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10 Series 90-70 Hot Standby CPU Redundancy User’s Guide – December 1993
GFK-0827
Programming Considerations
There are several features in the operation of the Redundancy CPU which are not
supported or are different then operation of other CPUs. These features are listed below
and are described in detail in Chapter 4, ”System Operation”.
The following features are not available with the Redundancy CPU (CPU 780):
I/O Interr upts
Timed Interrupts
VME Integrator Rack
STOP/IOSCAN mode
Flash memory operation
The operation of the following features is different with the CPU 780 than with other
Series 90-70 CPUs:
RUN/DISABLED mode
Configuration of fault actions
STOP to RUN mode
Default Background Window Time
Configuration Requirements
The Redundancy CPU and the Redundancy Communications Module must be
configured into the redundancy system. There are several additional parameters (other
than the normal CPU parameters) that must be configured with the Logicmaster 90-70
Configurator function which are unique to the Hot Standby CPU Redundancy system.
The following items require configuration when specifying the CPU 780 (the
Redundancy CPU) as the CPU for configuration:
Configuration
Parameter Description
Fail-wait (60 ms to 400 ms) The time to wait on a failed active PLC before switching to
the backup CPU. The default value is 60 ms.
Control Strategy The control strategy for the current configuration. Config-
ured as a three-character identifier (GHS for Hot Standby
CPU Redundancy). The default value is GHS (currently
the only value that is valid).
Shared I/O References The references within the control of the Redundancy sys-
tem; up to 20 KBytes of Input data and 28 KBytes of Out-
put data is transferred. The references which may be used
as shared I/O are %I, %Q, %AI, %AQ, %R, and %M.
Redund Type Whether the CPU being configured is the Primary or Sec-
ondary CPU in the Redundancy system. Redund Type
has three possible values: PRIMARY, SECONDARY, or
SIMPLEX. SIMPLEX (not supported in this release of the
product) indicates a non–redundant system. The default
value is PRIMARY.