Rockwell Automation 1785-BCM, 1785-BEM, D17856.5.4 User Manual

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Allen-Bradley

PLC-5 Backup Communication

User

Module

(1785-BCM, 1785-BEM)

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Manual

Important User Information

Because of the variety of uses for this product and because of the differences between solid state products and electromechanical products, those responsible for applying and using this product must satisfy themselves as to the acceptability of each application and use of this product. For more information, refer to publication SGI-1.1 (Safety Guidelines For The Application, Installation and Maintenance of Solid State Control).

The illustrations, charts, and layout examples shown in this manual are intended solely to illustrate the text of this manual. Because of the many variables and requirements associated with any particular installation, Allen-Bradley Company cannot assume responsibility or liability for actual use based upon the illustrative uses and applications.

No patent liability is assumed by Allen-Bradley Company with respect to use of information, circuits, equipment or software described in this text.

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

Throughout this manual we make notes to alert you to possible injury to people or damage to equipment under specific circumstances.

ATTENTION: Identifies information about practices or circumstances that can lead to personal injury or death, property damage or economic loss.

Attention helps you:

- Identify a hazard

- Avoid the hazard

- recognize the consequences

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

Summary of Changes

This release of the publication contains new updated information.

To help you find updated information in this release of the manual, we have included change bars as shown to the left of this paragraph.

Using This Manual

Preface

Manual Objectives

Audience

This manual shows you how to use 1785-BCM series B backup communication modules with a PLC-5 programmable controller (PLC-5/15 series B, -5/20,

-5/25, -5/30, -5/40, and -5/60 processors). These modules enable high-speed communication transfer between two PLC-5 processors and provide system backup should the processor or other equipment in the system fail.

In this manual we describe:

backup system concepts procedures for installing and operating your modules various programming techniques

Before you read this manual or attempt to use 1785-BCM modules, you should be familiar with PLC-5 programmable controllers. In addition, you need to be familiar with:

6200 Series Software remote I/O system Data Highway Plus network block-transfer instructions

What this Manual Contains

an overview of backup concepts; description of backup system that uses 1785-BCM module.

a description of 1785-BCM module hardware. 2 – Understanding the 1785-BCM Module Hardware Components procedures for installing the1785-BCM module; procedures

for connecting the backup system. description of 1785-BEM backup expansion module and

procedures for installing an overview of how the 1785-BCM module and the backup

system operate; procedures for starting, powering-up, disconnecting, and restarting a repaired system.

considerations for timing, divergence, I/O forces, Data Highway Plus switching, Remote I/O switching, special sections of the data table, and data integrity.

The following table lists each chapter of this manual and describes the contents of each.

If you want to read about: Refer to chapter:

1 – Backup Concepts for the PLC-5 System

3 – Installing Your 1785-BCM Series B Backup System

4 – Installing Your 1785-BEM Module

5 – Operating Your PLC-5 Backup System

6 – Switchover Considerations

Preface

If you want to read about: Refer to chapter:

PLC-5

two methods you can use to program your backup system; considerations for using instructions that can cause problems in your backup system.

1785-BCM module faults (as indicated by the module’s status indicators and bits of the system status word) and procedures for correcting faults.

specifications for the 1785-BCM module. 9 – Specifications sample Programs for method 1 (transferring one block of

data at a time) and method 2 ( transferring multiple blocks of data at a time); data table transfer times for both programming methods.

answers to common PLC-5 backup system questions; delay times between the primary and the secondary processor for both programming methods and formulas for determining delay times.

describes differences between a 1785-BCM series A backup module and a 1785-BCM series B backup module

Processor Reference

7 – Programming Techniques

8 – Diagnosing Faults

Appendix A – Sample Programs

Appendix B – Reference Information

Appendix C – Using a Series A 1785-BCM Module

In this manual, the term PLC-5 processor refers to the following processors:

PLC-5/11 PLC-5/15 PLC-5/20 PLC-5/25 PLC-5/30 PLC-5/40 PLC-5/60 PLC-5/80

Terms and Conventions

Contact your Allen-Bradley Sales Office or your Allen-Bradley distributor for additional PLC-5 processors that can be configured with the 1785-BCM modules.

Some terms used in this manual may be unfamiliar to you. We list these terms with a brief definition of each.

HSSL is the 1785-BCM module’s High-Speed Serial Link. It is a dedicated

communication link between the primary and secondary 1785-BCM modules and is used to pass I/O, status, and data table information.

Primary System is the PLC-5 processor that controls the I/O and the other

equipment associated with that processor.

Secondary System is the PLC-5 processor that is ready to assume control of

the I/O and the equipment associated with that processor.

Backup System is the primary and secondary systems.

Preface

Switchover is the transfer of I/O control from the primary processor to the

secondary processor.

Bumpless switchover is the transfer of I/O control from the primary

processor to the secondary processor where the operation of the process being controlled is not affected.

Asynchronous processing is processing where the ladder program scan and

the block-transfer scan operate independently of each other within the same scan time.

BTW is block-transfer write; transfer of up to 64 words from the processor to

the block-transfer module.

BTR is block transfer read; transfer of up to 64 words from the block transfer

module to the processor.

Smart Switch Interface is a remote I/O interface in the 1785-BCM module

that responds to secondary scanner poll commands with actual input values from the remote I/O link, making the scanner think it is talking with remote I/O.

Related Publications

For more information about components used with the 1785-BCM module in a PLC-5 backup system, refer to the following publications:

Publication Title Publication Number

Enhanced and Ethernet PLC-5 Programmable Controllers User Manual

Classic 1785 PLC-5 Family Programmable Controllers Hardware Installation Manual

PLC-5 Programming Software Documentation Set 6200-N8.001

PLC-5 Programming Software: Installing and Configuring the Software

PLC-5 Programming Software: Programming 6200-6.4.7 PLC-5 Programming Software: Instruction Set Reference PLC-5 Programming Software: I/O Configuration Software

Remote I/O Adapter Module (cat. no. 1771-ASB) Installation Data 1771-2.162

1785-6.5.12

1785-6.6.1

6200-6.4.6

6200-6.4.11 6200-6.4.12

iii

Backup Concepts for the PLC-5 System

Understanding the 1785-BCM Hardware Components

Installing Your PLC-5 Backup System

Chapter 1

Chapter Objectives 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Why Use a Backup System? 1-1. . . . . . . . . . . . . . . . . . . . . . . . . . . .

Applying 1785-BCM Backup Communication Modules to

the PLC-5 Programmable Controller 1-2. . . . . . . . . . . . . . . . . . . . . .

What to do Next 1-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 2

Chapter Objectives 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Status Indicators 2-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Wiring Arm 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Communication Links 2-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Customer Relay 2-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Switch Assemblies 2-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I/O Backplane Interface 2-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

What to Do Next 2-7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 3

Chapter Objectives 3-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

PLC-5 Backup System Installation Overview 3-1. . . . . . . . . . . . . . .

Determining Power Supply Requirements 3-3. . . . . . . . . . . . . . . . .

Setting the I/O Chassis Switches 3-4. . . . . . . . . . . . . . . . . . . . . . . . .

Terminating the Data Highway Plus and Remote I/O Links 3-4. . . .

Installing the 1785-BCM Module 3-5. . . . . . . . . . . . . . . . . . . . . . . .

Connecting Your PLC-5 Backup System 3-9. . . . . . . . . . . . . . . . . .

What to Do Next 3-19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Installing Your 1785-BEM Module

Chapter 4

Chapter Objectives 4-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Backup Expansion Module 4-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Hardware Components 4-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Determining Power Supply Requirements 4-6. . . . . . . . . . . . . . . . .

Installing the 1785-BEM Module 4-7. . . . . . . . . . . . . . . . . . . . . . . .

Connecting Your 1785-BEM Module 4-13. . . . . . . . . . . . . . . . . . . . .

What to Do Next 4-21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents

Operating Your PLC-5 Backup System

Switchover Considerations

Chapter 5

Chapter Objectives 5-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

How the 1785-BCM Module Operates 5-1. . . . . . . . . . . . . . . . . . . .

How the Backup System Operates 5-13. . . . . . . . . . . . . . . . . . . . . . .

Starting the Backup System 5-17. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Powering Up the Backup System 5-18. . . . . . . . . . . . . . . . . . . . . . . .

Disconnecting/Repairing a Faulted Backup System 5-18. . . . . . . . . .

Restarting a Repaired Backup System 5-19. . . . . . . . . . . . . . . . . . . .

Switching the Processor’s Operating Mode 5-19. . . . . . . . . . . . . . . .

Editing or Programming On-line 5-20. . . . . . . . . . . . . . . . . . . . . . . . .

What to Do Next 5-20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chapter 6

Chapter Objectives 6-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Timing Requirements 6-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Divergence 6-3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Forcing I/O 6-4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Highway Plus Switching 6-4. . . . . . . . . . . . . . . . . . . . . . . . . . .

Remote I/O Switching 6-6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Table Considerations 6-9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Data Integrity 6-10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

What to Do Next 6-12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Programming Techniques

Diagnosing Faults

Specifications

Chapter 7

Chapter Objectives 7-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Getting Started 7-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Programming Methods to Transfer Data Table Values 7-3. . . . . . . .

Accounting for Instructions That Could Cause Problems

During Switchover 7-9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Summary of Programming Considerations 7-13. . . . . . . . . . . . . . . . .

Chapter 8

Chapter Objectives 8-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Diagnosing Faults with the Status Indicators 8-1. . . . . . . . . . . . . . .

Diagnosing Faults with Bits of the System Status Word 8-4. . . . . . .

Chapter 9

Specifications 9-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents

Sample Programs

Reference Information

Using a Series A 1785-BCM Module

Appendix A

Appendix

Method 1 Sample – Transferring Data One Block at a Time A-1. . . . . . . .

Method 2 Sample – Transferring Data Multiple Blocks at a Time A-13. . . .

Objectives

Appendix B

Appendix Answers to PLC-5 Backup Configuration Questions

Determining Data Table Transfer Time B-5. . . . . . . . . . . . . . . . . . . . . . . .

Objectives

Appendix C

Appendix 1785-BCM Series A Backup Module Characteristics

Objectives

A-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B-1. . . . . . . . . . . . . .

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

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

III

Chapter

Backup Concepts for the PLC-5 System

Chapter Objectives

Why Use a Backup System?

This chapter describes concepts for using a backup system with your programmable controller. In addition, this chapter provides an overview of a PLC-5 processor backup system that uses 1785-BCM backup communication modules and a system that also uses 1785-BEM backup expansion modules.

The objective of any redundant system (backup system) is to improve the amount of up-time of a machine or process by ensuring consistent availability of that machine, and by reducing costs associated with equipment failure. By using this backup system, you can guard your application against shutdowns caused by the programmable controller.

ATTENTION: Backup does not protect you from faults caused by programming errors or system timeouts because such an error or timeout will also occur in the secondary processor.

The backup option is used where you must transfer the control of the process to a secondary system, without thereby interrupting the machine/process operation.

To guard against system shutdown, a backup system must provide:

equipment with exceptional reliability automatic fault isolation minimal disturbance of the process when switching from the primary to

the secondary system

1-1

Chapter 1

Backup Concepts for the PLC-5 System

Applying 1785-BCM Backup Communication Modules to the PLC-5 Programmable Controller

A PLC-5 system configured with 1785-BCM modules provides high speed backup communication and switchover of the Data Highway Plus and remote I/O links. In this section we:

show a typical PLC-5 backup configuration explain how the backup system works describe the role of the 1785-BCM module (including 1785-BEM

module)

A Typical PLC-5 Backup Configuration

You must use BCM series B, revision C or later if you are using PLC-5/20,

-5/30, -5/40, or -5/60 processors.

A PLC-5 backup system contains two of each of the following hardware components:

PLC-5 processor module

Processor:

PLC-5/11 series A, revision B or later 1785-L11B PLC-5/15 series B, any revision 1785-LT series B PLC-5/20 series A, revision B or later 1785-L20B PLC-5/25 any revision 1785-LT2 PLC-5/30 series A, revision C or later 1785-L30B PLC-5/40 series A, revision F or later

PLC-5/60 series A, revision F or later

PLC-5/80 series C, revision A or later 1785-L80B

Contact your Allen-Bradley Sales Office or your Allen-Bradley distributor for additional PLC-5 processors that can be configured with the 1785-BCM modules.

or series B, revision C or later

Catalog Number:

1785-L40B

1785-L60B

1-2

1785-BCM module

1785-BEM module (when applicable)

power supply

local chassis

Figure 1.1 shows a typical PLC-5 backup configuration using PLC-5/15 processors and 1785-BCM modules. Figure 1.2 shows a typical PLC-5 backup configuration using PLC-5/40 or PLC-5/60 processors, 1785-BCM modules, and 1785-BEM modules.

Chapter 1

Backup Concepts for the PLC-5 System

Figure 1.1 PLC-5

Backup System Configuration Using 1785-BCM Module Only

Local I/O ChassisLocal I/O Chassis

1785 –BCM Module

PLC-5 processor PLC-5 processor

Remote I/O

1771 –P4S Power Supply

HSSL

Data Highway Plus

Remote I/O

Do not put modules for controlling your process in local I/O chassis.

Remote I/O Chassis Remote I/O Chassis

1785 –BCM Module

1771 –P4S Power Supply

To Data Highway Plus Network

1-4

Remote I/O

Applications that use more than two ports (PLC-5/40, or PLC-5/60 processors) may require a 1785-BEM module (not shown).

17990

Figure 1.2 PLC-5

Backup System Configuration Using 1785-BCM

and 1785-BEM Modules

Local I/O ChassisLocal I/O Chassis

Chapter 1

Backup Concepts for the PLC-5 System

1785 –BCM Module

PLC –5/60 or –5/40

1785 –BEM Module

1771 –P4S Power Supply

BCM DH+ or RIO

Remote I/O (BEM Module)

1785 –BCM Module

PLC –5/60 or –5/40

HSSL

BCM DH+ or RIO

BEM DH+ or RIO

BEM RIO

Remote I/O Chassis No. 1

1785 –BEM Module

1771 –P4S Power Supply

Do not put modules for controlling your process in local I/O chassis.

DH+ or RIO (BEM Module)

Remote I/O Chassis No. n

DH+ or RIO (BCM Module) DH+ or RIO (BCM Module)

HSSL connects between the two 1785-BCM modules only.

19088

1-5

Chapter 1

Backup Concepts for the PLC-5 System

How the PLC-5 Backup System Works

In the PLC-5 backup configuration, one system (consisting of one PLC-5 processor, 1785-BCM module, power supply, and chassis) controls the operation of the remote I/O. This system is referred to as the primary system. The other system is ready to take control of the remote I/O in the event of a fault in the primary system. This is referred to as the secondary system. The PLC-5 backup system does not back up local I/O; therefore, do not install I/O in the local chassis.

