Siemens S7-300 Installation Manual page 163

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Notes on diagnostics with LEDs are found in the Chapter below.
Notes on diagnostics of I/O modules capable of diagnostics are found in the
relevant Manual.
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If an error occurs, the CPU writes the cause of error to the diagnostic buffer. In
67(3  you can read the diagnostic buffer with your PG. This location holds error
information in plain text.
Other modules capable of diagnostics can be equipped with their own diagnostic
buffer. In 67(3  (HW Config > Hardware diagnostics) you can read out his buffer
on your PG.
diagnosable modules without diagnostic buffer write their error information to the
CPU's diagnostic buffer.
When an error or an interrupt event occurs, (e.g. time-of-day interrupt), the CPU
switches to STOP mode, or you can react in the user program via error/interrupt
OBs. This would be OB82 in the above example.
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If you are using CPU 318-2 DP with a firmware version >= V 3.0.0, we recommend
the easy-to-use SFB 54 RALRM (call up diagnostic OB82) for diagnostic evaluation
of centralized or distributed modules or DP slaves. In addition, the following system
functions can also be used:
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• Using SFC 51 "RDSYSST" to read an SSL partial list or an extract thereof.
• Reading the diagnostic data (Slave diagnostics) of a DP slave, using SFC13
"DPNRM_DG"
Every DP slave provides slave diagnostic data according to EN 50 170 Volume
2, PROFIBUS. You can use SFC 13 DPNRM_DG" to read these diagnostic
data. Error information is stored in hex code. Refer to the relevant module
manual for information on the meaning of the read code.
For example, the entry of the value 50H (= dual 0101 0000) in byte 7 of the
slave diagnostics for the distributed I/O module ET 200B indicates a faulty fuse
or missing load voltage in channel group 2 and 3.
S7-300 Automation System, Hardware and Installation: CPU 312IFM - 318-2 DP
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