GE PACSystems RSTi-EP, Cpu Programmer'S Reference Manual

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Chapter 3. Program Data
GFK-2950C February 2018 43
3.6 Retentiveness of Logic and Data
Data is defined as retentive if it is saved by the CPU when the CPU transitions from STOP Mode to
RUN Mode.
The following items are retentive:
▪ program logic
▪ fault tables and diagnostics
▪ checksums for program logic
▪ overrides and output forces
▪ word data (%R, %W, %L, %P, %AI, %AQ)
▪ bit data (%I, %G, fault locating references, and reserved bits)
▪ %Q and %M variables that are configured as retentive (%T data is non-retentive and therefore
not saved on STOP Mode to RUN Mode transitions).
▪ symbolic variables that have a data type other than BOOL
▪ symbolic variables of BOOL type that are configured as retentive
▪ Retentive data is also preserved during power-cycles of the CPU with battery backup or Energy
Pack backup. Exceptions to this rule include the fault locating references and most of the %S,
%SA, %SB, and %SC references. These references are initialized to zero at power-up regardless
of the state of the battery or Energy Pack. (For a description of the behavior of each, refer to
System Status References .)
When %Q or %M variables are configured as retentive, the contents are retained through power loss
and Run-to-Stop-to-Run transitions.