Siemens S7-1200 System Manual page 90

PLC concepts
4.1 Execution of the user program
Diagnostic error events
Analog (local), PROFINET, PROFIBUS, and some digital (local) devices are capable of
detecting and reporting diagnostic errors. The occurrence or removal of any of several
different diagnostic error conditions results in a diagnostic error event. The following
diagnostic errors are supported:
● No user power
● High limit exceeded
● Low limit exceeded
● Wire break
● Short circuit
Diagnostic error events trigger the execution of the diagnostic error interrupt OB (OB 82) if it
exists. If it does not exist, then the CPU ignores the error.
To include a diagnostic error interrupt OB in your project, you must add a diagnostic error
interrupt by double-clicking "Add new block" under "Program blocks" in the tree, then choose
"Organization block", and then "Diagnostic error interrupt".
Note
Diagnostic errors for multi-channel local analog devices (I/O, RTD, and Thermocouple)
The diagnostic error interrupt OB can report only one channel's diagnostic error at a time.
If two channels of a multi-channel device have an error, then the second error only triggers
the diagnostic error interrupt OB under the following conditions: the first channel error clears,
the execution of the diagnostic error interrupt OB that the first error triggered is complete,
and the second error still exists.
The diagnostic error interrupt OB includes startup information that helps you determine
whether the event is due to the occurrence or removal of an error, and the device and
channel which reported the error. You can program instructions inside the diagnostic error
interrupt OB to examine these startup values and to take appropriate action.
Note
Diagnostic error OB Start information references the submodule as a whole if no diagnostics
event is pending
In V3.0, the start information for an outgoing diagnostic error event always indicated the
source of the event. In V4.0, if the outgoing event leaves the submodule with no pending
diagnostics, the start information references the submodule as a whole (16#8000) even if the
source of the event was a specific channel.
For example, if a wire break triggers a diagnostic error event on channel 2, the fault is then
corrected, and the diagnostic error event is cleared, the Start information will not reference
channel 2, but the submodule (16#8000).
90
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG