Monitoring Functions Of The Cpu - Siemens SIMATIC S7-400H System Manual

Assembly of a CPU 41x–H

5.2 Monitoring functions of the CPU

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
Access error Module failure (SM, FM, CP)
Time error




Power supply In the central or expansion rack:
module(s) fault

(not power failure)


52
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
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.
Response of the operating system
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
LED "INTF" remains lit until the error is
eliminated.
Call of OB 80.
If the OB is not loaded: CPU changes
to STOP mode.
Call of OB 81
If the OB is not loaded: The CPU
remains in RUN.
System Manual, 03/2012, A5E00267695-11
Error LED
EXTF
INTF
EXTF
S7-400H