC. If the buffer overflows, the receiver continues

Chapter 4

Asynchronous Link Protocols

summing the BCC, but the data is discarded. If an error is detected, it is recorded. If any control code other than a DLE ETX BCC is received, the error flag, the BCC, the message size, and the address (optionally) are all checked. If any of the tests fail, the message is ignored.

If the message is OK, its header is compared to the last message. If it is the same, the message is discarded and a DLE ACK is transmitted. If it is different, the new header is saved and the message is sent to the message sink. If the message can be stored, a DLE ACK is sent. If the message sink is full, the message is discarded and not acknowledged.

If while waiting for a message a DLE ENQ is received, the transceiver accepts the next two characters. The last character is read directly from the link, since it is a BCC and is not byte stuffed. If the station address does not match or there is an error, the poll is ignored. If the poll is accepted, there are three possible situations:

1. The transceiver could still be holding a message that it had

transmitted previously but had not been ACKed. There is a limit on the number of times each message can be sent. If this limit is exceeded when the poll is received, the message is returned to the message source with an error indication, and the transceiver tries to send the next message from the message source. If the limit is not exceeded, the response to the poll will be to resend the current message.

2. If no message is currently being held, the transceiver tries to get one

from the message source. If one is available, the transceiver will initialize its retry counter and transmit it in response to the poll.

3. If no message is available, the response to a poll will be to transmit a

DLE EOT.

When a message is transmitted after receiving a poll, its format is identical to a full-duplex message packet. After sending a message, the transceiver will hold the message until a DLE ACK is received, or the number of times the message has been polled exceeds the limit.

When a DLE ACK is received, the message currently held is discarded. When the next poll is received, the next message available from the message source is sent (or a DLE EOT).

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When a DLE NAK is received, the transceiver takes messages from the source until it is empty. Each message will be discarded with an error code sent back to the message source. This can be used by the master to clear up the message source buffers of all slaves after the master has been down.

Half-Duplex Protocol Diagrams

The following figures show some of the events that occur on various interfaces. Time is represented as increasing from the top of the figure to the bottom.

Figure 4.17 Normal

Message T

ransfer

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

xxxx

DLE SOH STN

DLE STX xxxx DLE ETX BCC

Not Full

xxxx

DLE ACK

Figure 4.18 Message T

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

xxxx

DLE SOH STN

ransfer with Invalid BCC

DLE STX ??? DLE ETX BCC

11567

4-32

(Timeout)

DLE STX xxxx DLE ETX BCCDLE SOH STN

Not Full

xxxx

DLE ACK

11568

Chapter 4

Asynchronous Link Protocols

Figure 4.19 Message T

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

xxxx

(Timeout)

ransfer with ACK Destroyed

DLE STX xxxx DLE ETX BCCDLE SOH STN

Not Full

xxxx

DL ??? CK

DLE STX xxxx DLE ETX BCCDLE SOH STN

DLE ACK

11569

Figure 4.20 Poll with No Message A

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

Not Full

DLE EOT

vailable

BCCDLE ENQ STN

No Message

11570

Figure 4.21 Poll with Message Returned

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

Not Full

BCCDLE ENQ STN

xxxx

DLE STX xx???xx DLE ETX BCC

xxxx

BCCDLE ENQ STN

DLE STX xxxx DLE EXT BCC

DLE ACK

Same Message

11571

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Chapter 4

Asynchronous Link Protocols

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

Not Full

xxxx

Sometime Later ...

Not Full

Figure 4.22 Duplicate Message T

DLE STX xxxx DLE ETX BCC

ransmission

BCCDLE ENQ STN

DL ??? CK

BCCDLE ENQ STN

xxxx

DLE ACK

(Discard Retransmission)

Figure 4.23 Message Sink Full, Case 1

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

xxxx

DLE STX xxxx DLE ETX

(Timeout)

Not Full

BCCDLE ENQ STN

DLE EOT

Sometime Later ...