Data Transfer

During normal operation, the primary system sends remote input and data table data to the secondary system so that in the event of a switchover, the secondary system (which becomes the new primary system) has the same data.

Remote I/O data is automatically transferred over the High-Speed Serial Link (see Figure 1.1). This transfer is independent of the application program.

Data table values are transferred from the primary to the secondary system with block transfer instructions that you include in your ladder program. You do not have to transfer data table values if not necessary for your application. Figure 1.3 shows how data table data is transferred from the primary to the secondary system.

Figure 1.3 Transfer

Primary PLC-5

of Data T

BTW

able Data From the Primary to Secondary System

Primary 1785-BCM

Data is sent over the HSSL

Secondary 1785-BCM

BTR

Secondary PLC-5

11050I

For detailed information about data transfer from the primary to the secondary system, refer to Chapter 5, “Operating Your PLC-5 Backup System.”

1-6

Chapter 1

Backup Concepts for the PLC-5 System

Switchover

Should a fault occur in the primary processor, control switches to the secondary system in less than 50 ms (maximum). When a switchover occurs, the outputs in the remote I/O maintain their last state until they come under the control of the secondary processor.

However, keep in mind that the program scans of the two processors are not synchronized. This means that the secondary processor may be scanning all, none, or only part of the program (at your discretion). This manual explains the switchover process, and provides guidelines for developing programs for your PLC-5 backup system. (For more information about switchover, refer to Chapter 6, “Switchover Considerations.”)

Role of the 1785-BCM Series B Module

As an integral part of the backup system, the 1785-BCM modules enable high speed communication between the two PLC-5 processors, and permit the secondary processor to assume control of the process. In addition, the 1785-BCM module provides:

high speed transfer of the data table values from the primary to the

secondary system, to ensure that the secondary system’s data table is a copy of the primary system’s

a buffer of 4K words for data table values

exchange of information on the status of the primary and secondary

systems

automatic transfer to the secondary system of the remote input and

block transfer read values (analog values, etc.)

transfer of control from the primary processor to the secondary

processor when one of the following conditions occur:

- power failure

- processor fault

- 1785-BCM module fault

- change in the primary processor’s mode from: RUN to PROGRAM (manual switchover) REM RUN to REM PROG REM RUN to REM TEST

1-7

Chapter 1

Backup Concepts for the PLC-5 System

transfer of control from the primary processor to the secondary when

one of the following conditions is detected by the secondary processor:

- communication timeout in the High Speed Serial Link (HSSL)

between the two 1785-BCM modules and primary system is not updating the remote I/O

- transfer of control command from the primary 1785-BCM module

substitution of equipment without interruption of the process; that is, the

faulted system can be repaired while the other system is controlling the process

connections for remote I/O and Data Highway Plus network (the

1785-BCM module routes the remote I/O network and the Data Highway Plus network to the active processor)

isolation of the systems, in order to guarantee that a fault in one system

does not affect the other

What to do Next

diagnostics information

remote programming capability for secondary processor

capability of switching up to four configurable communication channels

when using the 1785-BEM backup expansion module

Backup Expansion

The 1785-BCM module has two channels. The PLC-5/40 and PLC-5/60 processors have four communication channels. You can provide the backup of the other two processor channels by adding the 1785-BEM backup expansion module. For more information about the 1785-BEM backup expansion module, refer to Chapter 4.

Compatibility

The 1785-BCM series B backup module is compatible with the 1785-BCM series A backup module when you properly configure switch assembly SW1 and switch assembly SW2 of the series B module.

This chapter provided an overview of backup concepts and the PLC-5 backup system. Read chapter 2 to understand the 1785-BCM module hardware components.

1-8

Chapter

Understanding the 1785-BCM Hardware Components

Chapter Objectives

Status Indicators

This chapter describes the major components that make up the 1785-BCM module. These components include:

status indicators 1771-WG wiring arm 1785-BCM communication links

- high-speed serial link (HSSL)

- Data Highway Plus link (DH+)

- remote I/O link (RIO)

customer relay (contact) switch assemblies backplane interface

Refer to Chapter 4 for information about the 1785-BEM backup expansion module.

The 1785-BCM module has five status indicators on the front panel of the module (Figure 2.1). The indicators show both normal operation and error conditions of your PLC-5 backup system.

Figure 2.1 1785-BCM

Module Status Indicators

Primary Secondary Backplane Serial Communication Link (HSSL) Fault

17978

2-1

Chapter 2

Understanding the 1785-BCM Hardware Components

All indicators light at power up or when a hardware fault occurs in the 1785-BCM module. With the exception of the FLT indicator, all of the 1785-BCM module’s indicators are related to individual bits of the system status word. For more information on the system status word, refer to Chapter 5, “Operating Your PLC-5 Backup System.”

For information about locating faults using the status indicators, refer to Chapter 8, “Diagnosing Faults”.

Wiring Arm

Communication Links

You make connections to your communication links with the 1771-WG wiring arm, which is shipped with the module.

Your wiring arm attaches to the pivot bar on the bottom of the I/O chassis. It pivots upward and connects with the module so you can install or remove the module without disconnecting the wires.

The 1785-BCM module has ports for three communication links for connection with the Remote I/O, Data Highway Plus network, and the other 1785-BCM module (Figure 2.2). In addition, the module has a relay for customer connection.

As shown in Figure 2.2, there are two user-configurable ports (Channels 1A and 1B) that support remote I/O or Data Highway Plus modes. Table 2.A lists the communication ports and describes how the system uses each one.

2-2

Figure 2.2 1785-BCM

Not Used

Module Communication Links

Chapter 2

Understanding the 1785-BCM Hardware Components

High Speed Serial Link

Not Used

Terminals 9, 10, and 11 are connected between the 1785–BCM modules in the backup system; in addition terminals 9, 10, and 11 of one of the 1785 BCM modules are connected to the DH+ network or to the remote I/O link.

Terminals 15, 16, and 17 are connected between the 1785–BCM modules in the backup system; in addition terminals 15, 16, and 17 of one of the 1785 BCM modules are connected to the DH+ network or to the remote I/O link.

2 1

Customer Relay

To Link

(RIO/DH+)

From Controller

To Link (RIO/DH+)

From Controller

Channel 1A (Remote I/O or Data Highway Plus)

Channel 1B (Remote I/O or Data Highway Plus)

19082

2-3

Chapter 2

Understanding the 1785-BCM Hardware Components

able 2.A

Communication

Communication Port: This link is used to:

High Speed Serial Link (HSSL) permit two-way alternating communication (half-duplex)

Channel 1A connect the primary PLC-5 processor to the Data Highway

Channel 1B connect the primary PLC-5 processor to the Data Highway

Ports

between the two 1785-BCM modules of the backup system at a distance of up to 15 feet.

Plus network or to the remote I/O link; the secondary processor is isolated from this link.

Channels 1A and 1B have a default communication mode which can be changed by resetting switches, if necessary. Table 2.B describes the default communication mode for each of the two channels.

able 2.B

Default

Communication Modes

Channel Default Communication Mode

1A Data Highway Plus 1B Remote I/O – Scanner mode at 57.6 kbaud

With the exception of the HSSL, all of the connections in the 1785-BCM module have an internal relay whose contacts are closed when the controller is primary and open when the processor is secondary. Figure 2.3 shows these relays for processor A and processor B of a PLC-5 backup system.

2-4

Figure 2.3 Relays

for Processor A and Processor B

Chapter 2

Understanding the 1785-BCM Hardware Components

Processor A (primary)

PLC-5

Customer Relay

Processor A (secondary)

PLC-5

Customer Relay

Processor B (secondary)

1785-BCM 1785-BCM

HSSL

DH+

Remote I/O

Processor B (primary)

1785-BCM 1785-BCM

HSSL

DH+

Remote

I/O

PLC-5

11051I

Customer Relay

Important: When using a 1785-BCM module with a PLC-5/40, PLC-5/60, or PLC-5/80 processor, you can add a 1785-BEM backup expansion module to provide backup for all processor communication channels. The channels of the 1785-BEM module, like the 1785-BCM module, can be configured for Data Highway Plus or remote I/O. For more information on the 1785-BEM backup expansion module, refer to Chapter 4.

The customer relay connection on the 1785-BCM module is used to switch external devices. Relay contacts are rated at .25A @ 24V dc resistive. Loads with inductive characteristics will require additional suppression devices.

2-5

Chapter 2

Understanding the 1785-BCM Hardware Components

Switch

Assemblies

There are two switch assemblies located at the top and at the bottom of the 1785-BCM module. Refer to Figure 2.4 for locations of the switch assemblies. Refer to Table 2.C for a description of the function of the 1785-BCM module switch assemblies.

Figure 2.4 1785-BCM

Module Switch Assemblies

Switch Assembly SW1

Top View

Switch Assembly SW2

Bottom View

19084

able 2.C

1785-BCM Module Switch Assembly Functions

Use this switch assembly: To:

SW1 • establish communication between the 1785-BCM

series B module and a 1785-BCM series A module.

• establish the fast data transfer mode from the secondary module to the secondary processor.

SW2 • specify if Channels 1A and 1B are going to establish

communication with Data Highway Plus network or with the remote I/O link. With the remote I/O link, determine the baud rate as well as the mode of operation of the processor (scanner or adapter).

To set the switches described above, refer to Chapter 5, “Operating Your PLC-5 Backup System.”

2-6

Chapter 2

Understanding the 1785-BCM Hardware Components

I/O Backplane Interface

What to Do Next

Through its connection with the I/O chassis backplane, the 1785-BCM module can execute block transfer read (BTR) and block transfer write (BTW) instructions from a PLC-5 processor. With the inherent block-transfer queuing capabilities of the PLC-5 processor, multiple block-transfer instructions per program scan can be executed to the same 1785-BCM module.

This chapter described the hardware components of the 1785-BCM module. Now that you are familiar with the module and some of the backup concepts for the PLC-5 backup system as described in chapter 1, you are ready to install the backup system. Chapters 3 and 4 describes installation procedures for the PLC-5 backup system (1785-BCM and 1785-BEM modules, respectively).

2-7

Chapter

Installing Your PLC-5 Backup System

Chapter Objectives

PLC-5 Backup System Installation Overview

This chapter provides an overview of an installed PLC-5 backup system and describes procedures for installing your PLC-5 backup system (1785-BCM series B module only). These procedures are:

determining power supply requirements setting the I/O chassis switches setting the module switches installing the 1785-BCM module connecting the PLC-5 backup system

When installing a backup system for a PLC-5/40, PLC-5/60, or PLC-5/80 processor, you may choose to use a 1785-BEM backup expansion module to provide backup for the two additional channels of the processor. Refer to Chapter 4 for installation procedures for the 1785-BEM backup expansion module.

Figure 3.1 shows a typical configuration of a PLC-5 backup system. In this system, communication between the controllers is accomplished through the two 1785-BCM modules. All of the cable connections between the primary and backup system require a 1770-CD (Belden 9463) cable.

Important: Do not install I/O modules for controlling your process in the local chassis. Only the I/O modules residing in the remote chassis will

be backed up. Local chassis are necessary for housing the processor, 1785-BCM backup communication module, 1785-BEM backup expansion module, and power supply for the backup system. Local I/O is not backed up.

When a coprocessor is in the same chassis (standalone mode) or directly connected to a PLC-5 processor (direct-connect mode), place the 1785-BCM and 1785-BEM modules in any other available I/O module group in that chassis

Important: Do not place the 1785-BCM module in the same module group (as defined by 2-slot addressing) as the coprocessor. The

1785-BCM module can reside in an adjacent slot, but not in the same module group (under the same chassis locking tab).

3-1

Chapter 3

Installing Your PLC-5 Backup System

Figure 3.1 PLC-5

Backup System Configuration

Local I/O ChassisLocal I/O Chassis

1785 –BCM Module

PLC-5 processor PLC-5 processor

Remote I/O

1771 –P4S Power Supply

HSSL

Data Highway Plus

Remote I/O

Do not put modules for controlling your process in local I/O chassis.

Remote I/O Chassis Remote I/O Chassis

1785 –BCM Module

1771 –P4S Power Supply

To Data Highway Plus Network

3-2

Remote I/O

Some applications that use more than two ports (PLC-5/40, PLC-5/60, or PLC-5/80 processors) may require a 1785-BEM module (not shown).

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Chapter 3

Installing Your PLC-5 Backup System

Determining Power Supply Requirements

The logic circuit of the 1785-BCM module is driven by a power supply through the backplane of the I/O chassis. Determine the power supply requirements for your PLC-5 backup system:

1. Add these values to determine output current needed from the power

supply.

1.0A at 5V for a 1785-BCM module and

2.5A for the PLC-5/15 or PLC-5/25 processor or

3.3A for PLC-5/11, -5/20, -5/30, -5/40, -5/60, or -5/80 processor

2. Refer to Table 3.A to choose the power supply that provides

sufficient power for all modules in your backup system.

Important: Refer to Chapter 4 to select your power supply when you add a 1785-BEM module in your backup system.

able 3.A

Power

Supplies for a PLC-5 Backup System

Power Supply Output Current (in amps) Power Supply Location

1771-P4 8 slot

1771-P4R

1771-P4S 8 slot

1771-P4S1 8 slot

1771-P6S 8 slot

1771-P6S1 8 slot

1771-P6R 8 slot

1771-PS7 16 external

A P4R redundant power supply can prevent system switchover due to power supply failures or incoming power failures.

You cannot use an external power supply and a power supply module to power the same chassis; they are not compatible.

1771-P5 8 slot

1771-P7 16 external

8 slot

2 2

3. Use separate power sources for the primary and secondary

processors. Connect the power supplies through different power sources to take precautions against interruptions and incoming power failures.

3-3

Chapter 3

Installing Your PLC-5 Backup System

Setting the I/O Chassis Switches

The I/O chassis switch assembly is located on the left side of the chassis backplane. Table 3.B lists the settings we recommend for the local chassis of your PLC-5 backup system. (Local refers to the chassis with the PLC-5 processor and the 1785-BCM module.) You can set remote system switches for your specific application. For more information about setting your I/O chassis backplane switches refer to the Enhanced and Ethernet PLC-5 Programmable Controllers User Manual (publication 1785-6.5.12).

