Siemens Simatic S7-400, Installation Manual, Page: 136 / 228

Commissioning
6-8
Automation System S7-400 Hardware and Installation
A5E00850741-01
Resetting the CPU with the Mode Selector Switch
The mode selector switch is designed as a toggle switch. The following figure
shows all positions of the mode selector switch.
RUN
STOP
MRES
Figure 6-2 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. Set the switch to STOP setting.
Result: The STOP LED lights up.
2. Set the switch to MRES and hold it there.
Result: The STOP LED is switched off for one second, on for one second, off
for one second and then remains on.
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).
Set the switch to MRES and then back to STOP.
Result: The STOP LED flashes for at least 3 seconds at 2 Hz (reset is being
executed) and then remains lit.