Bit Memory References; Transition Bits And Override Bits - GE VersaMax PLC User Manual

Normally used for discrete inputs, and viewable in the Input Status Table.
%I
Normally used for physical output references, and viewable in the Output Status Table. A %Q
%Q
reference may be either retentive or non-retentive, depending on its use in the program.
Normally used to represent internal references. A specific %M reference may be either retentive
%M
or non-retentive, depending on its use in the program.
Used for temporary references that can be used many times in a program. Data with %T
%T
references is not retained through loss of power or RUN-TO-STOP-TO-RUN transitions. %T
references cannot be used with retentive coils.
System status references, which have specific predefinitions.
n %S, %SA, %SB, and %SC can be used for any type of logic contact.
%S n %SA, %SB, and %SC can be used for retentive coils.
n %S can be used as inputs to functions or function blocks.
n %SA, %SB, and %SC can be used as inputs or outputs of functions and function blocks.
Used for Global Data. Data in %G references is retained through power loss. %G references can
%G
be used with contacts and retentive coils, but not on non-retentive coils.
Program Data
For public disclosure

9.1.2 Bit Memory References

Each bit memory address (reference) is on a bit boundary. Data is stored in bit memory as
represented below. The illustration shows 160 individually-addressed bits, with address 1
in the upper left and address 160 in the lower right.
addresses
1 2 3 4 5 6 7
0 0 1 1 0 0 0
0 0 1 1 0 0 0
1 1 1 1 0 0 0
1 1 0 0 0 0 0
0 1 0 1 0 0 0
1 1 0 0 0 0 0
1 1 0 1 0 0 0
1 1 0 0 0 0 0
1 0 0 1 0 0 0
0 0 0 1 0 0 0
The PLC uses six types of references for data stored in bit memory.

9.1.3 Transition Bits and Override Bits

%I, %Q, %M, and %G references have associated transition and override bits.
%T, %S, %SA, %SB, and %SC references have associated transition bits only.
The CPU uses transition bits for transitional coils. When override bits are set, the
associated references can only be changed from the programmer.
8
0 0 0 0 0 1 0 0 0
0 0 0 1 0 1 0 0 0
1 1 0 0 1 0 0 0 0
1 1 1 0 0 1 0 1 0
1 0 1 0 1 0 0 0 0
1 1 1 0 0 1 0 1 0
1 1 1 0 1 0 0 0 0
1 1 0 1 1 1 0 1 1
1 1 0 1 1 1 0 0 1
0 1 0 1 0 1 0 0 1
... 160
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