Important: The addressing mode and local chassis size you select can affect the number of remote racks available. Refer to the Enhanced and Ethernet PLC-5 Programmable Controllers User Manual (publication 1785-6.5.12) for the maximum number of remote racks that can be addressed by the PLC-5 processor(s) in your system.

able 3.B

Recommended

Set switch(es) To this position:

2 and 3 both OFF – these switches are not used 4 and 5 4 – ON configure for 1/2-slot addressing*

6 and 7 as required for your application

Important:

switches 4 and 5 for 1/2-slot addressing or 1-slot addressing. If not configured as 1/2- or 1-slot addressing, a PLC-5 processor fault will occur

I/O Chassis Switch Settings for Local Chassis

1 OFF – to turn off outputs in the chassis when a fault is detected.

5 – OFF configure for 1/2-slot addressing*

8 as required for your application

The

1785-BCM module appears to the PLC-5 processor as a 32-point input module. Y

. If you are installing a 1785-BEM module, you must select 1/2-slot addressing.

ou must configure

Terminating the Data Highway Plus and Remote I/O Links

3-4

If your processor is an end device on the Data Highway Plus or remote I/O link, a terminator must be connected to the processor. In the PLC-5 backup system, you should set each PLC-5 processor in the backup system as if the other PLC-5 processor does not exist and no 1785-BCM modules are present. Terminate both links (DH+ and remote I/O):

for a PLC-5/15 or PLC-5/25 processor using switch assembly SW3 on

the PLC-5 processor. See Table 3.C.

for a PLC-5/11, -5/20, -5/30, -5/40, -5/60, or -5/80 processor by

installing an external resistor on the PLC-5 processor. See Table 3.D.

able 3.C

Terminate

Chapter 3

Installing Your PLC-5 Backup System

PLC-5/15 or -5/25 Backup System DH+ and Remote I/O Links

Installing the 1785-BCM Module

Set SW3

switch

1 ON – indicating that the PLC-5 processor is on the end of the remote I/O link 1 OFF – indicated that PLC-5 processor is not on the end of the remote I/O link 2 ON – indicating that PLC-5 processor is on the end of the DH+ link 2 OFF – indicating that PLC-5 processor is not on the end of the DH+ link

able 3.D Terminate and Remote I/O Links

For this kbaud: Install this terminating resistor:

57.6 or 115.2

230.4

Refer to the Enhanced and Ethernet PLC-5 Programmable Controllers User Manual to install the terminating resistor.

To this position:

PLC-5/1

1, -5/20, -5/30, -5/40, -5/60, or -5/80 Backup System DH+

150 ohm, 1/2 watt resistor 82 ohm

To install the 1785-BCM module, you:

key the I/O chassis

set the switches of the module

insert the module into the chassis

Electrostatic Discharge Damage

ATTENTION: Under some conditions, electrostatic discharge can degrade performance or damage the module. Observe the following precautions to guard against electrostatic damage.

Wear an approved grounded wrist strap or touch a grounded object to

discharge potential before handling the module.

Do not touch the backplane connector or connector pins.

you configure or replace internal components, do not touch other circuit

components

When not in use, keep the module in a static-shielded bag.

inside the module. If available, use a static-free work station.

3-5

Chapter 3

Installing Your PLC-5 Backup System

Keying Your I/O Chassis

Use the plastic keying bands, shipped with each I/O chassis, to key the chassis slot to accept only the 1785-BCM module.

The module circuit board is slotted in two places on the rear edge. The position of the keying bands on the backplane connector must correspond to these slots to allow insertion of the module. You can key any connector in an I/O chassis to receive this module except for the left-most connector reserved for the processor modules.

Place keying bands between the following numbers labeled on the backplane connector (Figure 3.2):

Between 8 and 10

Between 34 and 36

Figure 3.2 Keying

Positions

Backplane Connectors

11052I

Keying bands

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36

Setting the 1785-BCM Series B Switch Assemblies

The switch assembly SW1, located at the top of the 1785-BCM module, has four switches as shown in Figure 3.3. Refer to Table 3.E for instructions on setting the four switches. The functions of the four switches are:

Switch 1 indicates to the 1785-BCM series B module whether the other

1785-BCM module is a series A or a series B module. If it is a series A module, functions of switches 2 through 4 will not apply.

3-6

Switch 2 selects the Fast Data-Transfer mode from the secondary

module to the secondary processor (1785-BCM series B module only).

Switch 3 is not used.

Switch 4 is not used.

Chapter 3

Installing Your PLC-5 Backup System

The 1785-BCM series B module switch assembly SW1 is preset at the factory to operate:

with another 1785-BCM series B module

in the Fast Data-Transfer mode. Fast data-transfer mode means that

when the secondary module receives a data block, it immediately enables it to be read by the secondary processor.

Figure 3.3 1785-BCM

Series B Switch Assembly SW1

Switch Assembly SW1

Toggle pushed toward top OFF (open).

Top View

able 3.E Setting 1785-BCM Series B SW1 Switches

When: Set this switch: To this position:

the other 1785-BCM module is a series A 1

ON (closed) OFF (opened) OFF (opened) OFF (opened) OFF (opened) ON (closed) ON (closed) OFF (opened) ON (closed)

Toggle pushed toward bottom ON (closed).

19085

OFF (opened) the other 1785-BCM module is a series B 1 OFF (opened) you want fast data transfer 2 you want the secondary BCM module to enable

BTRs to the secondary PLC-5 processor only when all blocks of a multi-block segment have been received

ON (closed)

OFF (opened)

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Chapter 3

Installing Your PLC-5 Backup System

When: To this position:Set this switch:

switch 3 is always unused 3 OFF (opened) switch 4 is always unused 4 OFF (opened)

To be compatible with 1785-BCM series A modules, you must set these switches as

shown. If you use this module with a series A module and do not set switch assembly SW2 as shown, the LEDs on the series B module will flash.

This switch applies when both modules are 1785-BCM series B modules only.

The switch assembly SW2, located at the bottom of the 1785-BCM series B module, has six switches. The function of the six switches is to establish the configuration of Channels 1A and 1B of the module. Refer to Figure 3.4 for the location of SW2.

Figure 3.4 1785-BCM

Series B Switch Assembly SW2

Switch Assembly SW2

Toggle pushed toward top OFF (open).

Toggle pushed toward bottom

Bottom View

ON (closed).

Switches 1, 2, and 3 determine the configuration of Channel 1A. Switches 4, 5, and 6 determine the configuration of Channel 1B. These channels can be configured for Data Highway Plus or Remote I/O mode, either with the PLC-5 processor operating in adapter mode or in scanner mode.

The 1785-BCM series B module is shipped with Channel 1A configured for Data Highway Plus and Channel 1B configured for Remote I/O ( to be used with a processor in scanner mode set at 57.6 kbaud).

Refer to Table 3.F to configure Channels 1A and 1B using switch assembly SW2 switches.

19086

3-8

able 3.F

Configuring

Chapter 3

Installing Your PLC-5 Backup System

1785-BCM Series B Channels 1A and 1B using SW2

Configure Channel 1A switches Configure Channel 1B switches

for:

Data Highway Plus network at 57.6 kbaud (refer to Chapter 5, section “Secondary Processor Remote Programming”)

Remote I/O – adapter mode using 57.6 kbaud ON ON OFF Remote I/O – adapter mode using 115.2 kbaud ON OFF ON Remote I/O – adapter mode using 230.4 kbaud ON OFF OFF Relay switching or unused Channel Remote I/O – scanner mode with 57.6 kbaud OFF ON OFF Remote I/O – scanner mode with 115.2 kbaud OFF OFF ON Remote I/O – scanner mode with 230.4 kbaud OFF OFF OFF

Switches 1, 2, and 3 determine configuration for Channel 1A.

Switches 4, 5, and 6 determine configuration for Channel 1B.

Does not function as a smart switch but as a relay with contacts either opened or closed. Also, set

the switches in this configuration if you are not going to use this channel.

1 2

1 4

ON ON ON

OFF ON ON

2 5

3 6

Important: The positions of the switches are read at the module power-up. If the position of the switches is changed after module power-up, the 1785-BCM module does not recognize the new position.

Inserting the 1785-BCM Module into the I/O Chassis

To insert the 1785-BCM module in your I/O chassis, perform the following steps. We recommend that you insert your 1785-BCM module into the left-most slot of the first I/O module group in the I/O chassis.

ATTENTION: Remove power from the 1771 I/O chassis backplane and wiring arm before removing or installing an I/O module.

Failure to remove power from the backplane or wiring arm could cause module damage, degradation of performance, or injury.

Failure or equipment damage due to possible unexpected operation.

to remove power from the backplane

could cause injury

3-9

Chapter 3

Installing Your PLC-5 Backup System

1. Turn off power to the I/O chassis.

2. Place the module in the plastic tracks on the top and bottom of the

slot that guides the module into position.

3. Do not force the module into its backplane connector. Apply firm,

even pressure on the module to seat it properly.

4. Snap the chassis latch over the top of the module to secure its

position.

5. Connect the wiring arm to the module.

6. Make wiring connections to the wiring arm as indicated in the next

sections.

Connecting Your PLC-5 Backup System

To connect your PLC-5 backup system, you:

connect the 1785-BCM modules make remote I/O connections make Data Highway Plus network connections

You make the connections to the 1785-BCM module’s wiring arm (cat. no. 1771-WG). Figure 3.5 shows an overview of the connections.

Important: Note that the connections described in the following paragraphs refer to the 1785-BCM module default configuration, that is Channel 1A is configured for Data Highway Plus and Channel 1B is configured for Remote I/O scanner mode.

3-10

Figure 3.5

assis B

1785-BCM

Chapter 3

Installing Your PLC-5 Backup System

Module Connections

Ch 1A

RIO/DH+

Ch 1B

DH+/RIO

Clear

Shield

Blue

Clear

Shield

Blue

Clear

Shield

Blue

Shield

Clear

Chassis A

Blue

Shield

Clear

Shield

Blue

Shield

Clear

HSSL

Ch 1A

Ch 1B

Clear

Shield

Blue

Shield

Clear

Shield

Blue

Clear

Shield

Blue

Shield

Clear

Shield

Blue

Replace this with a terminator if this node is at the end of this physical link.

Blue

Shield

Clear

PLC-5/40

Blue

Shield

Clear

Blue

Shield

Clear

1785-BCM Series B

PLC-5/40

Blue

Shield

Clear

Blue

Shield

Clear

1785-BCM Series B

3-11

Chapter 3

Installing Your PLC-5 Backup System

Local I/O Chassis Local I/O Chassis

Connecting the 1785-BCM Modules

Connect the High Speed Serial Link (HSSL) to establish communication between the 1785-BCM modules of the primary system and the secondary system. The cable for these connections can be a maximum of 15 feet. To do this, connect a 1770-CD or Belden 9463 cable to terminals 1, 2, and 3 on the wiring arm of each 1785-BCM module as shown in Figure 3.6.

Figure 3.6 1785-BCM

Module Connections for High-Speed Serial Link

1785-BCM module

PLC-5 processor PLC-5 processor

1771-P4S power supply

High Speed Serial Link (HSSL)

1770-CD Cable or Belden 9463 (15 feet maximum)

Blue Shield

Clear

1785-BCM module

1771-P4S power supply

Blue Shield

Clear

Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O Scanner.

ATTENTION: The 1785-BCM series B module communicates with the 1785-BCM series A module only if switch 1 of the SW1 switch assembly is set to ON and if SW2 switch assembly is properly configured.

3-12

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Chapter 3

Installing Your PLC-5 Backup System

Making Remote I/O Connections

Figure 3.7 shows Channel 1B configured to establish communication with the remote I/O scanner mode (default configuration). The connections you must make for your PLC-5 backup system are between the:

PLC-5 and the 1785-BCM module two 1785-BCM modules 1785-BCM module and Remote I/O Adapter module

Steps to make these connections follow the figure.

Figure 3.7 Remote

I/O Connections

Local I/O ChassisLocal I/O Chassis

1785 –BCM Module

PLC-5 processor PLC-5 processor

Remote I/O

1771 –P4S Power Supply

Remote I/O

Remote I/O Chassis No. 1 Remote I/O Chassis No. n

1785 –BCM Module

1771 –P4S Power Supply

Remote I/O

Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O Scanner.

HSSL was previously connected but is not shown for clarity. Make all connections with 1770-CD cable.

17981

3-13

Chapter 3

Local I/

assis Local I/

assis

Installing Your PLC-5 Backup System

1. Connect one end of a 1770-CD cable to the REM I/O connector on

one of the PLC-5 programmable controllers as shown in Figure 3.8.

Figure 3.8 Remote

I/O Connections Added Between PLC-5 and 1785-BCM Module

PLC-5 processor

O Ch

1785-BCM module

1771-P4S power supply

Remote I/O

PLC-5 processor

O Ch

1785-BCM module

1771-P4S power supply

Remote I/O

Blue

Shield

Clear

Blue

Shield

Clear

HSSL was previously connected but is not shown for clarity. Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O scanner.

2. Connect the other end of the 1770-CD cable to terminals 18, 19, and 20 on the wiring arm of the 1785-BCM module in the same chassis as

shown in Figure 3.8.

3-14

17982

Chapter 3

Local I/

assis

Local I/

assis

Installing Your PLC-5 Backup System

3. Perform steps 1 and 2 for the other PLC-5 programmable controller and 1785-BCM module.

4. Connect a 1770-CD cable to terminals 15, 16, and 17 on each of the 1785-BCM wiring arms as shown in Figure 3.9.

Figure 3.9 Remote

I/O Connections Added Between 1785-BCM Modules

O Ch

1785-BCM Moddule

PLC-5 processor PLC-5 processor

Blue

Shield

1771-P4S power supply

O Ch

1785-BCM Moddule

1771-P4S power supply

Blue

Clear

HSSL was previously connected but is not shown for clarity. Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O scanner.

5. Connect one end of a 1770-CD cable to terminals 15, 16, and 17 on the wiring arm of one of the 1785-BCM modules as shown in Figure 3.10.

Shield

Clear

17983

3-15

Chapter 3

Installing Your PLC-5 Backup System

Figure 3.10 Remote

I/O Connections Added Between 1785-BCM Module

and Remote I/O Adapter Module

Local I/O ChassisLocal I/O Chassis

1785-BCM Module

PLC-5 processor PLC-5 processor

1771-ASB Remote Adapter Module

15 16 17

1771-P4S power supply

Blue Shield

Clear

Remote I/O Chassis No. 1

1785-BCM Module

1771-P4S power supply

1771-ASB Remote Adapter Module

Remote I/O Chassis No. n

3-16

Blue

Shield

Clear

HSSL was previously connected but is not shown for clarity.

1 2 3

Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O Scanner.

Note that the remote I/O link from the adapters connect to either 1785-BCM module; the remote I/O link does not connect directly to the processor.

17984

Chapter 3

Local I/

assisLocal I/

assis

Installing Your PLC-5 Backup System

6. Connect the other end of the 1770-CD cable to terminals 1, 2, and 3

on the wiring arm of the Re

mote I/O Adaptor module as shown in

Figure 3.10.

Making Data Highway Plus Connections

Figure 3.11 shows Channel 1A configured to establish communication with Data Highway Plus network (default configuration). The connections you must make for your PLC-5 backup system are between the:

PLC-5 and the 1785-BCM module two 1785-BCM modules 1785-BCM module and Data Highway Plus network

Steps to make these connections follow the figure.