BCCDLE SOH STN

Full

No Message

11572

4-34

BCCDLE SOH STN DLE STX xxxx DLE ETX

Not Full

xxxx

DLE ACK

11573

Chapter 4

Asynchronous Link Protocols

Figure 4.24 Message Sink Full, Case 2

SOURCE/ SOURCE/ SINK MASTER LINK SLAVE SINK

xxxx

Not Full

xxxx

(Timeout)

DLE STX xxxx DLE ETX

DLE STX

xxxx DLE ETX BCC

DLE ACK

BCCDLE ENQ STN

BCCDLE SOH STN

Full

xxxx

BCCDLE SOH STN DLE STX xxxx DLE ETX

Not Full

xxxx

DLE ACK

11575

The message sent for the second poll is the same as the first, since the first transmission was not ACKed. Also, the master should ACK and discard the second message, since it was a retransmission. This means that the master must either poll a station repeatedly until it receives a DLE EOT, without polling any other stations, to be sure it has detected all retransmissions.

If each station is polled only once per cycle, the master must keep a record of the last header from each station, since other stations may transfer messages between retransmissions from a station.

When a station times out, it is a good idea to poll it to see if it is there. If it answers with a DLE EOT to a message, but consistently fails to a ACK a message, its message sink is probably full. If it responds DLE EOT to a poll, you must wait for the buffers to clear.

When a station’s message source and sink share a common memory pool, it may be that the message sink “full” indication results from an abundance of messages in the message source, which use up all free pool memory. In this case, the memory can be freed up by receiving messages from the station. Waiting for the memory to clear by the action of the

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Chapter 4

Asynchronous Link Protocols

station alone may not work, since it could be that the only way to free up space is to send a message to the master.

Line Monitoring

When monitoring half-duplex protocol in two-wire mode, you need to monitor only one line. The example below shows a message sent by the master and a reply sent by the slave in answer to a poll. Slave responses are in boldface.

Message from Master to Slave:

DLE SOH STN DLE STX message DLE ETX BCC DLE ACK

Message Sent from Slave to Master in Response to Poll:

DLE ENQ STN BCC DLE STX message DLE ETX BCC DLE ACK

Poll with a DLE EOT in Response:

DLE ENQ STN BCC DLE EOT

4-36

Message Packet Formats

Chapter

General

Application Layer

This chapter describes how your computer application programs should format command and reply messages for transmission over the asynchronous link. It covers both application level and network level functions. Basically, the application layer specifies the contents of messages and initiates their transmissions. The network layer takes the information from the application layer and formats it in a way that is acceptable to the data link layer (Chapter 4).

There are two types of application programs: command initiators and command executors. These names correspond with the two message types:

Command Messages — Sent by command initiators to command

executors.

Reply Messages — Sent by command executors in response to

command messages received from command initiators.

Each command message requires one reply message.

Command initiators specify which command function to execute at a particular destination station. The command executor at that destination station is responsible for interpreting the command message and executing the specified command function. The command executor also issues a reply message for each command it receives. If it cannot execute the received command, the command executor must generate the appropriate error message.

Network Layer

Internally, the KF2 module uses a routing subroutine and a message queue to implement the network layer. When the module receives a message over its asynchronous port, it puts that message in the queue. The routing subroutine then takes the message from the queue and transmits it over the Data Highway link. The module also queues messages received from the Data Highway, and the routing subroutine retransmits those messages over the asynchronous link. Figure 5.1 illustrates this model.

5-1

Chapter 5

Message Packet Formats

Figure 5.1 Network

Model

Command

Initiator

Commands

Replies

Network

RQ= Routing Subroutine Entry = Incoming Message Queue

Replies

Command

Executor

Commands

11576

Messages do not necessarily arrive at their destination in the same order that they were sent. It is impossible for the network layer to guarantee delivery, and in some cases it may not be possible to provide notification of non-delivery.

5-2

In particular, the network layer does not notify the command executor about non-delivery of a reply message. Therefore, it is advisable that your command initiator maintain a timer for each outstanding command message. If the time limit expires before the command initiator receives the corresponding reply to its command, it can either retransmit the same command message or indicate an error condition.

If your network layer software cannot deliver a command message, it should generate a reply message with an error code in it and send that reply to the command initiator. If it cannot deliver a reply message, the network layer software should simply destroy the reply without notification to the command executor.

If your link layer software cannot deliver a message over the asynchronous link, it also should return an error message to the command initiator.

Chapter 5

Message Packet Formats

Message Packets

The message bytes contain unsigned binary data from both the application layer and the network layer. Figure 5.2 shows the general format of a command message.

Figure 5.2 Command

DST SRC CMD STS TNS

Message Packet Format

CMD STS FNC

(0)

Legend: x = low hex digit of CMD byte supplied by application layer

ADDR

Command Block

SIZE OR DATA0

From Application Layer

Network Layer Packet

11329A

Not all command messages have FNC, ADDR, SIZE, or DATA bytes.

