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Program Execution Levels
Example of
"Interrupt stack":
ADF
SUF
CYCLE
Fig. 4-2
Principle of changing level and the ISTACK
Example of
"Interrupting a basic level with interruptability at block
boundaries":
A timed interrupt occurs while a process interrupt is being serviced.
Since the timed interrupt has a higher priority, the servicing of the
PROCESS INTERRUPT is interrupted at the next block boundary and the
TIMED INTERRUPT level nested in. If an addressing error now occurs
while servicing the timed interrrupt, the timed interrupt servicing is
interrupted immediately at the next operation boundary to nest in the
ADF level.
4 - 8
Stop switch
STOP
ADF
SUF
CYCLE
ISTACK =
WARM RESTART
Depth 1
Depth 2
Depth 3
Depth 4
Image of the
interrupted levels
ADF
SUF
START-UP
CYCLE
CPU 948 Programming Guide
C79000-G8576-C848-04
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