In This Chapter - Siemens CPU 313C Hardware And Installation Manual

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You must reset CPU memory,
• Before you download a (completely) new user program to the CPU
• If the CPU requests memory reset with its STOP LED flashing at 0.5 Hz
intervals Possible reasons for this request are listed in the table below .
Table 9-3
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The MMC has been replaced
RAM error in CPU
The main memory is too small, that is,
all blocks of the user program on an
MMC cannot be loaded.
Attempts to load faulty blocks; e.g. if
the wrong instruction was
programmed.
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There are two ways to reset CPU memory:
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... is described in this Chapter.
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The table below shows the steps required for resetting CPU memory.
Table 9-4
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1.
2.
3.
S7-300 Automation System, Hardware and Installation: CPU 31xC and CPU 31x
A5E00105492-03
Possible causes for the CPU memory reset request
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Procedure for resetting the CPU memory
Turn the key to STOP position
Turn the key to MRES position. Hold the key in this position until the STOP LED
lights up for the second time and remains on (this takes 3 seconds). Then
release the key.
You must turn the key to MRES position again within 3 seconds and hold it
there until the STOP LED flashes (at 2 Hz). You can now release the switch.
When the CPU has completed memory reset, the STOP LED stops flashing and
remains lit.
The CPU has reset the memory.
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-
CPU with MMC inserted: A further memory reset
is requested.
Additional information on MMC behavior after a
memory reset can be found in the &38 'DWD
Reference Manual, 0HPRU\ FRQFHSW chapter.
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... only possible if the CPU is in STOP mode
(see 67(3  2QOLQH +HOS).
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9-13