Figure 5.3 shows the general format of a reply message. The definitions of these bytes are the same as those for command messages. Not all reply messages have DATA or EXT STS bytes.

Figure 5.3 Reply

Message Packet Format

CMD STS DATA

DST SRC CMD STS TNS

Legend: x = low hex digit of CMD byte supplied by application layer

EXT STS

Response Block

(From Application Layer)

Note that the bytes are shown from left to right in the order in which they are transmitted across the link.

From Application Layer

Network Layer Packet

11330A

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Chapter 5

Message Packet Formats

The meanings of the bytes are:

DST — Destination Station for the Message SRC — Source Station of the Message CMD — Command Code STS — Status Code TNS — Transaction Number (2 Bytes) FNC — Function Code EXT STS — Extended Status Code ADDR — Address of Memory Location (2 Bytes Minimum) SIZE — Number of Bytes to Be Transferred DATA — Data Values Being Transferred by the Message

These bytes are described in more detail below.

DST and SRC

The DST (destination) byte contains the station number of the station that is the ultimate destination of the message. The SRC (source) byte is the station number of the station that originated the message.

The network layer supplies the DST and SRC values. Allowed values for these bytes are 0 to 254 decimal (0 to 376 octal). Note that you can form the DST and SRC bytes of a reply message simply by interchanging the DST and SRC bytes of the corresponding command message.

In application programming of a computer connected to the network by a KF2, the SRC byte should be set to zero. The module will set the byte to its own station number.

CMD and FNC

The CMD (command) and FNC (function) bytes together define the activity to be performed by the command message at the destination station. CMD defines the command type; and FNC, if used, defines the specific function under that command type.

5-4

Table 5.A lists all the available CMD and FNC codes in hexadecimal notation. The exact format for a particular message depends on the CMD and FNC values. “Message Formats” explains the use of each command or function and gives a detailed description of the message text format for each.

Chapter 5

Message Packet Formats

Figure 5.4 shows the format for the CMD byte itself. Bits 0 through 3 contain the command code. Bits 4 and 7 should always be set to 0. Bit 5 is the priority indicator; set to 0 for normal priority messages and 1 for high priority messages (Chapter 2). Bit 6 is the command/reply indicator; set it to 0 in a command message and 1 in a reply message.

Figure 5.4 CMD

Byte Format

76543210Bit 0 r p 0 command

11702

Reply messages also contain a CMD byte. To form the CMD value for a reply, the network layer copies the CMD value from the corresponding command message and sets the reply bit (Bit 6) to 1.

The application layer supplies the FNC value and the command code (Bits 0 to 3) of the CMD byte for each command message. The network layer supplies Bits 4 through 7 of the CMD byte.

STS and EXT STS

The STS (status) and EXT STS (extended status) bytes indicate the status of the message transmission. In command messages, the application program should always set the STS value to 0. In reply messages, the STS byte may contain one of the status codes listed in Chapter 7. If the four high bits of that byte are 1s (0F hex), there is extended status information in an EXT STS byte. Otherwise, there is no EXT STS byte. Note that an STS value of 0 in a reply message means “no error.”

In a reply message, the STS byte is divided between application layer and network layer. The network layer uses Bits 0 through 3 of the STS byte to report local errors (those errors that occur when the network layer attempts to transmit a message across the link).

The application layer uses Bits 4 through 7 of the STS byte (and in some cases the EXT STS byte), to report remote errors (those errors that occur when the command executor at the destination station tries to execute the command message). Chapter 7 explains local and remote error codes.

5-5

Chapter 5

Message Packet Formats

TNS

A complete transaction consists of a command message transmitted by a PC station. The TNS (transaction) bytes contain a a unique 16-bit transaction identifier. The first byte, RNG, contains the number of the PC program rung that generated the command; and the second, SQN, contains the transmission sequence number. For command messages transmitted by your computer station, your application programs can use the RNG and SQN bytes together to store a single 16-bit transaction number.

For command messages transmitted by a PC station, the station interface module assigns the TNS values. For each command message transmitted by your computer station, your network level software must assign a unique 16-bit transaction number; and a simple way to generate this number is to maintain a 16-bit counter at the network layer. Increment the counter every time your command initiator (application program) creates a new message and store the counter value in the two TNS bytes of the new message.

