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11GFK-0827 Chapter 1 Introduction
The Primary Unit and the Secondary Unit must be configured separately. That is, the
programming device should be connected directly to either the Primary or the
Secondary Unit to configure that unit. When you have completed configuring that unit,
disconnect the programmer from the configured unit and move it to the other unit and
proceed with configuration of the second unit. Refer to Chapter 3, ”System
Configuration” for details of configuring a Redundancy system
Definition of Terms
Several new or unfamiliar terms are used throughout this manual which are relevant to
the discussions of CPU Redundancy. These terms are defined in the following table.
Term Definition
Active Unit The unit that is actively controlling the process.
Backup Unit That unit that is synchronized with the active unit and able to take over the process.
CPU Redundancy A system with two PLC CPU units cooperating to control the same process.
Critical Component A component whose failure causes the PLC (either active or backup) in which it resides to
stop.
Hot Standby A feature of Genius blocks whereby the block prefers output data from the
Bus Controller at Serial Bus Address 31. When inputs from that Bus Controller are not
available, the block takes output data from the Bus Controller at Serial Bus Address 30.
If inputs from neither Controller are available, the block places its outputs in the
designated default state.
Local Unit The RCM LEDs and %S status bits refer to the PLC in which they reside as
the ”Local Unit”.
Primary Unit The unit in which the Genius Bus Controller’s Serial Bus Address is 31.
Redundancy A system feature that has multiple elements controlling the same process to provide alter-
nate functional channels in case of failure.
Remote Unit The RCM LEDs and status bits refer to the other PLC as the ”Remote Unit”.
For example, the Primary Unit is the Remote Unit to the Secondary Unit and likewise
the Secondary Unit is the Remote Unit to the Primary Unit.
Secondary Unit The unit in which the Genius Bus Controller’s Serial Bus Address is 30.
Synchronized A unit is considered to be synchronized when it has received the latest status information
from the Active unit and is running the PLC program in parallel.