Siemens S7-1200 System Manual page 95
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- Operating instructions manual (132 pages) ,
- Programming manualline (74 pages) ,
- Manual (46 pages)
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Interruptible and non-interruptible execution modes
OBs (Page 85) execute in priority order of the events that trigger them. With V4.0 of the S7-
1200 CPU, you can configure OB execution to be interruptible or non-interruptible. Note that
program cycle OBs are always interruptible, but you can configure all other OBs to be either
interruptible or non-interruptible.
If you set interruptible mode, then if an OB is executing and a higher priority event occurs
before the OB completes its execution, the running OB is interrupted to allow the higher-
priority event OB to run. The higher-priority event runs, and at its completion, the OB that
was interrupted continues. When multiple events occur while an interruptible OB is
executing, the CPU processes those events in priority order.
If you do not set interruptible mode, then an OB runs to completion when triggered
regardless of any other events that trigger during the time that it is running.
Consider the following two cases where interrupt events trigger a cyclic OB and a time delay
OB. In both cases, the time delay OB (OB201) has no process image partition assignment
(Page 77) and executes at priority 4. The cyclic OB (OB200) has a process image partition
assignment of PIP1 and executes at priority 2. The following illustrations show the difference
in execution between non-interruptible and interruptible execution modes:
Figure 4-1
Figure 4-2
Note
If you configure the OB execution mode to be non-interruptible, then a time error OB cannot
interrupt OBs other than program cycle OBs. Prior to V4.0 of the S7-1200 CPU, a time error
OB could interrupt any executing OB. With V4.0, you must configure OB execution to be
interruptible if you want a time error OB (or any other higher priority OB) to be able to
interrupt executing OBs that are not program cycle OBs.
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
Case 1: Non-interruptible OB execution
Case 2: Interruptible OB execution
PLC concepts
4.1 Execution of the user program
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