When the command initiator receives a reply to one of its command messages, it can use the RNG and SQN bytes to tie the reply message to its corresponding command. If the RNG and SQN bytes of a reply message match the RNG and SQN bytes of a command message, then that reply is the appropriate one for that command.

Whenever the command executor receives a command from another station, it should copy the RNG and SQN fields of the command message into the same fields of the corresponding reply message. Do not change the RNG and SQN values in a reply message. If you do, the command initiator will not be able to match its command to the corresponding reply message.

Note that the low byte (least significant bits) of your TNS value will be transmitted across the link before the high byte (most significant bits).

At any instant, the combination of SRC, CMD, RNG, and SQN are sufficient to uniquely identify every message packet in transit. At least 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 none of these fields is different, the command executor ignores the currently received message. This process is called duplicate message detection.

5-6

Chapter 5

Message Packet Formats

ADDR

The ADDR (address) field contains the address of a memory location in the command executor. ADDR specifies the address where the command is to begin executing. 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.

Note that the ADDR field specifies a byte address, not a word address as in PC programming. Chapter 6 explains how to convert PC word addresses to byte addresses.

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 station must return in its reply message. The allowed value for SIZE will vary with the type of command, as indicated in the command formats below.

Message Formats

DATA

The DATA field contains binary data from the application program. The number of data bytes in a message depends on the command or function being executed, as indicated in “Message Formats.” Chapter 6 gives some details on the format for the data field.

This section presents the detailed message formats for each type of command and reply message. PLC-5 processors cannot be interfaced directly with the Data Highway; they work only on Peer Communication Link (PCL) networks. To access a PLC-5 from a Data Highway station, join the two networks with a 1785-KA PLC-5/Data Highway adapter module. In this manual, the command message formats are discussed in the same order as Table 5.A:

5-7

Chapter 5

Message Packet Formats

If Y

ou W

ant This

Command:

T Message

Use This

CMD Code:

able 5.A

Formats

Use This

FNC Code:

If Y

ou W

Command:

ant This

Use This

CMD Code:

Use This

FNC Code:

Basic Command Set

Diagnostic Counters Reset Diagnostic Loop Diagnostic Read Diagnostic Status Protected Bit W Protected W Set ENQs Set NAKs Set T

imeout

Set V

ariables Unprotected Bit W Unprotected Read Unprotected W

Disable Outputs Enable Program Enable Scan Physical Read Physical W

Enter Download Mode Enter Upload Mode Exit Download/Upload Mode Physical Read Physical W Set Data Table Size

rite

PLC-2 Commands

rite

PLC-3 Commands PLC-5 Commands

06 06 06 06 02 00 06 06 06 06 05 01 08

PLC Commands

07 07 07 04 03

07 07 07 04 03 06

07 00 01

03 N/A N/A

02 N/A N/A N/A

03 N/A N/A

05 N/A N/A

PLC-4 Commands

Allocate Deallocate Initialize Processor Physical Read Physical W Physical Write with Mask Set to Program Mode Set to Run Mode Set to Single-Step Test Mode Set to Test Mode

rite

0E 0E 0E 0E 0E 0E 0E 0E 0E 0E

05 06 0C 0D 0E 0F 01 02 04 03

Bit W

rites Download Request File Read File W

rite Physical Read Physical W Restart Request Shutdown Request Upload Request W

ord Range Read

ord Range W

5-8

rite

0F 0F 0F 0F 0F 0F 0F 0F 0F 0F 0F

02 05 04 03 09 08 0A 07 06 01 00

Download All Request Download Completed Modify PLC-2 Compat. File Read Bytes Physical Read-Modify-Write Set Processor Mode T

yped Read

yped W Upload All Request Upload Completed W W W

rite

rite Bytes Physical ord Range Read ord Range W

rite

0F 0F 0F 0F 0F 0F 0F 0F 0F 0F 0F 0F 0F

Important: In the example formats that follow, CMD and FNC values are expressed in hexadecimal notation; all other values are in decimal form.

50 52 5E 17 26 3A 68 67 53 55 18 01 00

Chapter 5

Message Packet Formats

Basic Command Set

Basic commands include those that can generally be executed by any PC station on the communication link, regardless of the type of PC controller at that station. In some cases, switch settings on the station interface module can disable execution of a particular type of command at that station. For more details, refer to the user’s manual for the station interface module.

Basic commands are in two categories:

Privileged:

Computer

•

initiates. PCs execute.

