Siemens Simatic S7-400 - Manual (Page 438)

CPUs for M7-400
11-10
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Table 11-5 Positions of the Mode Selector Switch
Position of
the Mode
Selector
Switch
Explanations
STOP I/O access is disabled for the user program of the CPU. The user
program cannot control the process.
The key can be removed in this position to prevent any unauthorized
persons from changing the operating mode.
MRES Position of the keyswitch for software-controlled resetting of the CPU
(hardware reset).
Activating MRES
To generate a hardware reset via MRES, follow the steps outlined below:
1. Turn the mode selector switch to the STOP position.
Result: The STOP LED lights up.
2. Turn the mode selector switch to the MRES position and hold it there.
Result: The STOP LED goes dark for a second, lights up for a second, goes
dark again, and then remains lit.
3. Turn the switch back to the STOP position and then, in the next 3 seconds, to
the MRES position again and back to STOP.
Result: The STOP LED flashes for approximately 3 seconds at 2 Hz (a memory
reset is being carried out) and then remains lit.
4. If the STOP LED does not flash or other LEDs light up or flash, you must repeat
steps 2 and 3.
Note
Resetting by activating MRES is controlled by the system software. If this has not
been started, the CPU must be reset by switching the power supply off and on. If a
keyboard is connected to the CPU, it is also possible to initiate a complete restart
via hot keys (see Table 11-7 on page 11-19).