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GFK-1527A Chapter 1 Introduction 1-5
1
Components of the Enhanced Hot Standby Redundancy System
Enhanced Redundancy CPU Module
To utilize the features described in this manual, an Enhanced Redundancy CPU Module
(IC697CGR935 or IC697CGR772) must be installed rack 0, slot 1 of both the Primary and
Secondary PLCs. Features of the redundancy CPU that are different from conventional CPUS are
listed on the previous page.
Redundancy Communications Module
Two Redundancy Communications Modules (RCM) are available that provide a path for sharing
data between the two CPUs in the redundant system. Catalog number IC697RCM711 is for use in
standard Series 90-70 racks and IC687RCM711, which is for use in dual redundant racks
(described below).
The RCM module has a pushbutton switch that can be used to manually switch control from the
active unit to the backup unit. The switch between units can also be controlled through the
application program logic.
In a synchronized system, I/O data is controlled by only one unit (the active unit) but is shared
between both units (active and backup units). The Redundancy Communications Module provides
a communications path to synchronize the two CPUs. It also provides the communications path for
the transfer of I/O data. An RCM must be located in the main rack of both the Primary PLC and
the Secondary PLC, or in both sections of a dual redundant rack.
Redundant Racks
Redundant racks; IC697CHS770 (rear mount) and IC697CHS771 (front mount) have two power
supply slots and 12 backplane slots divided into two separate sections, each having a power supply
slot and 6 backplane slots. The redundant rack is designed for easy integration of third-party VME
modules into a Series 90-70 PLC system. These racks accept all standard Series 90-70 modules
and ½ slot VME modules. VME modules require 0.8” spacing and use one slot, while standard
Series 90-70 modules use two of the available slots. Cable connection between the required ½ slot
RCM modules and the required ½ slot BTM modules (catalog number IC687BEM713) in a
redundant rack is through an available 3 foot (0.9 meter) cable, IC697CBL803.
I/O Systems for Enhanced Hot Standby CPU Redundancy
Both Series 90-70 Local I/O and Genius I/O systems can be present in an Enhanced Hot Standby
CPU Redundancy system. The two PLCs need not have matching I/O systems -- they may have
different numbers of I/O racks, different I/O modules and different option modules.