Technical data

SED/SEE disable/enable
semaphore
(non-system operations)
Operation Operand Function
SED
SEE
0 to 31
0 to 31
Disable (set) a semaphore
Enable (release) a semaphore
evaluation of the result of the operation via
CC 0/CC 1
Note
The SED xx and SEE xx operations must be programmed in all
CPUs
that require synchronized access to a common global
memory area.
Standard FBs, handling blocks and blocks for multiprocessor
communication manage the coordination internally. If you use
these blocks, you do not need to program the operations SEE xx
and SED xx.
Effect of SED/SEE The CPU that executes the operation SED xx (disable semaphore)
accesses a specific byte in the coordinator (
provided that no other
CPU has access to that byte already). Once a CPU has reserved
access, the other CPUs can no longer access the memory area
protected by the semaphore (numbers 0 to 31). The area is therefore
disabled for all other CPUs.
Make sure that the coordination functions correctly, all CPUs
requiring access to the same area of global memory must use the same
semaphore.
The SEE xx (enable semaphore) operation resets the byte on the
coordinator. The protected memory area is then once again accessible
to the other CPUs. A semaphore can only be enabled by the CPU that
disabled it.
Table 3-25 Disable/enable semaphore
Semaphore Operations
CPU 928B Programming Guide
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