Siemens Automation System S7-400 - Manual (Page 137)

Commissioning
6-9
Automation System S7-400 Hardware and Installation
A5E00850741-01
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.