Diagnostic Counters Reset Diagnostic Loop Diagnostic Read Diagnostic Status Set ENQs Set NAKs Set T

imeout

Set V

ariables

Non-Privileged:

PC stations and computer can initiate; only PCs can execute (unless the computer is programmed for execution).

•

Protected Bit W

•

Protected W

•

Unprotected Bit W

•

Unprotected Read

•

Unprotected W

rite

Diagnostic Counters Reset

This command resets to zero all the diagnostic timers and counters in the station interface module. The diagnostic status command gives the starting address for this block of counters and timers.

Command

Format:

SRCDST FNC

TNSSTSCMD

Reply Format:

SRCDST

TNSSTSCMD

5-9

Chapter 5

Message Packet Formats

Diagnostic Loop

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

Command

Reply Format:

Format:

SRCDST FNC

SRCDST

TNSSTSCMD

DATA

— Max. 243 Bytes

DATA

— Max. of 243 Bytes

Diagnostic Read

This command reads up to 244 bytes of data from the PROM or RAM of the station interface module. You can use it to read the module’s diagnostic timers and counters. Except for the PLC-5, you must use the diagnostic status command to obtain the starting address of the diagnostic counters. The PLC-5 doesn’t require that this address be specified, though you must include a dummy value in the ADDR field, which the PLC-5 will ignore.

5-10

Command

Reply Format:

Format:

SRCDST FNC

SRCDST

TNSSTSCMD

DATA

ADDR

— Max. of 244 Bytes

SIZE

Chapter 5

Message Packet Formats

Diagnostic Status

This command reads a block of status information from the station interface module. The reply to this command contains the status information in its DATA field.

Command

Reply Format:

Format:

SRCDST FNC

SRCDST DATA

TNSSTSCMD

— Max. of 244 Bytes

The status information varies with the type of station interface module. Table 5.B describes the contents of the status DATA field for 1771-KA, 1771-KC/KD, 1771-KE/KF, 1770-KF2, 1771-KG, 1774-KA, and 1785-KA modules. Table 5.C lists the status DATA for 1773-KA modules. Table 5.D describes this DATA for 1775-KA modules. Table 5.E describes this DATA for the PLC-5.

5-11

Chapter 5

Message Packet Formats

5-12

able 5.B

Contents

of Status DATA for 1771-KA2, -KC/KD, -KE/KF; 1770-KF2; 1771-KG, 1774-KA; and

1785-KA Modules

Byte Bit Value Meaning

1 Operating

3-4 Octal W

5-6

7-8

Status of PC Processor — For the 1770-KF2, this byte is always 0. For the 1785-KA, it has one of these values:

0 =

0-2 0

3 0

4 0

5 0

6, 7 T

ype of Station Interface Module and Processor

NOTE:

The 1770-KF2 identifies itself as a station interface module with a “3” in Byte 2, Bits 0 to 3 (i.e., as a 1771-KE/KF).

0-3 0

4-7 0

ord Address of the Start of PC Program — For the KF2 module, these are always 0. For the 1785-KA module, these are the

expansions of the interface module type bits and the processor type bits, respectively Memory Size (Number of Bytes) for PLC Processors; Zero Otherwise — For the 1785-KA module, this is the starting address of the counters on

the link other than the one from which the diagnostic read command was issued. Starting Byte Address of Diagnostic Counters and T

from which the diagnostic read command was issued. Series and Revision Level of Station Interface Module

NOTE:

The Series A 1770-KF2 identifies itself as Series “D” in Byte 9, Bits 5 to 7.; Series B KF2 identifies itself as Series E; and so on.

0-4 5-7

Settings of the Option Switches on the Station Interface Module — This byte is not used in replies by 1771-KC/KD or -KE/KF modules. For the other modules, the bits of this byte are defined as follows:

0-1 0

2 0

3 0

4 0

5 -- Not Used 6 0

7 0

Standby Mode

1 2 3 4 5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 1 0 1

1 2 3

Program Load Mode T

est Mode Run Mode (Not Used) Remote Program Load Remote T

Normal No Communication with PC

Normal Download Mode

Normal Format Error in Communication Zone of PC Program

Always Zero

1771-KC/KD Module 1771-KA Module 1774-KA Module 1771-KE/KF or 1770-KF2 Module 1771-KG Module 1771-KGM Module 1775-KA, Data Highway Port 1775-KA, RS-232-C Port 1773-KA, Data Highway Port 1773-KA, RS-232-C Port (Unused) PLC-5 Processor Interface (Unused) (Unused) Check Interface Module Expansion Byte (Byte 3) Computer

PLC Processor PLC-2 Processor PLC-2/20 (LP1) Processor Mini-PLC-2 Processor PLC-3 Processor PLC-2/20 (LP2) Processor PLC-2/15 Processor PLC-2/30 Processor PLC-4 Microtrol Processor (Not Used) (Not Used) PLC-5 Processor Interface (Not Used) (Not Used) Check Processor Expansion Byte (Byte 4) Computer

Revision A Revision B, etc. Series A Series B, etc.

