Siemens S7-300 Installation Manual page 164

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• Reading a data record with SFC59 "RD_REC"
You can use SFC59 "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 SFC6 "RD_SINFO"
Error information is also found in the start information of the relevant error OB.
You can use SFC6 "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.
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Locate the cause of a module error by viewing the online information on the
module. You can locate the cause of an error in the user program cycle with the
help of the diagnostic buffer and of the stack content. You can also check whether
a user program will run on a specific CPU.
Hardware diagnostics give you an overview of the PLC status. In an overview
symbols can display the error status of every module. A double-click on the faulty
module opens detailed error information. The scope of this information depends on
the specific module. You can view the following information:
• Display of general information on the module (e.g. order No., version,
designation) and module status (e.g. error).
• Display of module errors (e.g. channel error) in the central I/O and DP slave.
• Display of messages from the diagnostic buffer.
For CPUs you can also view the following module status information:
• Cause of an error in the user program cycle.
• Display of the cycle time (longest, shortest and last cycle).
• Options and utilization of MPI communication.
• Display of performance data (number of possible /IOs, memory bits, counters,
timers and blocks).
Details on diagnostic options in STEP 7 and procedures are found in the
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11-6
S7-300 Automation System, Hardware and Installation: CPU 312IFM - 318-2 DP
A5E00203919-01