User Program Memory Usage; L And %P Program Memory; Program Logic And Overhead - GE PACSystems RXi User Manual

Appendix C. User Memory Allocation

User Program Memory Usage

C.2
Space required for user logic includes the following items.
C.2.1

%L and %P Program Memory

%L and %P are charged against your user space and sized depending on their use in your
applications. The maximum size of %L or %P is 8192 words per block.
The %L and %P tables are sized to allow extra space for Run Mode Stores according to the
following rules.
C.2.2

Program Logic and Overhead

The data area for C (.gefelf) blocks is considered part of the user program and counts against
the user program size. Additional space is required for information internal to the CPU that is
used for execution of the C block.
The program block is based on overhead for the block itself plus the logic and register data
being used (that is, %L).
308
■
If %L memory is not used in the block, the %L memory size is 0 bytes. If %L memory
is used in the block, a buffer is added beyond the highest %L address actually used
in logic or in the variable table. The default buffer size is 256 bytes, but can be
changed by editing the Extra Local Words parameter in the block Properties.
■
The same rules apply for the size of %P memory, but %P memory can be used in
any block in the program.
■
The buffer cannot make the %P or %L table exceed the maximum size of 8,192
words. In such a case, a smaller buffer is used.
■
You can add, change, or delete %L and/or %P variables in your application and Run
Mode Store the application if these variables fit in the size of the last-stored %L/%P
tables (where the size includes the previous buffer space), or if going from a zero to
non-zero size.
■
The size of the %L/%P tables is always recalculated for Stop Mode Stores.
The LD program's stack is not counted against the CPU's memory size.
Note:
Note: If your application needs more space for LD logic, consider changing some
%P or %L references to %R, %W, %AI, or %AQ. Such changes require a
recompilation of the program block and a Stop Mode store to the CPU.
PACSystems* RXi Distributed IO Controller User Manual GFK-2816F