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Diagnostics
23.8 Flow of Diagnostic Information
Programming with STEP 7
500 Manual, 05/2010, A5E02789666-01
23.8.3 Diagnostic Functions
System diagnostics detect, evaluate, and report errors that occur within a programmable controller.
For this purpose, every CPU and every module with system diagnostics capability (for example,
FM 354) has a diagnostic buffer in which detailed information on all diagnostic events is entered in
the order they occurred.
Diagnostic Events
The following entries are displayed as diagnostic events, for example:
• Internal and external faults on a module
• System errors in the CPU
• Operating mode changes (for example, from RUN to STOP)
• Errors in the user program
• Inserting/removing modules
• User messages entered with the system function SFC52
The content of the diagnostic buffer is retained following a memory reset. Using the diagnostic
buffer, errors in the system can still be analyzed at a later time to find the cause of a STOP or to
trace back and categorize the occurrence of individual diagnostic events
Acquiring Diagnostic Data
You do not need to program the acquisition of diagnostic data by system diagnostics. This is a
standard feature that runs automatically. SIMATIC S7 provides various diagnostic functions. Some
of these functions are integrated on the CPU, others are provided by the modules (SMs, CPs, and
FMs).
Displaying Faults
Internal and external module faults are displayed on the front panels of the module. The LED
displays and their evaluation are described in the S7 hardware manuals. With the S7-300, internal
and external faults are displayed together as a group error.
The CPU recognizes system errors and errors in the user program and enters diagnostic
messages in the system status list and the diagnostic buffer. These diagnostic messages can be
read out on the programming device.
Signal and function modules with diagnostic capability detect internal and external module errors
and generate a diagnostic interrupt to which you can react using an interrupt OB.