Commissioning
S7-300 Programmable Controller Hardware and Installation
A5E00105492-01
8-15
CPU memory reset with the mode selector switch
The table below shows the steps required for resetting CPU memory.
Table 8-4 Procedure for CPU memory reset
Step Resetting CPU memory
1. Turn the key to STOP position
2. Turn the key to the MRES position and push it in 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.
3. You must turn the switch back to the MRES position and push it in within three
seconds. Keep it in this position 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.
The procedure described in the table above are only required if the user want to
reset CPU memory, without being requested by the CPU to reset memory (slow
flashing of the STOP LED). Memory reset requested by the CPU itself is started by
briefly turning the mode selector switch to MRES position.
The figure below shows the sequence of operation.
t
On
Of
3s
max. 3 s
min. 3 s
STOP-
LED
1
2
3
CPU 31x
CPU 31xC
Figure 8-8 Sequence of operation for resetting CPU memory with the mode selector switch
In specific cases you might have to format the MMC if the CPU requests memory
reset again after a successful reset. Refer to the CPU Data Manual, Chapter
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