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GFK-1527A Chapter 4 Normal Operation 4-5
4
portion of the bus between the BSM and the blocks) result in loss of the blocks downstream from
the failure on that bus stub.
Bus failures in single bus networks result in loss of the blocks downstream from the bus failure.
When using the GDB control strategy, the user is required to transfer all redundant Genius outputs
to the backup unit so that both units drive the same output values.
%S References for CPU Redundancy
%S33 through %S39 and %SB18 reflect the status of the Redundancy units. The table below
describes these %S references, and shows their expected states in the Primary and Secondary Units,
assuming Primary is active and Secondary is backup.
Expected State
%S Bit Definition Nickname Description
Primary
Unit
Secondary
Unit
%S33 Primary Unit PRI_UNT Set if the local unit is configured as the primary unit:
otherwise; it is cleared. For any given local unit, if
PRI_UNT is set, then SEC_UNT cannot be set.
ON OFF
%S34 Secondary Unit SEC_UNT Set if the local unit is configured as the secondary unit:
otherwise; it is cleared. For any given local unit, if
SEC_UNT is set, then PRI_UNT cannot be set.
OFF ON
%S35 Local System
Ready
LOC_RDY Set if local unit is ready to become the active unit;
otherwise it is cleared.
ON ON
%S36
Local System
Active
LOC_ACT
Set if local unit is currently the active unit; otherwise it is
cleared. For any given local unit, if LOC_ACT is set, then
REM_ACT cannot be set.
ON
OFF (1)
OFF
ON (1)
%S37 Remote System
Ready
REM_RDY Set if remote unit is ready to become the active unit;
otherwise it is cleared.
ON ON
%S38 Remote System
Active
REM_ACT Set if remote unit is currently the active unit; otherwise it is
cleared. For any given local unit, if REM_ACT is set, then
LOC_ACT cannot be set.
OFF
ON (1)
ON
OFF (1)
%S39 Logic Equal LOGICEQ
(LOGIC=)
Set if the logic program for both units in the redundant
system is the same; otherwise the bit is cleared.
ON ON
%SB18 Redundant
Informational
Message, Fault
Logged
RDN_MSG Set if a redundant informational message was logged. It can be cleared in reference tables,
logic, or by clearing the fault tables.
(1) Condition if secondary is active unit.
%S references can be read from the application program, but cannot be altered or overridden.
These references are always OFF when no configuration has been stored. Once you have
completed configuration of the Redundancy system and STORED the configuration, the state of
these %S references is set and is maintained in STOP or RUN mode.
References %S35, %S36, %S37, and %S38 correspond to LEDs on the Redundancy
Communications Module. External indicators can also be used to monitor the status of %S35
through %S38 (Local Ready/Active, Remote Ready/Active) through the application program logic.
OVR_PRE %S Reference Not Available
The OVR_PRE %S reference which indicates whether one or more overrides is active
is not
supported by the Redundancy CPU and should not be used.