Figure 3.1 Data

OCh

1785-BCM Module

PLC-5 processor PLC-5 processor

HSSL and Remote I/O link were previously connected but are not shown for clarity.

Highway Plus Connections

1771-P4S Power Supply

Data Highway Plus

Data Highway Plus Network

OCh

1785-BCM Module

1771-P4S Power Supply

Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O Scanner.

Make all connections with 1770-CD cable.

17986

3-17

Chapter 3

Local I/

assisLocal I/

assis

Installing Your PLC-5 Backup System

1. Connect one end of a 1770-CD cable to the PEER COMM INTFC connector on one of the PLC-5 programmable controllers, as shown in Figure 3.12.

Figure 3.12 Data

Highway Plus Connections Added Between PLC-5

and 1785-BCM Module

OCh

1785-BCM Module

PLC-5 processor PLC-5 processor

Data Highway Plus

1771-P4S Power Supply

Data Highway Plus

OCh

1785-BCM Module

1771-P4S Power Supply

3-18

Clear Shield

Blue

Clear

Shield

Blue

HSSL and Remote I/O link were previously connected but are not shown for clarity.

Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O Scanner.

17985

Chapter 3

Installing Your PLC-5 Backup System

2. Connect the other end of the 1770-CD cable to terminals 12, 13, and 14 on the wiring arm of the 1785-BCM module in the same chassis as

shown in Figure 3.12.

3. Perform steps 1 and 2 for the other PLC-5 programmable controller and 1785-BCM module.

4. Connect a 1770-CD cable to terminals 9, 10, and 11 on the wiring arm of each 1785-BCM module as shown in Figure 3.13.

Figure 3.13 Data

Highway Plus Connections Added Between 1785-BCM Modules

Local I/O Ch assisLocal I/O Cha ssis

1785-BCM Module

PLC-5 processor PLC-5 processor

1771-P4S Power Supply

Data Highway Plus

Clear

1785-BCM Module

1771-P4S Power Supply

Clear

10 11

Shield

Blue

HSSL and Remote I/O link were previously connected but are not shown for clarity.

Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O Scanner.

10 11

Shield

Blue

17987

3-19

Chapter 3

Local I/

assisLocal I/

assis

Installing Your PLC-5 Backup System

5. Connect the 1770-CD cable from the Data Highway Plus network to 9, 10, and 11 on the wiring arm of one of the 1785-BCM modules as

shown in Figure 3.14.

Figure 3.14 Data

Highway Plus Connections Added Between 1785-BCM Module and

Data Highway Plus Network

OCh

1785-BCM Module

PLC-5 processor PLC-5 processor

1771-P4S Power Supply

Clear S h ield

Blue

Data Highway Plus

Data Highway Plus Network

HSSL and Remote I/O link were previously connected but are not shown for clarity.

Connections show default configuration with Channel 1A as Data Highway Plus and Channel 1B as Remote I/O Scanner.

OCh

1785-BCM Module

1771-P4S Power Supply

What to Do Next

3-20

Note that the Data Highway Plus connects to either 1785-BCM module; it does not connect directly to the processor.

Now that you’ve installed your PLC-5 backup system and made connections, you are ready to start up your system. Before doing so, double check all connections against the procedures described in this chapter. If your backup systems requires the use of a 1785-BEM module, refer to Chapter 4 for a description of the module and installation procedures. Chapter 5 describes the operation of the 1785-BCM module and the backup system and shows procedures for starting up and operating your system.

Chapter

Installing Your 1785-BEM Module

Chapter Objectives

Backup Expansion Module

Hardware Components

This chapter:

describes the 1785-BEM backup expansion module identifies major components of the 1785-BEM module provides an overview of an installed PLC-5/40, -5/60, or -5/80

backup system provides procedures for determining power supply requirements provides procedures for installing your 1785-BEM modules provides procedures for connecting the 1785-BEM modules in the

PLC-5 backup system

The 1785-BEM is the backup expansion module for the 1785-BCM series B module. It has the capability of switching two additional configurable communication channels when you are using a 1785-BCM series B module with a PLC-5/40, -5/60, or PLC-5/80 processor.

The major components of a 1785-BEM module are:

status indicators 1771-WG wiring arm 1785-BEM communication links

- Data Highway Plus (DH+)

- remote I/O (RIO) customer relay (contact) switch assembly I/O backplane interface

4-1

Chapter 4

Installing Your 1785-BEM Module

Status Indicators

The 1785-BEM module has two status indicators on the front panel of the module (Figure 4.1).

Figure 4.1 1785-BEM

Module Status Indicators

BACKUP

EXPANSION

Run Fault

19087

RUN (green) indicator is on to show normal operation of the 1785-BEM module.

FLT (red) indicator is on when a hardware fault is detected in the 1785-BEM module.

Note that these indicators light at power up or when a hardware fault occurs in the 1785-BEM module.

ATTENTION: If the RUN indicator is blinking on the secondary 1785-BEM module, it means that there is a switch setting error. Note that switches of switch assembly SW2 must be in the same position in both 1785-BEM modules. (If the blinking RUN indicator goes unnoticed, it could prevent a switchover.)

4-2

Chapter 4

Installing Your 1785-BEM Module

Wiring Arm

You make connections to your communication links with the 1771-WG wiring arm, which is shipped with the module.

Your wiring arm attaches to the pivot bar on the bottom of the I/O chassis. It pivots upward and connects with the module so that you can install or remove the module without disconnecting the wires.

Communication Links

The 1785-BEM module has ports for two communication links that connect with remote I/O and Data Highway Plus network (Figure 4.2). In addition, the module has a relay for customer connection.

Figure 4.2 1785-BEM

Module Communication Links

Not Used

Customer Relay

Not Used

To Link (RIO/DH+)

From Controller

To Link (RIO/DH+)

From Controller

Not Used

Terminals 9, 10, and 11 are connected between the 1785 –BEM modules in the backup system; in addition terminals 9,

10, and 11 of one of the 1785 –BEM modules are connected to the DH+ network or to the Remote I/O link.

Terminal 15, 16, and 17 are connected between the 1785 –BEM modules in the backup system; in addition, terminals

15, 16 and 17 of one of the 1785 –BEM modules are connected to the DH+ network or to the Remote I/O link.

Channel A (Remote I/O or Data Highway Plus)

Channel B (Remote I/O or Data Highway Plus)

19083

4-3

Chapter 4

Installing Your 1785-BEM Module

As shown in Figure 4.2, there are two user-configurable ports (Channels 2A and 2B) that support remote I/O or Data Highway Plus modes.

Table 4.A lists the communication ports and describes how the system uses each port.

able 4.A

Communication

Communication Port This link is used to:

Channel 2A connect the primary PLC-5/40, -5/60, or PLC-5/80 processor to the Data

Channel 2B connect the primary PLC-5/40, -5/60, or PLC-5/80 processor to the Data

Ports

Highway Plus network or to the Remote I/O link; the secondary PLC-5/40 or PLC-5/60 processor is isolated from this link.

The 1785-BEM module is shipped with Channel 2A configured for Data Highway Plus mode and Channel 2B configured for Remote I/O scanner mode at 57.6 kbaud (default configuration).

Important: Note that I/O, status, and data table communication between the primary and secondary backup systems is accomplished over the HSSL, which is connected between the primary and secondary 1785-BCM modules only. Each 1785-BEM module communicates with the 1785-BCM series B module, in its same rack, via a secondary backplane bus. Remote I/O or Data Highway Plus is connected between the primary and secondary 1785-BEM modules through Channels 2A and 2B.

Channels 2A or 2B have an internal relay whose contacts are closed when the controller is primary and are open when the processor is secondary. Figure 4.3 shows these relays for processor A and processor B of a PLC-5 backup system.

4-4

Figure 4.3 Relays

for Processor A and Processor B

Chapter 4

Installing Your 1785-BEM Module

Processor A (primary)

1785-BCM

PLC-5

2A 2B

1A 1B

Processor A (secondary)

1785-BCM

PLC-5

2A 2B

1A 1B

Processor B (secondary)

1785-BEM 1785-BEM

DH+/RIO

Processor B (primary)

1785-BEM 1785-BEM

1785-BCM

PLC-5

2A 2B

1A 1B

1785-BCM

PLC-5

2A 2B

1A 1B

DH+/RIO

11679I

Customer Relay

The customer relay connection on the 1785-BEM module is used to switch external devices. Relay contacts are rated at .25A at 24V DC resistive. Loads with inductive characteristics will require additional suppression devices.

4-5

Chapter 4

Installing Your 1785-BEM Module

Switch Assembly

The 1785-BEM module has a switch assembly which specifies if Channels 2A and 2B are going to establish communication with Data Highway Plus network or with the remote I/O link. When the module establishes communication with the remote I/O link, the switch also determines the baud rate and the mode of operation of the processor (scanner or adapter). To set these switches, refer to the section on “Setting the Switch Assembly.”

I/O Backplane Interface

The 1785-BEM module communicates with the 1785-BCM module through its connection with the I/O chassis backplane.

Determining Power Supply Requirements

The logic circuit of the 1785-BEM module is driven by the power supply through the backplane of the I/O chassis. Use the following guidelines to determine the power supply requirements for your PLC-5 backup system.

1. Add these values to determine output current needed from the power

supply for all the modules in that chassis.

0.6A at 5V for the 1785-BEM module and

1.0A at 5V for the 1785-BCM module and

3.3A for the PLC-5/40 or PLC-5/60 processor

2. Refer to table 3.A, Power Supplies for a PLC-5 Backup System, to

select your power supply.

3. Use separate power sources for the primary and secondary

processors. Connect the power supplies through different power sources to take precautions against interruptions and incoming power failures.

4-6

Chapter 4

Installing Your 1785-BEM Module

Installing Module

the 1785-BEM

The installation procedures for the 1785-BEM backup expansion module are:

determining power supply requirements setting the 1785-BEM module switches keying the I/O chassis inserting the module into the chassis

ATTENTION: In the backup system, switch 1 of the local I/O chassis should be in OFF position in order to allow the switchover when a fault is detected. In remote chassis, this switch should be positioned at the user’s discretion.

Figure 4.4 shows a typical configuration of a PLC-5 backup system using the 1785-BEM module. In this system, all of the cable connections between the primary and backup system require a 1770-CD cable.

Important: Do not install I/O modules for controlling your process in the local chassis. Only the I/O modules residing in the remote chassis will

be backed up. Local chassis are necessary for housing the processor, 1785-BEM module, 1785-BCM module, and power supply for the backup system.

4-7

Chapter 4

Installing Your 1785-BEM Module

Figure 4.4 PLC-5

Backup System Configuration (using a 1785-BEM module)

1785-BCM module 1785-BEM module1785-BCM module 1785-BEM module

PLC-5/40 or -5/60 PLC-5/40 or -5/60

1771-P4S Power Supply

Local I/O ChassisLocal I/O Chassis

1771-P4S Power Supply

Remote I/O

(BEM module)

HSSL

BCM DH+ or RIO

BEM DH+ or RIO

BEM RIO

BCM DH+ or RIO

Remote I/O Chassis No. 1

Do not put modules for controlling your process in local I/O chassis.

DH+ or RIO (BEM module)

Remote I/O Chassis No. n

4-8

HSSL connects between the two 1785-BCM modules only.

DH+ or RIO (BCM module)

19088

Chapter 4

Installing Your 1785-BEM Module

Electrostatic Discharge Damage

ATTENTION: Under some conditions, electrostatic discharge can degrade performance or damage the module. Observe the following precautions to guard against electrostatic damage.

Wear an approved grounded wrist strap or touch a grounded object to

discharge potential before handling the module.

Do not touch the backplane connector or connector pins.

If you configure or replace internal components, do not touch other

circuit components inside the module. If available, use a static-free work station.

When not in use, keep the module in a static-shielded bag.

Keying the I/O Chassis

Use the plastic keying bands, shipped with each I/O chassis, to key the chassis slot to accept only the 1785-BEM module.

Figure 4.5 Keying

Positions

2 4 6 8 10 12 14

Keying bands

16 18 20 22 24 26 28 30 32 34 36

11680I

4-9

Chapter 4

Installing Your 1785-BEM Module

Setting the 1785-BEM Module Switch Assembly

Switch assembly SW2, located at the bottom of the 1785-BEM module, has six switches. The function of the six switches is to establish the configuration of Channels 2A and 2B of the module. Figure 4.6 shows the location of SW2.

Figure 4.6 Switch

Assembly SW2

Switch Assembly SW2

Toggle pushed toward top OFF (open).

Toggle pushed toward bottom

Bottom View

ON (closed).

Switches 1, 2, and 3 determine the configuration of Channel 2A. Switches 4, 5, and 6 determine the configuration of Channel 2B.

These channels can be configured for Data Highway Plus (DH+) or for Remote I/O (RIO) mode with the PLC-5 processor operating either in adapter mode or in scanner mode.

The 1785-BEM module is shipped with Channel 2A configured for Data Highway Plus (DH+) and Channel 2B configured for Remote I/O (RIO) with the processor in scanner mode at 57.6 kbaud.

Refer to Table 4.B to configure Channels 2A and 2B using switch assembly SW2 switches.

19086

4-10

able 4.B

Configuring

Chapter 4

Installing Your 1785-BEM Module

Channels 2A and 2B

Configure Channel 2A switches Configure Channel 2B switches

for:

Data Highway Plus network ON ON ON Remote I/O – adapter mode using 57.6 kbaud ON ON OFF Remote I/O – adapter mode using 115.2 kbaud ON OFF ON Remote I/O – adapter mode using 230.4 kbaud ON OFF OFF Relay switching or unused Channel Remote I/O – scanner mode with 57.6 kbaud OFF ON OFF Remote I/O – scanner mode with 115.2 kbaud OFF OFF ON Remote I/O – scanner mode with 230.4 kbaud OFF OFF OFF

Switches 1, 2, and 3 determine configuration for Channel 2A.

Switches 4, 5, and 6 determine configuration for Channel 2B.

Does not function as a smart switch but as a relay with contacts either opened or closed. Also, set

the switches in this configuration if you are not going to use this channel.

1 2

OFF ON ON

2 5

3 6

Important: The positions of the switches are read at module power-up. If the position of the switches is changed after module power-up, the 1785-BEM module will not recognize the new position.

Inserting the 1785-BEM Module into the I/O Chassis

To insert the 1785-BEM module in your I/O chassis, perform the following steps. We recommend that you insert you 1785-BEM module into the right-most slot of the first I/O module group in the I/O chassis. The 1785-BEM module must be in the same module group (as defined by 2-slot addressing) with the 1785-BCM module.

