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3-2 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide
–
May 2000 GFK-1527A
3
Program Folders in Logicmaster 90
With the Logicmaster programming software, there must be different folders for each
configuration. If the logic is identical for both PLCs, a third folder could be used for the logic and
reference tables. This results in three folders for the system.
Folder A - configuration for the Primary unit.
Folder B - configuration for the Secondary unit.
Folder C - logic and reference tables for both systems.
CPU Configuration Parameters
When configuring a system for Hot Standby CPU Redundancy, the following additional parameters
must be set up.
Parameter Default Choices Description / Comment
I/O Scan Stop Must be set to NO
Watchdog
Timer
200ms 10ms to
1000ms
The value selected should allow for the expected
scan
plus
two fail wait times.
Redund
Type
Primary
Primary,
Secondary
Whether the CPU being configured is the Primary or
Secondary CPU in the Redundancy system. One
configuration must be set to Primary; the other to
Secondary.
Background
Timer
5ms in limited
window mode
0ms to
255ms
The background window runs several diagnostic tests
that can be disabled by setting the timer to 0ms.
These tests are run in Constant Window and
Constant Sweep mode only if the window/sweep
time is large enough.
Fail-wait
60ms 60ms to
400ms
The time one PLC will wait on one Redundancy
Communications Module link for the other PLC to
respond before faulting that link. The CPU will try
both links before continuing its scan. Once the RCM
links are marked as failed, one unit or the other must
be power cycled to recover them.
Storing configuration to either unit could also
recover the RCM links.
Control
Strategy
GHS (CPU780)
GDB (CGR772,
CGR935)
GHS or
GDB
Genius Hot Standby (GHS) or
Genius Dual Bus (GDB).
Shared I/O
References
The references within the control of the Redundancy system. See the following
paragraphs for more information. The Shared I/O selections must match exactly
between Primary and Secondary PLCs.
Fault
Category
(configurable
when not
synchronized
only)
Fatal,
Diagnostic
Fault actions when the CPUs are not synchronized
can be configured to select a safe shutdown or fault
tolerant operation in case a failure occurs with no
backup ready.