Siemens S7-400 What Happens in the CPU During a Memory Reset, Special Case MPI Parameters

Commissioning

What Happens in the CPU During a Memory Reset

When you carry out a memory reset, the following process occurs in the CPU:

•The CPU deletes the entire user program from the main memory and load memory (integrated RAM and, if applicable, RAM card).

•The CPU clears all counters, bit memory, and timers (except for the time of day).

•The CPU tests its hardware.

•The CPU initializes its hardware and system program parameters, (internal default settings in the CPU). Some programmed default settings will be taken into account.

•If no Flash card is inserted, a reset CPU has a memory utilization level of 0. You can read out the memory utilization level with STEP 7.

•If a Flash card is inserted, the CPU copies the user program and the system parameters stored on the Flash card into the main memory after the reset.

What Remains Following the Memory Reset...

After the CPU has been reset, the following remains:

•The contents of the diagnostic buffer

The contents can be read out with the programming device using STEP 7.

•Parameters of the MPI (MPI address and highest MPI address). Note the special cases in the section below.

•The time of day

•Status and value of the operating hours counter

Special Case MPI Parameters

The MPI parameters are handled in a special mway during a CPU memory reset. If you haev inserted a Memory Card containing the MPI parameters, the system automatically loads these into the CPU and validates the data.

Automation System S7-400	Hardware and Installation	6-9
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