ATTENTION: Remove power from the 1771 I/O chassis backplane and wiring arm before removing or installing an I/O module.

- Failure to remove power from the backplane or wiring arm could

cause module damage, degradation of performance, or injury.

- Failure to remove power from the backplane could cause injury or

equipment damage due to possible unexpected operation.

4-11

Chapter 4

Installing Your 1785-BEM Module

1. Turn off power to the I/O chassis.

2. Place the module in the plastic tracks on the top and bottom of the

slot that guides the module into position.

3. Do not force the module into its backplane connector. Apply firm,

even pressure on the module to seat it properly.

4. Snap the chassis latch over the top of the module to secure it in

position.

5. Connect the wiring arm to the module.

6. Make wiring connections to the wiring arm as indicated in the next

section.

Connecting Your 1785-BEM Module

Make the Channel 2A and 2B connections to the 1785-BEM module wiring arm (cat. no. 1771-WG) as described in the following paragraphs. Figure 4.7 is an overview of the connections.

4-12

Figure 4.7

assis A

assis B

1785-BEM

Chapter 4

Installing Your 1785-BEM Module

Module Connections

Ch 2A

RIO/DH+

Ch 2B

DH+/ RIO

Clear

Shield

Blue

Clear

Shield

Blue

Clear

Shield

Blue

Shield

Clear

Shield

Blue

Shield

Clear

Ch 2A

Ch 1B

Clear

Shield

Blue

Clear

Shield

Blue

Clear

Shield

Blue

Shield

Clear

Shield

Blue

Replace this with a

terminator if this node is at the end of this physical link.

Blue

Shield

Clear

PLC-5/40

Blue

Shield

Clear

Blue

Shield

Clear

1785-BEM Series A

PLC-5/40

Blue

Shield

Clear

Blue

Shield

Clear

1785-BEM Series A

4-13

Chapter 4

Installing Your 1785-BEM Module

Making Channel 2A Connections

Figure 4.8 shows the Channel 2A connections you must make for your PLC-5 backup system. These connections are between the:

PLC-5/40 or PLC-5/60 processor and the 1785-BEM module two 1785-BEM modules 1785-BEM module and Data Highway Plus network or remote I/O link

Figure 4.8 Channel

2A Connections

Local I/O ChassisLocal I/O Chassis

1785-BCM module 1785-BEM module

PLC-5/40, -5/60, -5/80

1785-BCM module was connected in Chapter 3 but is not shown for clarity.

1. Connect one end of a 1770-CD cable to Channel 2A on one of the

PLC-5/40 or PLC-5/60 programmable controllers, as shown in Figure 4.9.

power supply

Channel 2A

1785-BCM module 1785-BEM module

PLC-5/40 or -5/601771-P4S

Data Highway Plus network or Remote I/O lin k

1771-P4S power supply

19089

4-14

Figure 4.9 Channel

2A Connections Added Between a PLC-5 Processor

and 1785-BEM Module

Chapter 4

Installing Your 1785-BEM Module

Local I/O ChassisLocal I/O Chassis

See Note

Shield

See Note

1785-BCM module

PLC-5/40, -5/60, -5/80

1785-BEM module

1771-P4S power supply

1785-BCM module

PLC-5/40 or -5/60

1785-BEM module

1771-P4S power supply

See Note Shield See Note

Wire channel for either Data Highway Plus or Remote I/O.

Data Highway Plus –connect the signal conductors with Clear, Shield, and Blue insulation to

Remote I/O –connect the signal conductors with Blue, Shield, and Clear insulation to terminals 1,

–

terminals 1, SH, and 2 of PLC –5/40 or –5/60 processor respectively, as well as to terminals 12,

13 and 14 of 1785 –BEM module

SH, and 2 of PLC –5/40 or –5/60 processor respectively, as well as to terminals 12, 13, and 14

of 1785 –BEM module.

2. Connect the other end of the 1770-CD cable to terminals 12, 13, and 14 on the wiring arm of the 1785-BEM module in the same chassis as

shown in Figure 4.9.

3. Perform steps 1 and 2 for the other PLC-5/40 or PLC-5/60 processor and 1785-BEM module.

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4-15

Chapter 4

Installing Your 1785-BEM Module

1785-BCM module

PLC-5/40, -5/60, -5/80

4. Connect a 1770-CD cable to terminals 9, 10, and 11 on each of the 1785-BEM wiring arms as shown in Figure 4.10.

Figure 4.10 Channel

2A Connections Added Between 1785-BEM Modules

Local I/O ChassisLocal I/O Chassis

1785-BEM module

1771 –P4S Power Supply

Channel 2A

1785-BCM module

PLC-5/40, -5/60, -5/80

1785-BEM module

1771 –P4S Power Supply

See Note

Shield

See Note

Wire channel for either Data Highway Plus or Remote I/O.

Data Highway Plus – connect the signal conductors with Clear, Shield, and Blue insulation to

terminals 9, 10, and 11 of 1785 –BEM modules respectively.

Remote I/O – connect the signal conductors with Blue, Shield, and Clear insulation to terminals 9, 10, and 11 of

1785 –BEM modules respectively.

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4-16

Chapter 4

Installing Your 1785-BEM Module

5. Connect the 1770-CD cable from the Data Highway Plus network or Remote I/O link to 9, 10, and 11 on the wiring arm of one of the 1785-BEM modules as shown in Figure 4.11.

1785-BCM module

PLC-5/40, -5/60, -5/80

Figure 4.1 Channel

2A Connections Added Between a 1785-BEM Module

and Data Highway Plus Network or Remote I/O Link

Local I/O ChassisLocal I/O Chassis

1785-BEM module

1771 –P4S Power Supply

Channel 2A

Data Highway Plus network or Remote I/O

1785-BCM module

PLC-5/40, -5/60, -5/80

1785-BEM module

1771 –P4S Power Supply

See Note Shield

See Note

Wire channel for either Data Highway Plus or Remote I/O. Data Highway Plus – connect the signal conductors with Clear, Shield, and Blue insulation to

terminals 9, 10, and 11 of 1785 –BEM modules respectively.

Remote I/O – connect the signal conductors with Blue, Shield, and Clear insulation to terminals 9, 10, and 11 of

1785 –BEM modules respectively.

Making Channel 2B Connections

Figure 4.12 shows the Channel 2B connections you must make for your PLC-5 backup system. These connections are between the:

PLC-5/40, PLC-5/60, or PLC-5/80 processor and the

1785-BEM module two 1785-BEM modules 1785-BEM module and Data Highway Plus or Remote I/O link

19092

4-17

Chapter 4

Installing Your 1785-BEM Module

Figure 4.12 Channel

2B Connections

Local I/O ChassisLocal I/O Chassis

1785 –BCM Module

PLC-5/40, -5/60, -5/80

1785-BCM module was connected in Chapter 3 but is not shown for clarity. Also, 1785-BEM module Channel 2A was previously connected but is not shown for clarity.

1785 –BEM Module

1771 –P4S Power Supply

1785 –BCM Module

PLC-5/40, -5/60, -5/80

Channel 2B

Data Highway Plus network or Remote I/O link

1785 –BEM Module

1771 –P4S Power Supply

1. Connect one end of a 1770-CD cable to Channel 2B on one of the

PLC-5/40, -5/60, or -5/80 processors as shown in Figure 4.13.

19093

4-18

Figure 4.13 Channel

2B Connections Added Between a PLC-5

and a 1785-BEM Module

Chapter 4

Installing Your 1785-BEM Module

Local I/O ChassisLocal I/O Chassis

See Note

Shield

See Note

1785 –BCM Module

PLC-5/40, -5/60, -5/80

1785 –BEM Module

1771 –P4S Power Supply

18 19 20

1785 –BCM Module

PLC-5/40, -5/60, -5/80

1785 –BEM Module

1771 –P4S Power Supply

See Note

Shield See Note

Wire channel for either Data Highway Plus or Remote I/O. Data Highway Plus – connect the signal conductors with Clear, Shield, and Blue insulation to

terminals 1, SH, and 2 of PLC –5/40 or –5/60 processor respectively, as well as to terminals 18, 19, and 20 of 1785 –BEM module.

Remote I/O – connect the signal conductors with Blue, Shield, and Clear insulation to terminals 1, SH, and 2 of

PLC –5/40 or –5/60 processor respectively, as well as to terminals 18, 19, and 20 of 1785 –BEM module.

2. Connect the other end of the 1770-CD cable to terminals 18, 19, and 20 on the wiring arm of the 1785-BEM module in the same chassis as

shown in Figure 4.13.

3. Perform steps 1 and 2 for the other PLC-5/40, -5/60, or -5/80 processor and 1785-BEM module.

19094

4-19

Chapter 4

Installing Your 1785-BEM Module

4. Connect a 1770-CD cable to terminals 15, 16, and 17 on each of the 1785-BEM wiring arms as shown in Figure 4.14.

Figure 4.14 Channel

2B Connections Added Between 1785-BEM Modules

Local I/O ChassisLocal I/O Chassis

1785 –BCM Module

PLC-5/40, -5/60, -5/80

Wire channel for either Data Highway Plus or Remote I/O

Data Highway Plus – connect the signal conductors with Clear, Shield, and Blue insulation to

terminals 15, 16, and 17 of 1785 –BEM module, respectively.

Remote I/O – connect the signal conductors with Blue, Shield, and Clear insulation to terminals 15, 16. and

17 of 1785 –BEM module. respectively.

1785 –BEM Module

1771 –P4S Power Supply

1785 –BCM Module

PLC-5/40, -5/60, -5/80

Channel 2B

See Note

Shield

See Note

1785 –BEM Module

1771 –P4S Power Supply

4-20

19095

Chapter 4

Installing Your 1785-BEM Module

5. Connect one end of a 1770-CD cable to terminals 15, 16, and 17 on the wiring arm of one of the 1785-BEM modules as shown in Figure 4.15.

Figure 4.15 Channel and Data Highway Plus Network or Remote I/O Link

2B Connections Added Between a 1785-BEM Module

Local I/O ChassisLocal I/O Chassis

1785 –BCM Module

PLC-5/40, -5/60, -5/80

Wire channel for either Data Highway Plus or Remote I/O. Data Highway Plus – connect the signal conductors with Clear, Shield, and Blue insulation to

terminals 15, 16, and 17 of 1785 –BEM modules respectively.

Remote I/O –connect the signal conductors with Blue, Shield, and Clear insulation to terminals 15, 16, and 17 of

1785 –BEM modules respectively.

1785 –BEM Module

1771 –P4S Power Supply

Data Highway Plus network or Remote I/O

1785 –BCM Module

PLC-5/40, -5/60, -5/80

Channel 2B

1785 –BEM Module

1771 –P4S Power Supply

See Note Shield

See Note

What to Do Next

19096

6. Connect the other end of the 1770-CD cable to terminals 1, 2, and 3 on the wiring arm of the Data Highway Plus network or remote I/O link as shown in Figure 4.15.

Now that you’ve installed your 1785-BEM module, you are ready to start up your system. Before doing so, double check all connections against the procedures described in this chapter. Chapter 5 describes the operation of the 1785-BCM module and the backup system and shows procedures for starting up and operating your system.

4-21

Chapter

Operating Your PLC-5 Backup System

Chapter Objectives

How the 1785-BCM Module Operates

In this chapter we describe how the primary system transfers data to the secondary system. We do this by describing the operation of the:

1785-BCM module PLC-5 backup system

In addition, we provide procedures for:

starting your system powering up your system disconnecting a faulted system restarting a repaired system changing the processor’s operating mode editing a program on-line

In a PLC-5 backup system, the 1785-BCM module performs three distinct functions:

automatic transfer of remote input data over the High-Speed

Serial Link (HSSL) transfer of data in the data table by block-transfer instructions secondary processor remote programming capability

Automatic Transfer of Remote Input Data Over the HSSL

With automatic transfer, the primary 1785-BCM module is continually updating a copy of the remote input image table in an interface located in the secondary 1785-BCM module. This remote input data includes discrete data as well as block-transferred data. Automatic transfer is carried out over the High Speed Serial Link (HSSL) and is independent of the application program.

The secondary 1785-BCM module responds with current data to the remote I/O scan requests of the secondary processor, making the secondary processor “think” that it is communicating with remote I/O chassis. This response prevents remote I/O faults in the secondary processor, since the secondary processor is not physically connected to the remote I/O link (Figure 5.1).

5-1

Chapter 5

Operating Your PLC-5 Backup System

PLC-5 PLC-5

Figure 5.1 Automatic Transfer of Data Over Remote I/O

HSSL

Primary Secondary

1785-BCM 1785-BCM

Remote I/O

11053I

In addition to providing the secondary processor a copy of the remote discrete input image table, the 1785-BCM modules in both systems work together to provide the secondary processor a copy of block transfer read (BTR) data from the remote I/O chassis.

The primary 1785-BCM module provides the secondary 1785-BCM module with information that a BTW command has been accomplished. The processor can store in memory up to 256 BTW done bits (16 racks x 16 slots=256, maximum) per channel. The primary 1785-BCM module has sufficient memory to store up to 92 BTR instructions of a possible 256 per channel. When the primary processor executes a BTR from any module in a remote I/O chassis, a copy of the data is stored. Should the secondary processor attempt to read that module, it will receive the same data. If the secondary processor attempts to read from a module that the primary processor has not read, the done bit (DN) will not turn on.

Transfer of Data with Block Transfer Instructions

Although not required to implement backup, you can transfer data in the data table by including block transfer instructions to the 1785-BCM module in your application program. We describe transfer of data in the data table by explaining the:

5-2

sequence of transfer method of transfer words in the BTR and BTW instructions used by the PLC-5 backup system input image table auxiliary diagnostics/status words

Chapter 5

Operating Your PLC-5 Backup System

Sequence of Transfer

The sequence of transfer from the primary to the secondary system is as follows:

1. The data from the primary processor’s data table is sent to the primary

1785-BCM module by means of a Block Transfer Write (BTW) instruction.

2. The data is sent to the secondary 1785-BCM module over the HSSL.

3. The secondary processor reads the data from the secondary 1785-BCM

module by means of a Block Transfer Read (BTR) instruction.

Method of Transfer

Data table information is transferred from the primary processor to the secondary processor in a segment that is composed of 1-64 sequentially ordered blocks. Each block has 64 words. The first 2 words of each block are reserved for a system status word and block identification (block ID) word; the remaining 62 are reserved for data.

