Technical data

Interrupt points Time-driven program execution can be interrupted either at block
boundaries
(default) or at operation boundaries (programmed in
DX 0) by the following:
•• processing of a process interrupt
•• processing of a delay interrupt
•• processing of a closed loop controller interrupt
•• renewed processing of a time interrupt
Processing can be interrupted at operation boundaries or aborted
completely by the following:
•• the occurrence of a hardware fault or program error
•• operator intervention (PG function, stop switch, MP-STP)
•• the stop operation STP.
Note
Time-driven program execution cannot be interrupted by the
same time interrupt (collision of time interrupts).
Collision of time interrupts
(WECK-FE)
If a time interrupt OB has not yet been completely processed and is
called a second time, a collision occurs. A time interrupt collision also
occurs if an OB is called a second time and the first call has not been
processed. This is possible when the time interrupts can only interrupt
the cyclic program at block limits, particularly if your STEP 5
program contains blocks with long runtimes.
If a collision of time interrupts occurs, the error program processing
level WECK-FE is activated and the system program calls
OB 33 as
the user interface. In OB 33, you can program a specific reaction to
this problem.
If OB 33 is not loaded, the CPU goes into Stop if an error occurs.
Then WECK-FE is indicated on the programmer in the control bits
"Output ISTACK" screen. The level ID of the relevant time interrupt
(LEVEL) is indicated in the ISTACK.
RUN Mode
CPU 928B Programming Guide
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