Siemens CPU 948 User Manual

Collision of timed interrupts In the CPU 948 there are two different types of collisions of timed
interrupts:
Type of error/cause ISTACK ID Reaction of the CPU
Timed interrupt queue overflow:
- there are more than three
timed interrupts pending for one of
the three shortest time bases (OB 10
to 12),
- one of the other OBs (OB 13 to 18)
is called again before it has been
completely processed.
In the "ISTACK output" of
the programmer, the error ID
WEFES is marked in the
control bits.
The system program calls
OB 33 as the user interface.
If this is not loaded, the CPU
changes to the stop mode.
If the program can be interrupted at
block boundaries, the timed processing
is blocked by the run time of a block in
the cyclic user program; the run time of
the block is longer than the basic clock
rate set in DX 0.
In the "ISTACK output" on
the programmer, the error ID
WEFEH is marked in the
control bits.
The system program calls
OB 33 as the user interface.
If this is not loaded, the
system program continues
program execution.
Error reaction
OB 33
In OB 33, you can program the required reaction to the interrupt
collisions listed above. When OB 33 is called, the system program
enters a collision ID in ACCU-1-L (bit nos. 0 to 9). You can see the
meaning of these bits (bit = ’1’) in the following table.
Bit number Meaning
0
1
2
Queue overflow in timed interrupt period 1 (more than three timed interrupts are
pending for OB 10).
Queue overflow in timed interrupt period 2 (more than three timed interrupts are
pending for OB 11).
Queue overflow in timed interrupt period 3 (more than three timed interrupts are
pending for OB 12).
3
4
Queue overflow in timed interrupt period 4 (OB 13 has been called again before the
prior call was completely executed).
Queue overflow in timed interrupt period 5 (OB 14 has been called again before the
prior call was completely executed).
Table 4-6 Timed interrupt collision IDs: meaning of the bits in ACCU-1-L
RUN Mode
CPU 948 Programming Guide
C79000-G8576-C848-04
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Siemens CPU 948 Specifications

General

Brand	Siemens
Model	CPU 948
Category	Controller
Language	English