Omron CS1D DUPLEX SYSTEM - 10-2009 Operation Manual page 151

Duplex CPU Units
Active and Standby
CPU Units
Active and Standby CPU
Unit Operations
In Duplex Mode, the two CPU Units run the same user program. One of them
executes actual control (e.g., refreshing the other Units), and the other one
remains on standby as a backup.
The two CPU Units use synchronized processing and the same user program,
I/O memory, and Parameter Area data.
Active CPU Unit The active CPU Unit is the main CPU Unit that executes con-
trol. It runs the user program and exchanges data with exter-
nal devices (through mounted Units and communications).
Standby CPU Unit The standby CPU Unit runs the user program in parallel with
the active CPU Unit, and remains on standby to switch to
active status in case the active CPU Unit goes down. It con-
stantly receives updated data from the active CPU Unit.
• The setting at the Active Setting Switch on the Duplex Unit determines
which of the two CPU Units is to be active.
• The R and L ACTIVE indicators on the Duplex Unit show which of the two
CPU Units is active. The active/standby status can also be checked using
A32809 in the Auxiliary Area.
When the user program or parameters (e.g., PLC Setup) are changed, they
are transferred from the active CPU Unit to the standby CPU Unit. I/O memory
is transferred with each cycle. (These transfers are called "duplex transfers.")
The details of active and standby CPU Unit operations are described below.
Data Transfers
Data
User program Transferred from active to standby CPU Unit whenever changed.
I/O memory Constantly transferred from active to standby CPU Unit.
Parameters Transferred from active to standby CPU Unit whenever changed.
CPU Unit
Active CPU Unit
Section 3-1
Standby CPU Unit
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