57,600 Bits per Second Undefined Undefined Undefined

All Other PLC-2 Family Processors PLC-2 Processor

Protected Commands Enabled Protected Commands Disabled

Unprotected Commands Enabled Unprotected Commands Disabled

Physical Writes Enabled Physical Writes Disabled

ransmission Unprotected Commands Enabled

ransmission Unprotected Commands Disabled

1 =

On-Line Mode

est

. Both have a value of 16.

imers — For the 1785-KA module, this is the starting address of the counters on the link

1771-KA2 MODULE

Chapter 5

Message Packet Formats

Table

5.B Continued Contents of Status DATA for 1771-KA2, -KC/KD, -KE/KF; 1770-KF2; 1771-KG, 1774-KA; and 1785-KA Modules

Byte Bit Value Meaning

11 12

Cont’d

0 0

1 0

2 0

3 0

4 0

5-7 0

0 0

1 -- Not Used 2 0

3 0

4 0

5 0

6-7 0

0-1 0

2 -- Not Used 3-7

0 0

1 0

2-3 -- Not Used 4 -- Not Used 5 -- Not Used 6-7 -- Not Used Address of the PCL Active Node T (Low Byte First)

1 2 3 4 5 6 7

1 2 3

Half-Duplex Protocol Full-Duplex Protocol

Physical Writes Enabled Physical Writes Disabled

Unprotected Commands Enabled Unprotected Commands Disabled

Embedded Responses Enabled Embedded Responses Disabled

Even Parity No Parity

19,200 bps

Unprotected Commands Enabled Unprotected Commands Disabled

Physical Writes Enabled Physical Writes Disabled

ransmission of Unprotected Commands Enabled

ransmission of Unprotected Commands Disabled

Data Highway Port B Is Connected Data Highway Port A Is Connected

PLC Outputs Held in Last State PLC Outputs Turned Off

115,200 bps

57,600 Bits per Second Undefined Undefined undefined

Logical Complement of the State of Option Switch SW

57,600 Bits per Second Undefined

able

9,600 bps 4,800 bps 2,400 bps 1,200 bps

600 bps 300 bps 110 bps

57,600 bps 76,800 bps 38,400 bps

1771-KG MODULE

1774-KA MODULE

1770-KF2 MODULE

-1, Switches 1 through 5

1785-KA MODULE

Data Highway Baud Rate Switch

PCL Baud Rate Switch

5-13

Chapter 5

Message Packet Formats

able 5.C

Contents

of Status DATA for 1773-KA Modules

Byte Bit Value Meaning

1 Operating

3-4

5-6 RS-232-C Port Options

7-8 9

10 -- -- Not Used 11-114

Status of Controllers on the Loop

0 1 2 3 4 5 6 7

Station Interface T 0-3 8

4-7 8 Data Highway Port Options 0 0

1 -- Not Used 2 0

3 0

4 0

5-7 -- Not Used 8-15 --

0 0

1-3 0

4-10 -- Not Used 11 0

12 0

13 0

14 0

15 0

Starting Byte Address of Diagnostic Timers and Counters Module Series and Revision Level 0-4 0

5-7 0

Eight 13-byte groups of processor status data, one group for each of eight possible controllers on the loop. If a particular controller on the loop is not active or does not respond to the diagnostic status command, its 13 status bytes will be all zeros. Otherwise, each group of processor status bytes will contain the following:

1 1 1 1 1 1 1 1

ype

1 2 3 4 5 6 7

Byte 1

2 3 4 5 6 7 Error W 8 Error W 9

10 Pointer to END Statement (Low Byte)

11 12 13

If ” ” ” ” ” ” ”

1773-KA, Data Highway Port 1773-KA, RS-232-C Port

PLC-4 Microtrol Processor

57,600 Bits per Second Undefined

Privileged Commands Enabled Privileged Commands Disabled

Unprotected Commands Enabled Unprotected Commands Disabled

Protected Commands Enabled Protected Commands Disabled

Octal Station Number

Even Parity No Parity

Protected Commands Enabled Protected Commands Disabled

Embedded Responses Enabled Embedded Responses Disabled

Unprotected Commands Enabled Unprotected Commands Disabled

Privileged Commands Enabled Privileged Commands Disabled

Half-Duplex Protocol Full-Duplex Protocol

Revision A Revision B, Etc.

