Siemens SIMATIC S7-400H - Monitoring Functions of the CPU

Assembly of a CPU 41x–H
5.2 Monitoring functions of the CPU
S7-400H
52 System Manual, 03/2012, A5E00267695-11
5.2 Monitoring functions of the CPU
Monitoring functions and error messages
The hardware of the CPU and operating system provide monitoring functions to ensure
proper operation and defined reactions to errors. Various errors may also trigger a reaction
in the user program.
The table below provides an overview of possible errors and their causes, and the
corresponding responses of the CPU.
Additional test and information functions are available in each CPU; they can be initiated in
STEP 7.
Type of error Cause of error Response of the operating system Error LED
Access error Module failure (SM, FM, CP) LED "EXTF" remains lit until the error
is eliminated.
In SMs:
 Call of OB 122 with direct access,
call of OB 85 in the event of a
process image update
 Entry in the diagnostic buffer
 In the case of input modules: Entry
of "null" as date in the accumulator
or the process image
In the case of other modules:
 Call of OB 122 with direct access,
call of OB 85 in the event of a
process image update
EXTF
Time error
 The user program execution time (OB 1
and all interrupts and error OBs)
exceeds the specified maximum cycle
time.
 OB request error
 Overflow of the start information buffer
 Time-of-day error interrupt
LED "INTF" remains lit until the error is
eliminated.
Call of OB 80.
If the OB is not loaded: CPU changes
to STOP mode.
INTF
Power supply
module(s) fault
(not power failure)
In the central or expansion rack:
 at least one backup battery in the power
supply module is flat.
 the backup voltage is missing.
 the 24 V supply to the power supply
module has failed.
Call of OB 81
If the OB is not loaded: The CPU
remains in RUN.
EXTF