1785 - BCM /C Allen Bradley Modular PLC-5 Backup Communication Module

New Allen Bradley 1785-BCM /C PLC-5 Back-Up Communication Module

1785-BCM

Allen Bradley 1785-BCM is a high speed backup communications module for the PLC-5 system of programmable logic controllers. The modules provides high speed backup communications and switchover of the Data Highway Plus and remote I/O links. The module is now obsolete and is no longer fully supported by Rockwell Automation. If you are using PLC-5/20, 5/30, 5/40 or 5/60 processors than you will need to purchase a BCM series B revision C or higher.

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.

1785-BCM module 1785-BEM module (when applicable) power supply local chassis

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.

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 Backup Concepts for the PLC-5 System Chapter 1 1-8 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 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 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.

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”. 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.

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