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Causes of Error and Reactions of the CPU
5.6.9
OB 33: Collision of Timed
Interrupts Error
(WEFES/WEFEH)
Queue overflow
Masking the timed interrupt
clock
5 - 30
Time-controlled program processing (timed interrupts) is handled by
organization blocks OB 6, OB 9 and OB 10 to OB 18.
The following types of timed errors can occur on the CPU 948:
Cause:
Queue overflow servicing timed interrupts:
• • there are more than three timed interrupts pending for one of the
three shortest periods (OBs 10 to 12)
or
• • one of the other OBs (OBs 13 to 18) has been called before the
first call was completely processed.
Reaction:
The system program calls OB 33 as the user interface, if this is loaded.
You can program the reaction to this state in this OB.
If OB 33 is not loaded, the CPU changes to the STOP mode.
PG display in "OUTPUT ISTACK":
The bit WEFES is marked in the control bits.
Cause:
The internal timed interrupt clock is masked (ignored) too long
(applies to interruptions at block boundaries/process interrupts).
This situation is related to the basic clock rate of the internal timed
interrupts and the scan time of a block in the cyclic user program. If
the scan of a cyclic block runs longer than the basic clock rate, a
collision of timed interrupts occurs.
CPU 948 Programming Guide
C79000-G8576-C848-04
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