Siemens Simatic S7-1500 / ET 200MP - Page 209

Basics of program execution
9.1 Events and OBs
Automation system
208 System Manual, 01/2023, A5E03461182-AK
Event sources Possible priorities (default
priority)
Possible OB
numbers
Default system
reaction
1)
Number of OBs
Programming error (only for
global error handling)
2 to 26 (7)
121
STOP
0 or 1
I/O access error (only for
global error handling)
2 to 26 (7) 122 Ignore 0 or 1
1)
If you have not configured the OB.
2)
For these event sources, apart from the permanently assigned OB numbers (see column: possible OB numbers), you can
also assign OB numbers from the range ≥ 123 in STEP 7.
3)
If the maximum cycle time has been exceeded twice within a cycle, the CPU always switches to STOP regardless of
whether you have configured OB80.
4)
You will find more information on these event sources and the starting behavior in the S7-1500/S7-1500T Motion Con-
trol function manual.
Response to start events
The occurrence of a start event results in the following reaction:
• If the event comes from an event source to which you have assigned an OB, this event
triggers the execution of the assigned OB. The event enters the queue according to its
priority.
• If the event comes from an event source to which you have not assigned an OB, the CPU
executes the default system reaction.
Note
Some event sources, such as startup, pull/plug, exist even if you do not configure them.
Assignment between event source and OBs
The type of OB determines where you assign OB to event source:
• For hardware interrupts and isochronous mode interrupts: The assignment is made during
the configuration of the hardware or when the OB is created.
• For MC-servo, MC-PreServo, MC-PostServo, MC-Interpolator and MC-PreInterpolator:
automatic assignment of OBs 91/92 by STEP 7 as soon as you add a technology object.
• For all other OB types: Assignment when the OB is created, where applicable after you
have configured the event source.
For hardware interrupts, you can change an assignment which has already been made during
runtime with the instructions ATTACH and DETACH. In this case, only the actually effective
assignment changes, and not the configured assignment. The configured assignment takes
effect after loading, and upon each startup.
The CPU ignores hardware interrupts to which you did not assign an OB in your configuration
or which occur after the DETACH instruction. The CPU does not check whether an OB is
assigned to this event when an event arrives, but only prior to the actual processing of the
hardware interrupt.