User Manual
Chapter 9
GFK-1503F
Jan 2020
Program Data
92
The PLC uses six types of references for data stored in bit memory.
%I
Normally used for discrete inputs, and viewable in the Input Status Table.
%Q
Normally used for physical output references, and viewable in the Output Status Table. A
%Q reference may be either retentive or non-retentive, depending on its use in the
program.
%M
Normally used to represent internal references. A specific %M reference may be either
retentive or non-retentive, depending on its use in the program.
%T
Used for temporary references that can be used many times in a program. Data with %T
references is not retained through loss of power or RUN-TO-STOP-TO-RUN transitions. %T
references cannot be used with retentive coils.
%S
System status references, which have specific predefinitions.
—
%S, %SA, %SB, and %SC can be used for any type of logic contact.
—
%SA, %SB, and %SC can be used for retentive coils.
—
%S can be used as inputs to functions or function blocks.
—
%SA, %SB, and %SC can be used as inputs or outputs of functions and function blocks.
%G
Used for Global Data. Data in %G references is retained through power loss. %G references
can be used with contacts and retentive coils, but not on non-retentive coils.
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.
9.2
Retentiveness of Data
Data is retentive if it is automatically saved when the PLC is stopped, or power cycled. The
following data is retentive:
•
Program logic
•
Fault tables and diagnostics
•
Overrides
•
Word data (%R, %AI, %AQ)
•
Bit data (%I, %SC, %G, fault bits and reserved bits)
•
Word data stored in %Q and %M
•
Data in %Q or %M references that are used as function block outputs or with retentive
coils:
—
-(M)- retentive coils
—
-(/M)- negated retentive coils
—
-(SM)- retentive SET coils
—
-(RM)- retentive RESET coils
