EDIT: I am feeling bad today so may not have read the question thoroughly. My answer relevant 90-30, 90-70 and VersaMax ladder logic...I am not sure what the F is refering too. I havent worked with GE for awhile so hopefully Steve or Russ will clarify the issue and any mistakes I have made.
Discrete
%I The %I prefix represents input references. %I references are located in the input status table, which stores the state of all inputs received from input modules during the last input scan. %I memory is always retentive.
%Q The %Q prefix represents physical output references. %Q references are located in the output status table, which stores the state of the output references as last set by the application program. This output status table's values are sent to output modules at the end of the program scan. A particular %Q reference may be either retentive or nonretentive, depending on its use in the program.
%M The %M prefix represents internal references. A particular %M reference may be either retentive or nonretentive.
%T The %T prefix represents temporary references that are used many times in a program. Data with %T references is not retained through power loss or Run-to-Stop-to-Run transitions. %T references cannot be used with retentive coils.
%S The %S, %SA, %SB, and %SC prefixes represent system status references. These references are used to access special PLC data such as timers, scan information, and fault information. For example, the %SC0012 bit can be used to check the status of the PLC fault table. Once the bit is set on by an error, it will not be reset until after the sweep.
%S, %SA, %SB, and %SC can be used on any type of logic contact.
%SA, %SB, and %SC can be used on retentive coils (M)
%S can be used as inputs to functions or function blocks.
%SA, %SB, and %SC can be used as inputs or outputs to functions and function blocks. %S, %SA, %SB, and %SC references are nonretentive.
%G The %G, %GA, %GB, %GC, %GD, and %GE prefixes represent global data references. These references are used to access data shared among several PLCs. %G, %GA, %GB, %GC, %GD, and %GE references can be used on contacts and retentive coils, but not on nonretentive coils
Register
%R Use the prefix %R to assign system register references, which will store program data such as the results of calculations.
%AI The prefix %AI represents an analog input register. This prefix is followed by the register address of the reference (for example, %AI0015). An analog input register holds the value of one analog input or another value.
%AQ The prefix %AQ represents an analog output register. This prefix is followed by the register address of the reference (for example, %AQ0056). An analog output register holds the value of one analog output or other non-discrete value.
%P (Series 90-70 only) Use the prefix %P to assign program register references that will store program data from the _MAIN block. This data can be accessed from all program blocks. The size of the %P data block is based on the highest %P reference in all blocks. This reference type is scoped at a program level and is therefore only visible to LD programs.
%L (Series 90-70 only) Use the prefix %L to assign local register references that will store program data unique to a block. The size of the %L data block is based on the highest %L reference in the associated block. This reference type is scoped at a program level and is therefore only visible to LD programs.
Note: All register references are retained across a power cycle to the CPU. In 90-70 PLCs, you can use indirect referencing for all register references (%R, %AI, %AQ, %P, and %L) to identify a location in memory that contains the offset in the same memory type of the data to be used.
