Special feature with cyclic
functions on both PGs
If the interrupting function blocks the CPU 948 ("status" in a block
that is not executed) the interrupted function is also blocked. It can
only be resumed when the interrupting function is terminated.
When working simultaneously with two PGs, the following sequence
results:
PG 1 informs the CPU
of the variables
to be output.
PG 1 requests the
current data.
(PG signals: status
processing active)
PG 1 requests the
current data.
PG 1 requests the
current data.
PG 1 must wait until
the CPU is free.
PG 2 must wait until
the CPU is free.
Job sent by PG 2 is processed
(PG signals: status processing active
(PG signals: statement
not processed)
PG2 sends a new job
(e.g. "Status PB 9").
PG 2 job complete
PG 1 receives new data
PG 2 aborts the STATUS function;
The CPU processes the abort reque
CPU 948
User on PG 1 User on PG 2
Fig. 11-9 Sequence when a function blocks the CPU 948
Parallel Operation of Two Serial PG Interfaces
CPU 948 Programming Guide
C79000-G8576-C848-04
11 - 25
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