Siemens SIMATIC S7-1500 System Manual page 226

Basics of program execution
10.2 Events and OBs
Types of event sources
Programming error (only for
global error handling)
I/O access error (only for
global error handling)
If you have not configured the OB.
1)
For these event sources, apart from the permanently assigned OB numbers (see column: possible OB numbers), you can
2)
also assign OB numbers from the range ≥ 123 in STEP 7.
If the maximum cycle time has been exceeded twice within a cycle, the CPU always switches to STOP regardless of
3)
whether you have configured OB80.
You can find more information on these event sources and the startup behavior in the S7-1500 Motion Control function
4)
manuals.
Assignment between event source and OBs
The type of OB determines where you make the assignment between OB and event source:
• With 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,
STEP 7 automatically assigns OBs 91/92 as soon as you add a technology object.
• For all other types of OB, the assignment is made 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.
224
Possible priorities
(default priority)
2 to 26 (7)
2 to 26 (7)
Possible OB Default system
numbers reaction
121 STOP
122 Ignore
System Manual, 11/2023, A5E46600094-AD
Number of OBs
1)
0 or 1
0 or 1
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