Commissioning
8.4 Commissioning the Modules
S7-300, CPU 31xC and CPU 31x: Installation
Operating Instructions, Edition 08/2004, A5E00105492-05
8-9
8.4.2 Initial power on
Requirements
• You must have installed and wired up the S7-300.
• The MMC is inserted in the CPU.
• Your CPU's mode selector switch must be set to STOP.
Initial power on of a CPU with Micro Memory Card (MMC)
Switch on the PS 307 power supply module.
Result:
• The 24 VDC LED on the power supply module is lit.
• The 5 VDC LED on the CPU
– is lit.
– The STOP LED flashes at 2 Hz when the CPU executes an automatic memory reset.
– The STOP LED is lit after memory reset.
8.4.3 CPU memory reset by means of mode selector switch
When to reset CPU memory
You reset CPU memory
• before you download a (completely) new user program to the CPU
• when the CPU requests a memory reset with its STOP LED flashing at 0.5 Hz intervals
Possible reasons for this request are listed in the table below.
Table 8-3 Possible reasons of a CPU request to reset memory
Causes of a CPU request to reset memory Special features
The MMC has been replaced –
RAM error in CPU –
Main memory is too small, that is, all blocks
of the user program on an MMC cannot be
loaded.
Attempts to load faulty blocks; if a wrong
instruction was programmed, for example.
CPU with MMC: Recursive request of a CPU memory
reset.
For further information on the behavior of the MMC
during CPU memory reset, refer to the CPU 31xC and
CPU 31x Manual, Technical Data, under
Memory Reset
and Restart
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