Technical data

Diagnostics
23.9 Program Measures for Handling Errors
Programming with STEP 7
504 Manual, 05/2010, A5E02789666-01
Error OBs
A distinction is made between synchronous and asynchronous errors as follows:
• Synchronous errors can be assigned to an MC7 instruction (for example, load instruction for a
signal module which has been removed).
• Asynchronous errors can be assigned to a priority class or to the entire programmable logic
controller (for example, cycle time exceeded).
The following table shows what types of errors can occur. Refer to your "S7-300 Programmable
Controller, Hardware and Installation Manual" or the "S7-400, M7-400 Programmable Controllers,
Hardware and Installation Manual" for information as to whether your CPU provides the specified
OBs.
Error Class Error Type OB Priority
I/O redundancy error (only in H
CPUs)
OB 70 25 Redundancy
CPU redundancy error (only in H
CPUs)
OB 72 28
Time error OB 80 26
Power supply error OB 81 (or 28 if the error OB is called
Diagnostic Interrupt OB 82 in the startup program)
Insert/remove module interrupt OB 83
CPU hardware fault OB 84
Program sequence error OB 85
Rack failure OB 86
Asynchronous
Communication error OB 87
Programming error OB 121 Priority of the OB that caused the errorSynchronous
I/O access error OB 122