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

Installation of a CPU 41x-H
4-6
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07
4.2 Monitoring Functions of the CPU
Monitoring and Error Messages
The CPU hardware and the operating system have monitoring functions that
ensure that the system functions correctly and that there is a defined response to
an error. A number of errors will also produce a response from the user program.
The following table gives you an overview of possible errors, their causes and the
responses of the CPU.
There are also test and information functions available in each CPU that you can
call up with STEP 7.
Type of
Fault/Error
Cause of Error Response of the Operating
System
Error LED
Clock pulse
failure
Monitoring of the failure of the processor
clock pulse
System standstill
Disabling of the digital outputs by
issuing the “OD” (Output Disable)
signal
–
Access error Module failure (SM, FM, CP) “EXTF” LED lights up until the fault is
acknowledged.
In SMs:
• OB 122 call
• Entry in the diagnostics buffer
• In the case of input modules:
Entry of null for the date in the
accumulator or the
process image
In the case of other modules:
• OB 122 call
EXTF
Timing error • The runtime of the user program (OB1
and all the interrupts and error OBs)
exceeds the specified maximum cycle
time.
• OB request error
• Overrun of the start information buffer
• Time error interrupt
“INTF” LED lights up until the fault is
acknowledged.
OB 80 call
If the OB is not loaded: The CPU
goes into STOP mode.
INTF
Power supply
module error
(not power
failure)
In the central or distributed I/O rack:
• At least one backup battery in the
power supply module is empty.
• The backup voltage is missing.
• The 24 V supply to the power supply
module has failed.
OB 81 call
If the OB is not loaded: The CPU
continues to run.
EXTF
Diagnostics
Interrupt
An I/O module with interrupt capability
reports a diagnostics interrupt.
OB 82 call
If the OB is not loaded: The CPU
goes into STOP mode.
EXTF
Remove/insert
interrupt
Removal or insertion of an SM and
insertion of an incorrect module type. If the
only inserted SM is removed during STOP
mode of the CPU with default parameter
assignment, the EXTF LED will not light up.
If the SM is inserted again, the LED lights
up briefly.
OB 83 call
If the OB is not loaded: The CPU
goes into STOP mode.
EXTF