Technical data

5.7.3
Example of Error Diagnosis
using the ISTACK
Example 1:
Fig. 5-3 illustrates the structure of the ISTACK in conjunction with the
interruptions that have occurred.
- Die Programmbearbeitungsebene ZYKLUS (
OB 1) wird unterbrochen durch
das Auftreten eines Interrupts.
- Following this, the program processing level TIME INTERRUPT is
activated and
OB 13 is processed.
- The TIME INTERRUPT level is exited owing to the occurrence of a process
interrupt, the PROCESS INTERRUPT level is activated and
OB 2 is
processed.
- An incorrect addressing operation activates level ADF where
OB 25 is
processed. In the error handling program, the user has programmed a
stop operation (STP); the CPU aborts program execution.
Before the CPU finally goes into the stop mode, a total of four
different program processing levels have been interrupted. If you
display the ISTACK, you obtain a
four level ISTACK, first the ISTACK
with depth 01, in which the identifier of the program processing level
last interrupted (=ADF) is marked. You can now "page down" through the
ISTACK until you reach the ISTACK with depth 04, that represents the
CYCLE program processing level, that was interrupted
first.
OB13
Depth 01
OB2
OB1
CYCLE
ADF
OB25
Program processing levels ISTACK
Level: 003C
Depth 02
Level: 0024
ADF
x
Depth 03
Level: 0010
Depth 04
Level: 0004
STP
STP
x
TIME
INTERRUPT
INTERRUPT
PROCESS
Fig. 5-3 Example 1 of evaluating the ISTACK
5
Control Bits and Interrupt Stack
CPU 928B Programming Guide
C79000-B8576-C898-01
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