The content of the block transfer instruction’s first two words depends on the type of instruction (BTW or BTR), and also on the application program run in the primary and secondary processor. Table 5.A briefly describes block transfer instructions in the PLC-5 backup system. (For detailed information about words in the block transfer instructions, refer to the “Block Transfer Read Instruction” and “Block Transfer Write Instruction” sections of this chapter.)

able 5.A

Block Transfer Instructions in the PLC-5 Backup System

Instruction Word Function of word is to:

Primary System Secondary System

1 – System Status inform the processor about the status of the primary and secondary system

Block-Transfer Read 2 – Block Identification

(block I/D)

1 – Number of Blocks in Segment indicate the number of data blocks

Block-Transfer Write

indicate the number of the next block that should be transferred to the module

within a segment being transferred from the processor to the primary 1785-BCM module (1–64). Must be same as secondary system.

indicate the number of the block being transferred from the module

indicate the number of data blocks within a segment being received by the secondary 1785-BCM module (1–64). Must be same as primary system.

2 – Block Identification (block I/D)

indicate the number of the block that is being transferred from the primary processor to the primary 1785-BCM module

reserved for future use

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Chapter 5

Operating Your PLC-5 Backup System

This scheme, where status and block identification information are always present, permits continuous verification of the data transfer, and if necessary, the re-sending of a block of data if that block was not successfully transmitted.

In addition, the 1785-BCM modules exchange the status word over the HSSL continuously (even when the processors are not in RUN mode). This constant communication allows the modules to always have information about each other.

Figure 5.2 shows transfer of data from the primary processor to the secondary processor through the 1785-BCM modules. Note that the path of automatic transfer of remote input data is represented by a dotted line.

Figure 5.2 Transferring in the PLC-5 Backup System

Data W

ith Block Transfer Instructions

Segment

Block 1

(64 words)

Block 2

(64 words)

Block N

(64 words)

PRIMARY SYSTEM SECONDARY SYSTEM

Primary PLC-5 Secondary PLC-5

BTW

#of Blocks in Segment

Block ID

Data

(62 Words)

BTR

Status

Block ID

Primary

1785-BCM

HSSL

Secondary 1785-BCM

BTR

Status

Block ID

Data

(62 Words)

BTW

#of Blocks in Segment

Reserved

•• •••

REM I/O

Segment

Block 1

(64 words)

Block 2

(64 words)

Block N

(64 words)

5-4

Remote Inputs (discrete and analog values)

• sent directly to the primary processor

• transferred automatically to the secondary processor

Remote I/O Chassis

11054I

Chapter 5

Operating Your PLC-5 Backup System

Important: When programming block transfer instructions, you must specify the LENGTH field (Figure 5.3) as 0, since the 1785-BCM module determines that size in accordance with its status (primary or secondary) and type of instruction (BTW or BTR).

Figure 5.3 Block Transfer Instructions

BTR BLOCK TRNSFR READ

Rack Group Module Control Block Data file Length Continuous

N10:100 N10:110

BTW

0 0

0 N

Specify field as 0

BLOCK TRNSFR WRITE Rack

Group Module Control Block Data file Length Continuous

N10:0

N10:10

0 0

0 N

11055I

Block Transfer Read (BTR) Instruction

The local 1785-BCM module provides information to the ladder logic to help coordinate the orderly exchange of information from the primary processor to the secondary processor. The local processor obtains this information by executing a BTR instruction. As shown in Table 5.A, the first two words of the block transfer read (BTR) instruction contain:

status information the current block identification number (block ID)

The BTR in the primary processor transfers only these two words; the BTR in the secondary processor transfers 64 words — the system status and block ID words, plus 62 words of data. Figure 5.4 shows the words of the BTR instruction.

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15 14 13 12 11 10 09 08 07 06 05 04 03 03 01 00

REMOTE ST

Figure 5.4 BTR

Instruction W

ATUS

(IN SECONDAR

ords

BLOCK IDENTIFICA

62 WORDS OF DA

Y PROCESSOR ONL

TION

LOCAL ST

ATUS

Important: The lower byte of the status word is for the LOCAL status. These bits indicate status of the 1785-BCM module installed in the same chassis as the processor to which you are referring. The upper byte of the status word refers to REMOTE status. Its bits indicate the status of the 1785-BCM module installed in the other chassis of the backup system.

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Word 1: System Status — Table 5.B lists the bits in the system status word and defines each.

able 5.B

System

Status W

Status Bit Description

Local

ord Bits (BTR)

0 Serial communication error; when on, this bit indicates a communication

error in the high speed serial link (HSSL)

1 I/O chassis backplane error; when on, this bit indicates a communication

error in the transfer of data from the PLC-5 processor to its 1785-BCM module. Setting bits in the BCM output image table can set this bit.

2 Buffer full; if on, this bit indicates that the primary module cannot accept

writes, or it indicates that the secondary module has received a data block before the first data segment has been read.

3 Programming error; this bit is on when an out-of-range block is detected

between the primary 1785-BCM module and its PLC-5 processor. In the secondary system, this bit is on when the transmitted segment length does not match the received segment length.

If there is a BTW or BTR to the BCM module with an invalid length, the module will not switch over, but this bit will not be on.

4 Remote I/O communication fault; when on, this bit indicates that a

communication fault exists on a remote I/O channel between the processor and the 1785-BCM module. Refer to section “Auxiliary Diagnostics/Status

Words” to know which channel has a communication fault. 5 Reserved – Always 0 6 Primary/Secondary; when on, this bit indicates that the 1785-BCM module

belongs to the primary system; if off, the bit indicates that the module belongs

to the secondary system 7 Data valid; this bit is used only by the secondary processor. If the Fast

Data-Transfer mode is enabled, the bit is on when the 1785-BCM module

contains one data block available to be read. If the Fast Data-Transfer mode

is disabled, the bit is on when the 1785-BCM module contains one complete

segment.

Status DescriptionBit

Remote

Chapter 5

Operating Your PLC-5 Backup System

8 Serial communication error; when on, this bit indicates a communication

error in the high speed serial link (HSSL) 9 I/O chassis backplane error; when on, this bit indicates a communication

error in the transfer of data from the PLC-5 processor to its 1785-BCM

module. See bit 1.

10 Buffer full; if on, this bit indicates that the primary module cannot accept

writes, or it indicates that the secondary module has received a data block

before the first data segment has been read.

11 Programming error; this bit is on when an out of range block is detected

between the primary 1785-BCM module and its PLC-5 processor. In the

secondary system, this bit is on when the transmitted segment length does

not match the received segment length. See bit 3.

12 Remote I/O communication fault; when on, this bit indicates that a

communication fault exists on a remote I/O channel between the processor

and the 1785-BCM module. Refer to section “Auxiliary Diagnostics/Status

Words” to know which channel has a communication fault.

13 Processor fault; when on, the bit indicates that the local system detects a

failure in the remote processor or the remote processor is in PROGRAM

mode

14 Primary/Secondary; when on, this bit indicates that the 1785-BCM module

belongs to the primary system; if off, the bit indicates that the module belongs

to the secondary system

15 Data valid; this bit is used only by the secondary processor. If the Fast

Data-Transfer mode is enabled, the bit is on when the 1785-BCM module

contains one data block available to be read. If the Fast Data-Transfer mode

is disabled, the bit is on when the 1785-BCM module contains one complete

segment.

Important: If the fault is cleared and a successful BTR is executed, the five least significant bits (00, 01, 02, 03, 04) are automatically turned off.

Word 2: Block Identification (Block ID) — Word 2 of the BTR is the block identification word (block ID). Its meaning varies depending on whether it is the primary or secondary system.

In the primary system, word 2 of the BTR instruction indicates the number of the next block to be sent. To calculate this number, the 1785-BCM module adds 1 to the block ID number of the last block that was successfully transferred from the PLC-5 processor to the module through a BTW instruction. If the block is not received successfully, the 1785-BCM module does not increment the last block number. It, however, returns the number of the block in error so that the block can be automatically re-transmitted.

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When the primary 1785-BCM module receives the last block (block ID = number of blocks in segment) through a BTW instruction, the module returns a block number equal to 1 in the next BTR instruction. This re-initializes the data transmission process.

The 1785-BCM module also specifies a block ID equal to 1 under the following conditions:

power-up programming error switchover

In the secondary system, word 2 of the BTR instruction indicates the block number of the data just read, so that the data can be moved to the proper address in the data table. If the Fast Data-Transfer mode is enabled, as soon as the secondary module receives a block, the module sets the data valid bit and releases this block for reading.

If the Fast Data-Transfer mode is disabled, the module returns the data valid bit as a 1 (one) only when the secondary module receives the complete data segment. This means that the data valid bit remains on until the last block is read from the secondary 1785-BCM module. If no blocks are available to be read, the 1785-BCM module returns the block ID as 0 (zero) and the file contains only two words (status and block ID).

Block Transfer Write (BTW) Instruction

The local processor sends information to the 1785-BCM module using the BTW instruction. In the backup system, the block transfer write (BTW) instruction uses the first two words to indicate:

the number of blocks in the segment being sent the block identification number (block ID)

The BTW in a primary system transfers these two words, plus 62 words of data; the BTW in the secondary system transfers only these two words of data. Figure 5.5 shows the words of the BTW instruction.

5-8

Figure 5.5 BTW Instruction W

Chapter 5

Operating Your PLC-5 Backup System

ords

15 14 13 12 11 10 09 08 07 06 05 04 03 03 01 00

NUMBER OF BLOCKS IN SEGMENT

TION

Reserved for future use

BLOCK IDENTIFICA

62 WORDS OF DA

(PRIMAR

Y PROCESSOR ONL

Word 1: Number of Blocks in Segment — In the BTW instruction, word 1 has different meanings depending on whether the system is primary or secondary. The number of blocks in a segment should be the same in both processors. (The secondary 1785-BCM module checks this word to make sure it matches the number of blocks specified in the primary.) If not, the programming error bit (local — bit 3, remote — bit 11) will be on in the system status word.

In the primary system, word 1 of the BTW instruction indicates the total number of blocks that make up the data package being transferred.

In the secondary system, word 1 of the BTW instruction indicates the number of blocks that make up the package to be received.

Bits

ord 1 Word W

ord 3 . . . W

ord 64

11057I

Word 2: Block Identification (Block ID) — Word 2 of this instruction is called the block identification (block ID) word. Its meaning varies depending on whether the system is primary or secondary.

In the primary system, the word is reserved for the identification number of the block being sent.

Important: It is your responsibility to make sure that each data block you want to send has its own unique identification number.

In the secondary system, word 2 is not used and is reserved.

Auxiliary Diagnostics/Status Words

The 1785-BCM module appears to the PLC-5 processor as a 32-point I/O module. This means that the I/O chassis physical slot in which the module is located corresponds to two input and two output image table words.

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With 1785-BCM module, 32 input bits are available in the PLC-5 processor image table. (The 32 output bits in the output image table are unused and reserved.) These input words are called Auxiliary Diagnostics/Status Words and they provide further information about the 1785-BCM module and the 1785-BEM backup expansion module in both the primary and secondary systems. Refer to Figure 5.6.

Figure 5.6 Auxiliary

Diagnostics/Status W

ords

W1 Bits:

Bits 00 to 07 = Reserved for Block Transfer Communication Bit 10 = 1785-BCM series A module Bit 11 = Fast Data Transfer mode Bit 12 = Reserved Bit 13 = Reserved

W2 Bits:

Bits 00 to 07 = 1785-BEM module communication channels status Bits 10 to 17 = 1785-BCM module communication channels status

1 2

Channel 1A Status

Note that these bits are in octal format because they correspond to the input image table. Bits

00 to 07 of the second word can be used or not, depending on whether the 1785-BEM module is in

the backup system or not.

Channel 1B Status

Channel 2A

Status

RESERVEDEXTENDED STATUS

Channel 2B

Status

Bit 14 = Reserved Bit 15 = Reserved Bit 16 = Switchover Diagnostic Bit 17 = 1785-BEM module

1st Word

2nd Word

11058I

The first word address corresponds to the module slot, that is, the location of the 1785-BCM module in the I/O chassis. The least-significant byte of this word is reserved to the 1785-BCM module usage and the most-significant byte shows extended status of the module. Refer to Table 5.C.

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ÉÉ

Operating Your PLC-5 Backup System

able 5.C

Extended

Bit

Status Bits (W1)

10 1785-BCM series A module; when on, this bit indicates that the other 1785-BCM module is

series A.

11 Fast Data Transfer mode; when on, this bit indicates that the data valid bit is set to 1 (one)

as soon as the secondary module receives a data block. When off, this bit indicates that the data valid bit is 1 (one) only when the secondary module receives the complete data

segment. 12 Reserved – always 0 13 Reserved – always 0 14 Reserved – always 0 15 Reserved – always 0

Description

16 Switchover Diagnostic; this bit is always off, but if during a switchover condition this bit is

on, it means that the module must be replaced. 17 1785-BEM module; this bit is on when there is a 1785-BEM backup expansion module in

the system.

Bits 0 through 7 (least significant byte of W1) are unused and reserved. For W1, bit 0 is the

least-significant bit and bit 17 is the most-significant bit.

The second auxiliary status word address corresponds to the right-most slot of the first I/O module group in the I/O chassis. This word shows the channel configurations of the 1785-BCM and 1785-BEM (if any) modules and also indicates an error condition in any of these channels.

The most-significant byte of this word corresponds to Channels 1A and 1B of the 1785-BCM module. The least-significant byte corresponds to Channels 2A and 2B of the 1785-BEM module. Refer to Figure 5.7.

Figure 5.7 Second

Auxiliary Diagnostics/Status W

ord

07 10 03 04 13 14 17

= error bit per channel

Channel 1A

Error

Bit

Channel 1B Channel 2A Channel 2B

11059I

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Each byte of word W2 is divided into two groups of four bits corresponding to the module’s channels (Figure 5.7). The three least-significant bits of each group corresponds to three switches of switch assembly SW2 which is used to specify the configuration of module channels. The most-significant bit corresponds to the error bit for the respective channel.

Refer to Chapter 8, Diagnosing Faults, for further information about these bits of the Auxiliary Diagnostics/Status Words.

Secondary Processor Remote Programming

Important: The programming device must be connected through the Data Highway Plus network and must not bypass the relay in the 1785-BCM module. If you were to connect the device directly to a processor, it must be

connected to the primary processor. Therefore, if your system were to switch to the secondary system, you must then move your device to your new primary processor.

In the PLC-5 backup system, only the primary processor is connected to the link. The secondary processor is not physically connected, but it communicates with the secondary 1785-BCM module making this processor think that it is on the Data Highway Plus network. This separate link prevents Data Highway faults in the secondary processor.

The 1785-BCM series B backup module provides remote programming capability for your secondary processor. This means that even with the programming device directly connected to the primary processor, the secondary PLC-5 processor memory can be programmed and/or monitored.

Important: If you are communicating with the primary processor via a programming terminal, do not place it in Remote Program mode. If you do, a switchover will occur and the new primary can go into Remote Program mode, shutting the system down.

Important: As a guideline, you should connect over DH+ to only one programming terminal at a time on the secondary processor.