Series A Series B, Etc.

Program ID Processor ID Pointer to Start Program Pointer to End of A Size of I/O Processor Error Code

Processor Mode Pointer to END Statement (High Byte)

Pointer to End of Used Memory (Low Byte) Pointer to End of Used Memory (High Byte)

Controller 1 Controller 2 Controller 3 Controller 4 Controller 5 Controller 6 Controller 7 Controller 8

19,200 bps

8,600 bps 4,800 bps 2,400 bps 1,200 bps

ord Address (Low Byte) ord Address (High Byte)

600 bps 300 bps 110 bps

Is Active ” ” ” ” ” ” ”

vailable Memory

5-14

able 5.D

Contents

Byte Bit Value Meaning

of Status DATA for 1775-KA Modules

Chapter 5

Message Packet Formats

2 T

3 4

Operating Status of PLC-3 Processor 0-1 0

2 2 -3 0

1 4 0

1 5 0

1 6-7 --

ype of Station Interface

0-3 6

7 Current Context (Stored in Bits 4 to 7) Thumbwheel Number

Program Mode T

est Mode

Run Mode Not Used Normal

Major Processor Fault Normal

Shutdown Request Normal

Shutdown in Ef Not Used

1775-KA, Data Highway Port 1775-KA, RS-232-C Port

fect

5-6 7-8

10 11-14

15-18

Mode Control W Starting Byte Address of the Diagnostic Counters and T

block of diagnostic timers and counters for the Data Highway port and the RS-232-C port. The address given here is the one for the port that received the diagnostic status command.

Series and Revision Number of the 1775-KA Module 0-4 0

5-7 0

Not Used The Physical Address of the Unused W

physical address corresponding to the logical address E60.0.0.0. The Total Number of Words in the PLC-3 System Memory (Both Used and Unused) —

This is the physical word address that corresponds to the logical address E60.0.0.0.

ord — The logical address of the mode control word is E0.0.0.8.

imers — There is a separate

Revision A Revision B, Etc.

Series A Series B, Etc.

ord of PLC-3 System Memory — This is the

5-15

Chapter 5

Message Packet Formats

able 5.E

Contents of Status DATA for PLC-5

Byte Bit Value Meaning

1 Operating Status of PLC-5 Processor

0-2 0

3 0

4 0

5 -- Not Used 6 0

7 0

2 Processor Type

0-3 11 PLC-5 4-7 11 PLC-5

3-6 Size of User Memory (Low Word First, Low Byte First) 7 Series and Revision of PLC-5

0-4 0

5-7 0

8 Processor Number on PCL Link 9 I/O Address — Address of the processor if it is an adapter. If it is a scanner, then value is

0FDH.

10 I/O and Communication Parameters

0 1 2 5 6

11-12 Number of Data Table Files (Low Byte First) 13-14 Number of Program Type Files (Low Byte First) 15 Forcing Status

0 4

16 Memory Protect Indication — Non-Zero means memory is protected. 17 Bad RAM Indication — Non-Zero means RAM is bad, must be cleared.

Program Load Not Used Run Mode Not Used Remote Program Load Remote Test Remote Run Not Used

Normal Major Processor Fault

Normal Download Mode

Not Testing Edits Testing Edits

Revision A Revision B, Etc.

Series A Series B, Etc.

Double Density Adapter Mode Module Group 4 Top Half Adapter Is Half Rack PCL at 115K Baud

Forces Active Forces Are Present in the Tables

5-16

Chapter 5

Message Packet Formats

Protected Bit Write

This command sets or resets individual bits within limited areas of the PC data table memory. Its access is limited by memory access rungs in the communication zone of the PC’s ladder diagram program.

The data field in this packet consists of 4-byte blocks, each of which contains a 16-bit address field, a set mask, and a reset mask. Use the ADDR field to specify the address of the byte to be modified in the PC data table memory. Put the low byte (least significant bits) of the PC address value into the first byte of the ADDR field. Refer to Chapter 6 for more details on how to specify an address value.

