Technical data

Response to double
error
Once an error level has been activated (ADF, BCF, LZF, QVZ, REG,
ZYK) it cannot be activated again until it has been processed
completely, not even if a different program processing level is nested
within it. In this case, the PLC changes to the STOP mode
owing to the double call of a program processing level (DOPP in
the ISTACK).
Collisions of time interrupts are an exception, refer to the relevant
section). In the ISTACK, at depth "01", the DOPP identifier and the
error level called twice are marked.
Examples of double
call errors
Example 1:
During the processing of the ADF level (user
interface OB 25) a further processing error occurs.
Since the ADF level is still active, it cannot be
called a second time; the CPU changes to STOP.
STOP
Addressing error in PB 30
causes STOP
Addressing error in FB 5:
Call OB 25/
ADF level
CYCLE
ADF
FB 5
OB 1
PB 25
PB 26
PB 30
OB 25
Fig. 4-4 Change of level as a result of a double call error
4
Program Processing Levels
CPU 928B Programming Guide
C79000-B8576-C898-01
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