Siemens S7-400 Installation Manual page 158

Starting Up
Resetting the CPU with the Mode Selector Switch
The mode selector switch is designed as a keyswitch. The following figure shows
the possible positions of the mode selector switch.
Proceed as follows to reset the CPU using the mode switch:
Case A: You want to transfer a new, complete user program to the CPU.
1. Turn the switch to the STOP setting.
Result: The STOP LED lights up.
2. Turn the switch to the MRES setting and keep it at this setting.
Result: The STOP LED is dark for one second, bright for one second, dark for
one second and then remains lit.
3. Turn the switch back to the STOP setting, then to the MRES setting again within
the next 3 seconds and back to STOP.
Result:The STOP LED flashes for at least 3 seconds at 2 Hz (reset is being
executed) and then remains lit.
Case B: The CPU requests a reset by slow flashing of the STOP LED at 0.5 Hz
(system reset request, for example, when a memory card has been removed or
inserted).
Turn the switch to the MRES setting and back to the STOP setting.
Result:The STOP LED flashes for at least 3 seconds at 2 Hz (reset is being
executed) and then remains lit.
6-8
RUN-P
RUN
STOP
MRES
S7-400 and M7-400 Programmable Controllers Hardware and Installation
A5E00069481-04