Use the SET mask to specify which bits to set to 1 in the addressed PC byte. A 1 in a bit position of the SET mask means to set the corresponding bit in the addressed PC byte to 1; a 0 in a bit position of the SET mask means to leave the corresponding bit in the PC byte unchanged.

Use the RESET mask to specify which bits to reset to 0 in the addressed PC byte. A 1 in a bit position of the RESET mask means to reset the corresponding bit in the addressed PC byte to 0; a 0 in a bit position of the reset mask means to leave the corresponding bit in the PC byte unchanged.

Note that the interface module at the receiving PC station executes this command by first making a copy of the addressed PC byte. It then sets or resets the appropriate bits and writes the byte back into PC memory. At the same time, the PC processor can be changing the states of the original bits in memory. Because of this, some data bits may unintentionally be overwritten.

Command

Reply Format:

Format:

SRCDST

TNSSTSCMD

ADDR

SET ADDR SETRESET RESET Up to 60 Masks of

This Format

SRCDST

TNSSTSCMD

5-17

Chapter 5

Message Packet Formats

Protected Write

This command writes words of data into limited areas of the PC data table memory. Its access is limited by memory access rungs in the communication zone of the PC’s ladder diagram program.

Command

Reply Format:

Format:

SRCDST

TNSSTSCMD

ADDR DATA

— Max. of 243 Bytes

Set ENQS

This command sets the maximum number of ENQs that the station interface module will issue per message transmission. Put the number in the DATA field. The default setting for the KF2 module is 10 ENQs per transmission.

Command

Format:

5-18

SRCDST

Reply Format:

SRCDST

TNSSTSCMD

FNC 06

DATA

Chapter 5

Message Packet Formats

Set NAKS

This command sets the maximum number of NAKs that the station interface module will accept per message transmission. Put the number in the DATA field. The default setting for the KF2 module is 3 NAKs per transmission.

Command

Reply Format:

Format:

SRCDST

TNSSTSCMD

FNC 05

DATA

Set Timeout

This command sets the maximum amount of time that the station interface module will wait for an acknowledgment to its message transmission. The setting is expressed as the number of cycles of an internal clock, where 40 cycles equals 1 second. Put the number of desired cycles in the DATA field. The default setting for the KF2 module is 128 cycles, or about 3 seconds.

Command

Reply Format:

Format:

SRCDST

TNSSTSCMD

FNC 04

DATA

5-19

Chapter 5

Message Packet Formats

Set Variables

This command is a combination of the above three commands. It sets the maximum ENQs, NAKs, and timeouts all at once. Put the timeout setting in the first byte of the DATA field, the NAKs setting in the second byte, and the ENQs in the third byte.

Command

Reply Format:

Format:

SRCDST

TNSSTSCMD

FNC 02

DATA

Timeouts NAKs ENQs

— 3 Bytes

Unprotected Bit Write

This command sets or resets individual bits in any area of PC data table memory.

5-20

Use the RESET mask to specify which bits to reset to 0 in the addressed PC byte. A 1 in a bit position of the RESET mask means to reset the corresponding bit in the addressed PC byte to 0; a 0 in a bit position of the RESET mask means to leave the corresponding bit in the PC byte unchanged.

Chapter 5

Message Packet Formats

Command

Reply Format:

Format:

SRCDST

TNSSTSCMD

ADDR

Up to 60 Masks of

SET RESET

This Form

Unprotected Read

This command reads words of data from any area of PC data table memory. Use the SIZE field to specify the number of bytes to be read. To specify a number of PC words, SIZE should be an even value because PC words are two bytes long.

Command

Format:

SRCDST

Reply Format:

SRCDST

TNSSTSCMD

ADDR

DATA

SIZE

— Max. of 244 Bytes

5-21

Rockwell Automation 1770-KF2 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Data Highway or Data Highway Plus Asynchronous (RS-232-C or RS-422-A) Interface Module

Important User Information

Table of Contents

General

About This Manual

Module Description

Specifications

Data Highway Applications

PCL Applications

General

Physical Link Layer

Software Layers

General

Communication Option Switches

Mounting (Placing)

Installation

Diagnostic Indicators

General

Definition of Link Protocol

Full-Duplex Protocol

Half-Duplex Protocol

General

Application Layer

Network Layer

Message Packets

Message Formats