Siemens SIMATIC S7-1500 System Manual page 221

Event sources
Time error
Maximum cycle time exceeded
Diagnostics interrupt
Removal/insertion of modules 2 to 26 (6)
Rack error
Programming error (only for
global error handling)
I/O access error (only for global
error handling)
If you have not configured the OB.
1)
2) See section "Response of S7-1500R/H redundant system when cycle time is exceeded"
Response to start events
The occurrence of a trigger results in the following response:
• 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 (exception: hardware interrupts).
• 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.
Response of OB 72 and OB 86 to system state transitions
If an IO device has failed, the OB 86 reports a "rack failure" if programmed. OB 72 "CPU
redundancy error" reports a loss of redundancy in the redundant system or failure of the
redundant synchronization.
S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD
Possible priorities (default
priority)
22
2 to 26 (5)
2 to 26 (6)
2 to 26 (7)
2 to 26 (7)
Possible OB num­ Default system
bers response
80 Ignore
Depends on system
2)
state
82 Ignore
83 Ignore
86 Ignore
121 STOP
122 Ignore
Basics of program execution
9.3 Events and OBs
Number of OBs
1)
0 or 1
0 or 1
0 or 1
0 or 1
0 or 1
0 or 1
221