Responding To Fatal Errors - Siemens SIMATIC S7-200 System Manual

Basic Concepts for Programming an S7-200 CPU

Responding to Fatal Errors

Fatal errors cause the CPU to stop the execution of your program. Depending
upon the severity of the fatal error, it can render the CPU incapable of performing
any or all functions. The objective for handling fatal errors is to bring the CPU to a
safe state from which the CPU can respond to interrogations about the existing
error conditions. When a fatal error is detected by the CPU, the CPU changes to
the STOP mode, turns on the System Fault LED and the STOP LED, and turns off
the outputs. The CPU remains in this condition until the fatal error condition is
corrected.
Once you have made the changes to correct the fatal error condition, you must
restart the CPU. You can restart the CPU by using one of these methods:
Turning the power off and then on
Changing the mode switch from RUN or TERM to STOP
Use STEP 7-Micro/WIN to restart the CPU. STEP 7-Micro/WIN 32 implements
the PLC > Power-Up Reset from the main menu bar. This forces the PLC to
restart and clear any fatal errors.
Restarting the CPU clears the fatal error condition and performs power-up
diagnostic testing to verify that the fatal error has been corrected. If another fatal
error condition is found, the CPU again sets the fault LED indicating that an error
still exists. Otherwise, the CPU begins normal operation.
There are several possible error conditions that can render the CPU incapable of
communication. In these cases, you cannot view the error code from the CPU.
These types of errors indicate hardware failures that require the CPU to be
repaired; they cannot be fixed by changes to the program or clearing the CPU
memory.
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S7-200 Programmable Controller System Manual
A5E00066097-02