Siemens SIMATIC S7-1500 System Manual page 168

Types of event sources
MC servo interrupt
MC interpolator interrupt
Programming error (only for
global error handling)
I/O access error (only for
global error handling)
* If OB was not configured
** For these event sources, besides the permanently assigned OB numbers (see column: possible OB numbers), you can
also assign OB numbers from the range ≥ 123 in STEP 7.
*** If the cycle monitoring time was exceed twice within a cycle, the CPU always switches to STOP, regardless of whether
OB80 was configured.
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
● STEP 7 automatically assigns OBs 91/92 to the MC-Servo interrupt and MC-Interpolator
● For all other types of OB, the assignment is made when the OB is created, where
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 is changed, not the configured assignment. The configured assignment
takes effect after loading, and upon each startup.
Hardware interrupts are ignored if no OB was assigned by their configuration or if they occur
after the DETACH instruction. The check as to whether an OB is assigned to an event does
not take place when the associated event occurs, but only when the hardware interrupt
actually has to be executed.
S7-1500 Automation System
System Manual, 02/2014, A5E03461182-AB
Possible priorities
(default priority)
17 to 26 (25)
16 to 26 (24)
2 to 26 (7)
2 to 26 (7)
during the configuration of the hardware or when the OB is created.
interrupt, as soon as an "S7-1500 Motion Control" technology object is added.
applicable after you have configured the event source.
Possible OB Default system
numbers reaction*
91 not applicable
92 not applicable
121 STOP
122 Ignore
Basics of program processing
14.1 Events and OBs
Number of OBs
0 or 1
0 or 1
0 or 1
0 or 1
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