Before disabling or enabling a particular semaphore, the SED and SEE
operations scan the status of the semaphore. The condition codes CC 0
and CC 1 are affected as follows:
CC 1 CC 0 Evaluation Significance
0 0 JZ Semaphore was disabled by
another CPU and cannot be
disabled/enabled.
1 0 JN, JP Semaphore was disabled/
enabled.
Note
The scanning of a particular semaphore (= read procedure) and
the disabling or enabling of the semaphore (=write procedure) are
one unit. No other CPU can access the semaphore during these
procedures!
When using semaphores, remember the following points:
•• A semaphore is a global variable, i.e. the semaphore with number
16 exists only once in the entire system, even if your controller is
using three CPUs.
•• All CPUs that require coordinated access to a common memory area
must use the SED and SEE operations.
•• All participating CPUs must execute the same start-up type. Du-
ring a COLD RESTART, all the semaphores are cleared. During a
manual or automatic warm restart, the semaphores are retained.
•• Start-up in multiprocessor operation must be synchronized. For
this reason, no test operation is allowed.
Semaphore Operations
CPU 948 Programming Guide
C79000-G8576-C848-04
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