Commissioning
6-7
AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
6.5 Resetting the CPU with the Mode Selector Switch

How to Carry Out a Memory Reset

When you reset a CPU, you place the memories of the CPU in a defined initial
state. The CPU also initializes its hardware parameters and some of the system
program parameters. If you have inserted a Flash card with a user program in the
CPU, the CPU transfers the user programand the system parameters stored on
the Flash card into the main memory after the memory reset.

When Should a CPU be Reset?

Youmust reset the CPU:
•Before transferring a new,complete user program to the CPU.
•When the CPU requests a reset. Yourrecognize this request by slow flashing of
the STOP LED at 0.5 Hz.

How to Perform a Memory Reset

There are two ways of resetting the CPU:
•Reset with the mode selector switch
•Reset from the programming device (see STEP 7)
Resetting the CPU with the mode selector is described in the following section.