The primary 1785-BCM module provides an access point for a programming device to access the secondary processor. Using the 1785-BCM module, you can communicate from a programming device across the backup modules to the secondary processor. You must assign both the primary and the secondary processor the same node address (using either dipswitches or Channel Config screen in 6200 software) in the Data Highway Plus link. The 1785-BCM module reserves the subsequent node address as an access-point address to the secondary processor, that is, this address is accessed by a programming device in order to program the secondary processor.

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This means that if you set both processors node addresses to n, the programming device can communicate with the secondary processor with the node address n+1.

For example, a primary processor with node number 16 on Data Highway Plus network has the same address switch setting as the secondary processor node. However, in this situation, the terminal addressed to station 16 attaches to the primary processor and the terminal addressed to station 17 attaches to the secondary processor.

Important: It is recommended to assign the same node address (n) for both processors (primary and secondary) in a redundant system. You must also reserve the next node address (n+1) because this address is the access-point address to the secondary processor.

Figure 5.8 shows how the programming device sees the secondary processor which is not physically connected to the Data Highway Plus link.

Important: The DH+ connection to the secondary processor is meant for remote programming only. Also, only one terminal at a time may connect to the secondary processor. No DH+ messages can be sent to or from the secondary processor.

Figure 5.8 Access

Point to the Secondary Processor (DH+)

Node address = n + 1Node address = n

PLC-5

n n

BCM BCM

HSSL

Programming Device

PLC-5

DH+

11060I

How the Backup System Operates

When the system is started, each PLC-5 processor executes a BTR instruction to its 1785-BCM module to obtain the system status word, which will indicate whether it is in the primary or secondary mode. If the processor belongs to the primary system, it will execute the primary (transmitter) program; if the processor is secondary, it will execute the secondary (receiving) program.

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To provide status information, or to pass additional block transfer values, you must provide support ladder programming. Refer to Chapter 7, “Programming Techniques” and Appendix A “Sample Programs” for information on developing ladder programs for the backup system.

Primary (Transmitter) Program

Upon initialization of the backup system, or when the secondary PLC-5 is not in operation, the primary 1785-BCM Module responds to the BTR instruction that the block number is one (block ID = 1). This assures the correct initiation of the block transfers, principally when the secondary PLC-5 is placed in RUN mode.

After execution of the first BTR instruction, the 1785-BCM module is ready to execute the necessary sequence of instructions to transfer the data table words from the primary system to the secondary.

Important: Remember that, in block transfer instructions, you must specify the LENGTH field as 0 (zero). This allows the 1785-BCM module to determine automatically the block size depending on if the module is in the primary or secondary system. In the primary system, the 1785-BCM module will return 2 words in the BTR instruction, while the processor will write 64 words to the 1785-BCM module.

Each word received by the primary 1785-BCM module is stored in its buffer. If the primary module receives the data block (of up to 64 words) without errors, it automatically sends the block to the secondary 1785-BCM module over the HSSL. Each block is checked for errors, and if no errors are pending, the primary module transmits the data after the current data block, one block at a time.

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Figure 5.9 Execution

Chapter 5

Operating Your PLC-5 Backup System

of Primary Program

Primary Processor

BTR

words

Block ID = 1

BTW

64 words

Primary 1785-BCM module

1. At program initialization, 1785-BCM module specifies block ID of 1 so that BTW are initiated in correct sequence.

3. When primary 1785-BCM

2. Primary processor sends data to primary 1785-BCM module. The module stores this data in its buffer.

Buffer

module receives data block without errors, it sends data to secondary 1785-BCM module over the HSSL.

o secondary 1785-BCM

11061I

Secondary (Receiver) Program

In the secondary program, the BTR instruction is used to obtain the system status, the block ID word, and its respective data. The BTW instruction informs the secondary 1785-BCM module of the size of the segment to be received, that is, the number of blocks which must be accepted before turning on the data valid bit.

The number of blocks which must be accepted before turning on the data valid bit depends on the switch setting for Fast Data-Transfer mode and word 1 of the BTW segment length.

The secondary PLC-5 processor will read data from the secondary 1785-BCM module according to the Fast Data Transfer mode setting.

Fast Data-Transfer Mode Enabled

The secondary PLC-5 processor continuously executes BTR instructions to obtain the system status word and data from the secondary 1785-BCM module. With the Fast Data Transfer mode, as soon as the secondary 1785-BCM module correctly receives a data block, the data valid bit returned to its local processor through the BTR instruction will immediately turn on and the block is released for reading.

Fast Data Transfer Mode Disabled

The secondary PLC-5 processor continuously executes BTR instructions to obtain the system status word and data from the secondary 1785-BCM module.

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The primary 1785-BCM module sends several data blocks that make up a segment sent to the secondary 1785-BCM module. Until the secondary 1785-BCM module correctly receives all blocks of the segment, the data valid bit returned to its local processor through the BTR instruction will not turn on. This bit will turn on only when the complete segment is correctly received and the number of blocks in the segment match that sent by the primary 1785-BCM module. Transfer from the 1785-BCM and the secondary processor can now begin.

During transfer of the information from the 1785-BCM module to the secondary processor, the 1785-BCM module sets the block ID of the first block equal to one and increments it on each successive block.

In the BTR data, the block ID word always contains the number of the last block received from the buffer of the 1785-BCM module. If the buffer is empty, or if the 1785-BCM module cannot send a new segment, the block ID equals 0 (zero) and only the first two words are received. Figure 5.10 shows how the secondary program operates.

From primary 1785-BCM

Figure 5.10 Execution

Secondary 1785-BCM Module

Buffer

Important: It is up to you to:

determine which parts of the data table must be shared by the processors

of the Secondary Program

1. Processor executes BTW to tell 1785-BCM module the length of segment to be read.

2. Processor detects a data block in the secondary 1785-BCM module with a block ID of 1.

3. Processor executes BTR instructions to receive data blocks from the secondary 1785-BCM module.

Secondary Processor

BTR

words

BTW

2 words

Segment Length

11062I

5-16

develop a program that sequences all blocks to and from the 1785-BCM

modules

account for the asynchronous nature of queuing and moving of BTW and

BTR data in the PLC-5 processor.

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Operating Your PLC-5 Backup System

For example, if the primary processor is sending multiple blocks to the secondary processor, the data that was in block 2 when block 1 was sent may change by the time block 2 is sent. This is because the ladder program, which executes asynchronously to block transfer instructions, may have changed the information in block 2 before it was sent.

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Starting the Backup System

After you have checked your program for proper data to be transferred, and have developed the transmitting and receiving programs, you can start the backup system.

To start the backup system:

1. Apply power to the primary system.

2. Apply power to the secondary system.

3. Load the application program and the remote I/O configuration in the primary PLC-5 processor by addressing node n.

4. Test the system.

5. Load the application program and the remote I/O configuration in the secondary PLC-5 processor through node n+1.

6. Test the system.

7. Switch the primary and the secondary PLC-5 processors to RUN mode.

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Powering Up the Backup System

If a power loss occurs in both the primary and secondary systems once the backup system has been started up, use the following power-up sequence:

ATTENTION: When you connect a 1785-BCM series B module to a 1785-BCM series A module, ensure you have properly set switch 1 of switch assembly SW1. Otherwise, if you power up both systems, both modules will assume to be the primary.

1. Switch both PLC-5 processors to PROGRAM mode.

2. Re-apply power to the system that you intend to be primary.

3. Switch the primary PLC-5 processor to RUN mode.

4. After the primary PLC-5 processor begins operating correctly, re-apply

power to the secondary system.

5. Switch the secondary PLC-5 processor to RUN mode.

If you power up both systems at the same time, the 1785-BCM modules decide which will be the primary and which the secondary. In this case, all of the relays of the modules remain open until one of the 1785-BCM modules arbitrarily assumes control of the process. This guarantees the existence of only one primary system.

Disconnecting/Repairing a Faulted Backup System

When a fault occurs in the primary system, the remote I/O, Data Highway Plus, and customer relay switches in the primary 1785-BCM module open immediately. When these switches open, the module interrupts the transmission of data and sends commands to transfer control to the secondary module.

Because the secondary PLC-5 processor’s input image table has been loaded with actual data from the primary processor’s remote I/O interface, the application program of the secondary processor does not need to wait for the complete execution of an remote I/O scan to use this input image table data.

After 50 ms maximum, the remote I/O, Data Highway Plus, and customer relay switches in the secondary 1785-BCM module close. When these switches close, the secondary PLC-5 processor is now controlling the system and becomes the primary processor.

To disconnect a faulted backup system, do the following:

1. Power-down the faulted system.

2. Troubleshoot and/or repair the faulted system as needed.

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Restarting a Repaired Backup System

Switching the Processor’s Operating Mode

Once a faulted system has been repaired, you may restart it as described below. You do not need to power-down or change the mode of the operating system to restart the system.

1. Switch the repaired processor to PROGRAM mode and apply power. This way, the processor automatically becomes the secondary (backup).

2. Load the memory of the secondary processor and the I/O configuration through node n+1 by using a programming device connected to the Data Highway Plus link.

ATTENTION: Ensure that key data table values are identical in both processors. If this is not accomplished, unpredicted machine motion could result when you transfer from primary to secondary processor.

3. Switch the backup processor to RUN mode.

The 1785-BCM Backup Control Module does not control the operating mode (PROGRAM/RUN) of the primary and secondary PLC-5 processors. Thus, if it is necessary to change the operating mode of the processor, change the mode of the secondary processor first. Then change the mode of the primary processor.

Always change the mode of the secondary system first; if both processors are in RUN mode, and if the primary processor is switched to PROGRAM mode first, the primary processor transfers control of the I/O to the secondary system.

Remote Test-Mode

To initiate remote test-mode on a processor in backup configuration (using a 1785-BCM series B module), perform the following steps.

1. Take the secondary processor off-line by removing power or placing the secondary processor in program mode.

2. Initiate the remote-test mode command to the primary processor.

When the primary processor is in remote-test mode, the outputs are disabled.

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Editing or Programming On-line

What to Do Next

To avoid a control switch from the primary to the secondary processor when you attempt to edit the ladder program or data table of the primary PLC-5 processor using a programming device:

1. Do not switch the primary PLC-5 processor to REMOTE PROGRAM mode. Switch the primary PLC-5 processor to REMOTE RUN mode.

Important: If you switch the primary processor to REMOTE PROGRAM mode, the processor transfers control to the secondary processor. In most cases, the new primary then switches to Remote Program mode, shutting the system down.

2. Make edits in the secondary processor first. However, make sure that all necessary changes are made in both processors.

Important: Using the on-line editing/programming function can cause the primary and secondary systems to diverge if the system should switch before you complete the edits in both processors.

This chapter described the basic operation of the 1785-BCM modules and the PLC-5 backup system, and gave you procedures for operating your module. Read the next chapter to learn how the backup system operates at switchover, and how you need to account for this when programming your system.

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Chapter

Switchover Considerations

Chapter Objectives

Timing Requirements

When planning programs for the PLC-5 backup system, you must first consider that the program scans of the two processors are not synchronized; that is, the program in the primary processor is not executing the exact same instruction at the same time as the program in the secondary processor. In addition, you must consider:

timing divergence I/O forces Data Highway Plus switching remote I/O switching special sections of the data table data integrity

This chapter describes these switchover considerations. This chapter also describes switchover diagnostic. It describes how to detect a possible fault in the secondary module and how to consequently avoid switchover problems in the backup system.

Although switchover from one processor to the other is fast — less than 50 ms, it does not happen instantly. Make note also that the total switchover time is a factor of the 1785-BCM module delay, plus, at worst case, one program scan of the secondary processor. The time of one program scan is added because the secondary processor technically has not assumed control until one scan of its program and remote I/O after the switchover.

When a failure occurs in the primary system, the remote outputs remain in the state set by the primary processor prior to switchover, as well as while the secondary processor assumes control of the process. Keeping this in mind, you must program the backup system to account for the following time requirements:

input signal update time time-out on remote I/O link data table transfer time over the HSSL

6-1

Chapter 6

Switchover Considerations

Input Signal Update Time

Immediately after the switchover, it is possible that the secondary processor will be reading different input conditions. To avoid a sudden change in the outputs during switchover, all of the input signals must be present for at least a time equal to the sum of:

program scan I/O scan input module delay 1785-BCM switchover time

If these conditions are not met, outputs may be assigned different states in the two processors. This can cause a sudden change of operation when switchover occurs.

Time-out on Remote I/O Link

The remote I/O chassis are updated one at a time. The total remote I/O update is 10 ms per chassis (typical).

To keep the I/O chassis from faulting and losing control of the I/O, the switchover in the remote I/O link (the time from when the remote I/O relays in the primary 1785-BCM module open to when the remote I/O relays in the secondary 1785-BCM module close) will be accomplished in less than 50 ms. (The 1785-BCM module will do this automatically.)

This switchover time is less than the 100 ms for remote I/O adapter watchdog timeout; therefore it allows continuous control of the I/O from the backup system processors.

Data Table Transfer Time

This time refers to the time it takes to transfer critical data from the primary system to the secondary system. Data table transfer time is dependent on the amount of data to be sent between the two systems, the number of remote I/O chassis, and the number of remote I/O block transfers that are being executed.

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Chapter 6

Switchover Considerations

Using the 1785-BCM module, the primary system can transfer data to the secondary system at a maximum throughput of 4K words in less than 1 second. This time takes into account:

program scan programming method used to transfer data to secondary processor PLC-5 block-transfer queuing number of remote I/O chassis number of remote I/O block transfers

For actual data table transfer times when transferring different block lengths of data, refer to Appendix A “Sample Programs.”

Divergence

The program scans are not synchronized; therefore, it is possible that the processors read the same inputs and control outputs accordingly, but at slightly different times. Sometimes, the processors will read different input values and make different decisions. This means that the internal states of the two systems may diverge.

If the two systems diverge, the secondary system generates a bump when it takes control of the process. Like data table transfer time, the duration of this bump is a function of how fast the inputs of the machine or process are changing, as well as the amount of data to be sent between the two systems.

To limit divergence, we recommend that the primary and secondary processors execute the same programs.

Important: When you use outputs (from 0 file) to seal-in a rung with non-retentive output instructions, the seal-in will be lost if the processors switch primary and secondary twice, consecutively. This occurs because a PLC-5 processor, when powering-up, going from PROGRAM to RUN mode, or clearing a fault, resets outputs and performs a prescan to force all rungs false before going into RUN mode. This turns off all output bits controlled by non-retentive output instructions. This will cause divergence between the primary and secondary processors.

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Switchover Considerations

Forcing

I/O

Data Highway Plus Switching

Backup communication functions provided by the PLC-5 backup system do not transfer the force tables from the primary to the secondary processors. Thus, if the PLC-5 backup system has forces set in the primary processor, the forces do not transfer to the secondary processor. For this situation, if a switchover occurs, the secondary processor becomes active, but the forces set in the original primary processor are not carried over.

