Siemens CPU 313C Hardware And Installation Manual page 161

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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 the following CPUs are used, we recommend that you use the more user-friendly
SFB 54 RALRM (called in diagnostic OB82) to evaluate the diagnostics from
centralized or distributed modules or DP slaves:
• CPU 31xC, FW Version V 2.0.0 and higher
• CPU 312, FW Version V 2.0.0 and higher
• CPU 314, FW Version V 2.0.0 and higher
• CPU 315-2 DP, FW Version V 2.0.0 and higher
• CPU 317-2 DP, FW Version V 2.1.0 and higher
Further options for diagnostics with system functions are listed below:
• 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 SFC 13
"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.
• Reading a data record with SFC 59 "RD_REC"
You can use SFC 59 "RD_REC" (read record) to read a specific data record
from the addressed module. Data records 0 and 1 are especially suitable for
reading diagnostic information from a diagnosable module.
Data record 0 contains 4 bytes of diagnostic data describing the current state of
a signal module. Data record 1 contains the 4 bytes of diagnostic data also
stored in data record 0, plus module-specific diagnostic data.
• Reading out the start information of the current OB, using SFC 6 "RD_SINFO"
Error information is also found in the start information of the relevant error OB.
You can use SFC 6 "RD_SINFO" (read start information) to read the start
information of the OB that was last called and not yet processed completely,
and of the start-up OB that was last called.
S7-300 Automation System, Hardware and Installation: CPU 31xC and CPU 31x
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