Commissioning
8.4 Commissioning the Modules
S7-300, CPU 31xC and CPU 31x: Installation
8-10
Operating Instructions, Edition 08/2004, A5E00105492-05
How to reset memory
There are two ways to reset CPU memory:
CPU memory reset using the mode selector
switch
CPU memory reset using the PG
... is described in this chapter.
... is only possible when the CPU is in STOP
(see
STEP 7 Online Help
).
Resetting CPU memory with mode selector switch
The table below shows the steps in resetting CPU memory.
Table 8-4
Procedure for CPU memory reset
Step
Reset CPU memory
1.
Turn the key to STOP position
2.
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). Now release the key.
3.
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.
The procedure described in the table above is only required if the user wishes to reset the
CPU memory without being requested by the CPU to reset the memory (STOP LED flashing
slowly). If the CPU prompts you for a memory reset, you only have to turn the mode selector
briefly to MRES position to initiate the memory reset operation.
The figure below shows how to use the mode selector switch to reset CPU memory:
t
on
off
3 s
max. 3 s
min. 3 s
STOP-
LED
CPU
1
2
3
If the CPU prompts you for another memory reset following a successful memory reset
operation, the MMC may need to be reformatted in certain cases (
see Formatting a Micro
Memory Card (MMC)).
