Technical data

Interrupt points Process interrupt-driven program execution can only be interrupted by
the following:
•• a program or device error (at operation boundaries)
•• operator intervention (PG function, stop switch, MP-STP),
•• the stop operation.
Note
Interrupt-driven program execution cannot be interrupted by
time-driven program execution or by a further process
interrupt
.
Multiple interrupts If further process interrupts occur during the interrupt-driven program
execution, these are
ignored until OB 2 has been completely
processed
(including all the blocks called in OB 2).
The CPU then returns to the point of interruption and executes the
program until the next block boundary. Only then is a new process
interrupt accepted and OB 2 called again. This means that a
permanently active interrupt cannot totally block cyclic program
execution. (This is not the case if you selected process interrupts at
operation boundaries in DX 0.)
Note
Multiple interrupts are not detected.
OB 2 can also be called when the signal state of the interrupt line
is passive again when the block boundary is reached.
Edge-triggered process interrupts occurring during the execution
of OB 2 and remaining active for a shorter time than OB 2 are not
detected (if level triggered).
The signal state of the interrupt signal between its becoming
active and the completion of OB 2 (BE operation) is irrelevant.
Process interrupt signal In the default (DX 0), the process interrupt signal for the CPU 928B is
level-triggered. i.e. the active state of the interrupt line sets a request
which causes OB 2 to be processed at the next block or operation
boundary (depending on the setting of DX 0).
RUN Mode
CPU 928B Programming Guide
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