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11.2 PG Functions
Calling and using functions
Checkpoint
CPU 948 Programming Guide
C79000-G8576-C848-04
Note
The terms used in this section for the PG functions may in some
cases differ from the terms in your PG software. Please refer to
your STEP 5 manual.
How to call and use the individual PG functions is described in the
manual for your PG.
The PG functions are performed at defined checkpoints in the CPU.
In the CPU 948 there are four different checkpoints. Each of these
checkpoints has certain test functions assigned to it.
Checkpoint "Stop"
You can access PG functions that are permissible only in the STOP
mode at checkpoint "stop" (e.g. "start", "overall reset", "compress
memory" in the stop mode).
The "stop" checkpoint is located immediately before OB 39 is called
(the block for cyclic processing in the soft STOP mode).
Checkpoint "Cycle"
PG functions that you want to execute during cyclic program
processing are called at checkpoint "cycle" (e.g. "compress memory"
in the RUN mode, "stop", "status"). The "cycle" checkpoint is located
immediately before the updating of the process image of the inputs
(PII). At this point, the system program has not updated the PII yet.
Checkpoint "Test"
PG functions that you want to execute as soon as the next breakpoint
is reached are called at checkpoint "test" (in the program test), see
Section 11.2.3).
Checkpoint "General Functions"
This checkpoint exists both in the STOP and the RUN mode. Online
PG functions that can be executed in all operating modes of the
programmable controller are called at checkpoint "general functions".
These functions include "transfer block", "delete block", "status
variables". In the STOP mode, this checkpoint is located immediately
before OB 39 is called (the block for cyclic processing in the soft
STOP mode). During cyclic program processing, the checkpoint is
located after updating the process image of the inputs and before
calling OB 1.
PG Functions
11 - 5
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