ATTENTION: Set the forces in the secondary processor first and then in the primary processor. Likewise, when removing forces, remove forces in the secondary processor before removing the forces in the primary processor.

If a switchover occurs and forces were not set in the secondary processor first, the secondary processor would not recognize the forced-on input or output.

In the Data Highway Plus link, one station on the link has control of the link at a time. The station with this control is referred to as the station that has the “token.” In the PLC-5 backup system, only the primary processor is connected to the link. But, the secondary processor communicates with the secondary 1785-BCM module, making this processor think that it is on the Data Highway Plus network.

6-4

The secondary processor can be programmed through an access-point address which corresponds to the processor node address plus one (n+1). The secondary processor becomes part of the link only after a switchover.

It is possible that the primary processor could have possession of the token during a switchover from the primary to the secondary processor. If this is the case, the token could be lost even though passage of the token from one station to the next is done as quickly as possible.

If the token is lost, all the stations on the link have an internal watchdog timeout (250 ms), and the nodes assume the token is lost.

Chapter 6

Switchover Considerations

The other stations on the link initiate a token recovery procedure which includes:

recreating the active node table rebuilding the link, including the new primary processor ensuring that one node gains control of the link

During this time, while the stations reconstruct the link, communication is interrupted. The length of this time depends on the number of stations involved in the link, and the number of messages received and/or transmitted. (This time is typically less than 50 ms per station).

However, while the link is rebuilding, messages can collide, increasing the amount of time needed to reconstruct the link. As a result, on a typical Data Highway Plus link with 6 – 10 stations, the impact on the link due to switchover could be the loss of communication for as much as 1 – 3 seconds.

Data Highway Plus switching occurs whenever there is a transfer of control from the primary to the secondary processor. The switchover could result from a power failure or because of other system failures. Table 6.A shows what can happen to the link if the token is lost.

Important: Note that when a transfer of control from the primary to the secondary processor occurs, the processor that is now primary has the node address of n on the DH+ link. The processor that is now secondary has the node address of n +1.

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Chapter 6

Switchover Considerations

able 6.A

DH+

Switchover Scenarios

If the new primary is: the following could occur causing this result

Polling the link Message packet from another station

disrupted

Reply packet disrupted Same as above Token pass packet disrupted The DH+ link times out and must rebuild. (250

Listening to the link New primary processor takes the

token

New primary processor receives a message from another station

The source station turns on error bit in its MSG instruction (You provide programming at the source station to regain synchronization with the receiving station. You can do this by monitoring the message instruction error bit as a condition for re-transmitting the message.)

ms watchdog timeout) + (50 ms x number of stations on the link).

The new primary processor has nothing in its active node table. The DH+ link times out and must rebuild. (250 ms watchdog timeout) + (50 ms x number of stations on the link).

The link continues working normally

Programming

Remote I/O Switching

Important: In the recommended configuration, set both PLC-5 processors to the same station address. The backup modules permit only one of the two processors to be connected to the Data Highway Plus at a time. In this configuration, remote PLC processors and operator stations communicate to the processor that currently has primary status. Note that the secondary processor can also be accessed through the primary PLC-5 processor node address plus one (n+1).

The communications protocol for the remote I/O link is a master-slave half-duplex type. This means that the master station (processor) sends a command message addressed to a slave (remote I/O adapter), and the slave responds with a reply message addressed to the master. This is also called two-way alternating communication.

When the backup system is operating properly, the relays of the primary 1785-BCM are closed and the relays of the secondary 1785-BCM are open. Should a failure occur in the primary system, the relays of the primary 1785-BCM module open and the relays in the secondary 1785-BCM module close.

6-6

Chapter 6

Switchover Considerations

The secondary processor (remote I/O scanner or adapter) is not part of the remote I/O link, but is communicating with the secondary 1785-BCM’s smart switch interface. When the secondary processor is configured for scanner mode, this interface responds to a poll from the secondary processor’s scanner with actual data it receives from the primary processor over the HSSL. The scanner “thinks” that it is communicating with the real remote I/O adapters. The function of the interface is to respond to the secondary processor with current data from the primary processor, enabling the input image table of the secondary processor to be a copy of that of the primary processor.

Similarly, when the secondary processor is configured for adapter mode, the 1785-BCM module polls the secondary processor’s adapter, updating the input image table of the secondary processor to be a copy of that of the primary processor. Also, a BTR can be performed in the secondary processor to receive data from the supervisory processor.

Important: The smart-switch interface communicates with the secondary processor only when the 1785-BCM module belongs to the secondary system. When the module is primary, the smart switch only monitors the remote I/O link to obtain input/output data.

The smart switch interface also includes a carrier-detect circuit to monitor the activity of the remote I/O link. The purpose of this circuit is to detect an idle remote I/O link before the secondary relays are closed. This guarantees that the former primary system was really disconnected from the link and the remote adapters have completed their response to the last poll from the primary scanner.

In addition, in the event of an HSSL break, the carrier-detect circuit prevents the secondary system from taking control of the link along with the primary system. Figure 6.1 shows the block diagram of the remote I/O switch.

6-7

Chapter 6

Switchover Considerations

Figure 6.1 Block

Diagram of Remote I/O Switch

HSSL link (to primary 1785-BCM

1785-BCM

Copy of remote I/O data including block transfers

Smart-switch

Remote I/O link

Secondary processor I/O scanner/adapter

Carrier-detect circuit

To determine the maximum time it takes for the secondary module to close its relays after it detects a switchover, consider the following:

the primary scanner has just requested a 64-word BTR from the remote

module at 57.6 kbaud

the remote adapter starts to respond switchover is triggered

You can calculate the maximum time for the I/O link switchover as follows:

1. remote I/O communication rate = 57.6 kbits/s = 1 byte/.14 ms

2. transfer time = 64 x 2 x .14 = 18 ms

interface

11106I

6-8

3. HSSL protocol overhead/BCM delay = 12 ms

4. 1785-BCM module remote I/O watchdog timeout = 20 ms Maximum time = 18 + 12 + 20 = 50 ms

Note that this time is less than the 100 ms remote I/O adapter watchdog timeout, and therefore allows for continuous control of the I/O from the backup system processors.

Chapter 6

Switchover Considerations

Data Table Considerations

Several of the data table sections in the PLC-5 processor are not structured with single 16-bit words. You need to consider this when applying the 1785-BCM module.

For example, the BTW of the primary processor transfers 62 words of data to the secondary processor (plus the packet length and block ID word). Some structures such as timers, counters, and floating point control files have three words. If all related words don’t fit in a block, some words may be truncated, creating a partial structure in the secondary processor (Figure 6.2).

Figure 6.2 Partial

Structure in BTW

BTW (64 words)

ord 1

ord 2

ords 3 – 62

Packet Length Block ID

. . .

o secondary

Counter

W W

ord 63 ord 64

ord 65

Control Word

Preset value

Accumulated value is truncated

Problem structures include:

timer values counter values floating point elements control registers

11107I

6-9

Chapter 6

Switchover Considerations

Because the secondary processor’s program scan and block transfer execution are totally asynchronous, it is possible for the secondary processor to operate on partial data structures. If the secondary processor is executing instructions that operate on any of the multi-word structures that are listed above, the following sequence of events may occur:

1. The 1785-BCM transfers the first word of a multi-word structure to

the secondary processor. A partial data structure temporarily exists in the secondary processor.

2. The secondary processor operates on this partial structure and derives

invalid results.

3. The partial data structure and the invalid result of the operation exist

in the secondary processor until the remaining portion of the structure is transferred. The secondary processor re-executes the operation on the next program scan and overwrites the invalid result with the correct result.

Data Integrity

4. If the primary processor were to go de-active before the invalid result

of the processor operation was corrected, then the invalid results would persist in the secondary processor for an indeterminate period of time.

Important: To prevent partial structures from occurring in the secondary processor, you must group related data words or multi-word elements (i.e. floating point) so that they fit in one block.

Some of the PLC-5 processor instructions operate on data structures with less than 16-bit words. These other data structures are:

bits bytes bit fields

Instructions such as bit-shift and bit-distributor instructions use these other data structures. When using these instructions, you must be aware that the data table will contain invalid data until the processor executes a series of instructions. For example, if you are shifting four bits of BCD data through several words bit by bit, the data table will contain invalid data until each shift is complete.

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Chapter 6

Switchover Considerations

Should the 1785-BCM module transfer one or more of these values to the secondary system and the primary system fails, the data table of the secondary system will contain intermediate values for an indeterminate amount of time, thus creating illegal BCD values.

Important: Because block transfer instructions operate asynchronously to the execution of the program scan, we suggest using the condition of the done bit (DN) of the BTR or BTW instruction as part of the logic used to initiate the transfer when using block transfer instructions to move data from the primary to the secondary 1785-BCM module. Figure 6.3 shows typical rungs that use the condition of the done bit to initiate a transfer. Refer to appendix A, “Sample Programs” to see these types of rungs used in a program.

Figure 6.3 Typical

Data Move Rungs

BTR

BTW

—> B

DATA

Check Block ID

VALID

Check Block ID

Move Data

B —> A

Move Data

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Switchover Diagnostics

The 1785-BCM backup module continuously executes an internal hardware diagnostics routine to ensure that it is operating correctly. In the case that a primary module detects a major fault like bad RAM memory or bad CPU, its relays will immediately open and a switchover will automatically occur.

Check if the 1785-BCM module is operating correctly and avoid problems in case of an eventual switchover in the backup system by executing a manual switchover when it is possible. If a minor fault is detected during this manual switchover, the module will switch. In addition, it will also turn on the switchover diagnostic bit (bit 16) of the extended status word, indicating that the module should be replaced as soon as possible. Refer to the section in Chapter 8, Diagnosing Faults with Bits of the Auxiliary Diagnostics/Status Words, for further information.

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Chapter 6

Switchover Considerations

What to Do Next

In this chapter, you read about switchover considerations for the PLC-5 backup system. By accounting for these considerations in your program, you can execute a smoother and faster switchover should the primary processor fault. Read the next chapter to learn about two different programming techniques you can use when you program your PLC-5 backup system. Read also to learn about program instructions that can cause problems during switchover.

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Chapter

Programming Techniques

Chapter Objectives

Getting Started

Read this chapter to familiarize yourself with techniques used to program your PLC-5 backup system.

In this chapter we describe:

how to get started with a program to transfer data table values

two methods you can use to program the PLC-5 backup system to transfer

data table values

the behavior of specific instructions when used in your application program,

and give you suggestions for dealing with these instructions.

The 1785-BCM modules control switchover and transfer remote I/O data without additional programming. However, if you want to transfer data table values from the primary to the secondary processor, you must provide a ladder program. Figure 7.1 shows the minimum ladder programming you must provide to transfer 62 words of the data table between the two 1785-BCM modules, and to provide 1785-BCM module status. You need to put this program in both processors.

7-1

Chapter 7

Programming Techniques

1771–BCM GETTING STARTED PROGRAM 1 April 1995 Page 1 Program Listing Report PLC–5/25 Addr 1 Rung 2:0

Rung 2:0 | NUMBER OF | | SEGMENTS | | STORE WORD | | | | +MOV–––––––––––––––+ | +–––––––––––––––––––––––––––––––––––––––––––––––––––––––++MOVE ++–+ | ||Source 1|| | | || || | | ||Dest N10:1|| | | || 1|| | | |+––––––––––––––––––+| | | | BID | | | | WORD | | | |+MOV–––––––––––––––+| | | ++MOVE ++ | | |Source 1| | | | | | | |Dest N10:2| | | | 1| | | +––––––––––––––––––+ |

Figure 7.1 Minimum

Program to T

ransfer Data T

(put this program in both processors)

able Values

7-2

Rung 2:3 | | +––––––––––––––––––––––––––––––––[END OF FILE]–––––––––––––––––––––––––––––––––+ | |

Chapter 7

Programming Techniques

Programming Methods to Transfer Data Table Values

This manual provides two solutions to programming your PLC-5 backup system to transfer data table values. These methods are:

transferring data one block at a time transferring data multiple blocks at a time

We describe the operation of these programming methods on the following pages. To view sample programs that use these methods, refer to appendix A, “Sample Programs.”

Method 1 — Transferring Data One Block at a Time

In the first programming method, transferring data one block at a time, both the primary and the secondary processors execute and scan identical programs. This method requires that you execute BTR and BTW instructions on alternate program scans. You are able to do this because the primary 1785-BCM module has the ability to identify and increment the block ID by one. (For more information about the block ID, refer to Chapter 5, “Operating Your PLC-5 Backup System.”)

Using this method, your application program can use the block ID returned in the block transfer read (BTR) instruction to control the data file of the block transfer write (BTW) instruction control file.

This method of programming results in a slower overall throughput of data transfer, but gives tighter control of the transfer, allowing automatic re-transmission of a block if an error in the transfer should occur.

A program that uses this method contains:

A BTW and BTR instruction in each PLC-5 processor. These instructions

should be of a free-running nature and be the same in both the primary and secondary processors.

A chained series of File Copies (COP).

Program operation varies depending on if the system is primary or secondary. The primary 1785-BCM module executes a 64 word BTW instruction and a 2 word BTR instruction; the secondary 1785-BCM module executes a 2 word BTW instruction and a 64 word BTR instruction.

7-3

Rockwell Automation 1785-BCM, 1785-BEM, D17856.5.4 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Important User Information

Summary of Changes

Manual Objectives

Audience

What this Manual Contains

Terms and Conventions

Related Publications

Table of Contents

Chapter Objectives

Why Use a Backup System?

Applying 1785-BCM Backup Communication Modules to the PLC-5 Programmable Controller

What to do Next

Chapter Objectives

Status Indicators

Wiring Arm

Communication Links

Customer Relay

Chapter Objectives

PLC-5 Backup System Installation Overview

Determining Power Supply Requirements

Setting the I/O Chassis Switches

Terminating the Data Highway Plus and Remote I/O Links

Installing the 1785-BCM Module

Connecting Your PLC-5 Backup System

What to Do Next

Chapter Objectives

Backup Expansion Module

Hardware Components

Determining Power Supply Requirements

Connecting Your 1785-BEM Module

Chapter Objectives

How the 1785-BCM Module Operates

How the Backup System Operates

Starting the Backup System

Powering Up the Backup System

Disconnecting/Repairing a Faulted Backup System

Restarting a Repaired Backup System

Switching the Processor’s Operating Mode

Editing or Programming On-line

What to Do Next

Chapter Objectives

Timing Requirements

Divergence

Data Highway Plus Switching

Programming

Remote I/O Switching

Data Table Considerations

Data Integrity

What to Do Next

Chapter Objectives

Getting Started

Programming Methods to Transfer Data Table Values