Fatal Errors - Siemens SIMATIC S7-200 System Manual

The module status information is stored in special memory (SM) bits. Your program can monitor
and evaluate these bits. Refer to Appendix D for more information about the SM bits used for
reporting I/O errors. SM5.0 is the global I/O error bit and remains set while an error condition
exists on an expansion module.
Program execution errors
Your program can create error conditions while being executed. These errors can result from
improper use of an instruction or from the processing of invalid data by an instruction. For
example, an indirect-address pointer that was valid when the program compiled could be modified
during the execution of the program to point to an out-of-range address. This is an example of a
run-time programming problem. SM4.3 is set upon the occurrence of a run-time programming
problem and remains set while the S7-200 is in RUN mode. (Refer to Appendix C for the list of
run-time programming problems). Program execution error information is stored in special memory
(SM) bits. Your program can monitor and evaluate these bits. Refer to Appendix D for more
information about the SM bits used for reporting program execution errors.
The S7-200 does not change to STOP mode when it detects a non-fatal error. It only logs the
event in SM memory and continues with the execution of your program. However, you can design
your program to force the S7-200 to STOP mode when a non-fatal error is detected. The following
sample program shows a network of a program that is monitoring two of the global non-fatal error
bits and changes the S7-200 to STOP whenever either of these bits turns on.
Sample Program: Logic for Detecting a Non-Fatal Error Condition

Fatal Errors

Fatal errors cause the S7-200 to stop the execution of your program. Depending upon the severity
of the fatal error, it can render the S7-200 incapable of performing any or all functions. The
objective for handling fatal errors is to bring the S7-200 to a safe state from which the S7-200 can
respond to interrogations about the existing error conditions. When a fatal error is detected, the
S7-200 changes to STOP mode, turns on the SF/DIAG (Red) and the STOP LED, overrides the
output table, and turns off the outputs. The S7-200 remains in this condition until the fatal error
condition is corrected.
Once you have made the changes to correct the fatal error condition, use one of the following
methods to restart the S7-200:
Turn the power off and then on.
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Change the mode switch from RUN or TERM to STOP.
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Select the PLC > Power-Up Reset menu command from STEP 7--Micro/WIN to restart the
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S7-200. This forces the S7-200 to restart and clear any fatal errors.
Restarting the S7-200 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 S7-200
again sets the fault LED, indicating that an error still exists. Otherwise, the S7-200 begins normal
operation.
Some error conditions can render the S7-200 incapable of communication. In these cases, you
cannot view the error code from the S7-200. These types of errors indicate hardware failures that
require the S7-200 to be repaired; they cannot be fixed by changes to the program or clearing the
memory of the S7-200.
Programming Concepts, Conventions, and Features
Network 1 //When an I/O error or a run-time error occurs,
//go to STOP mode
LD SM5.0
O SM4.3
STOP
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