Siemens CPU 948 Programming Manual page 20

Which Operands are available to the User Program?
F flags
S flags (extended flag area)
1 - 12
Characteristics
The flag area is a memory area which the user
program can access extremely quickly with certain
operations.
The flag area should be used ideally for working data
required often.
The following data types can be accessed:
- single bits,
- bytes,
- words,
- double words.
Single flag bytes can be used as interprocessor
communication flags (IPC flags) to exchange data
between the CPUs in the multiprocessor mode (refer
to Chapter 10). IPC flags are updated by the system
program at the end of the cycle via a buffer in the
coordinator or CP/IP.
Characteristics
The CPU 948 also contains an additional flag area, the
S flag area. The user program can also access this area
extremely quickly as with the F flags.
S flags cannot however by used as actual operands
with function block calls nor as IPC flags for data
exchange between the CPUs. The bit test operations of
the CPU 948 can also not be used with the S flags.
These flags can only be used with the PG system
software "S5-DOS" from version 3.0 upwards or
"S5-DOS/MT" from version 1.0 upwards.
Size
2048 bits
Size
32 768 bits
CPU 948 Programming Guide
C79000-G8576-C848-04