Siemens SIMATIC FM 456-2 Installation, Hardware, And Startup page 59

Table 4-3 FM 456-2 Mode Selector Positions
Mode Selector
Position
STOP
MRES
Activating MRES
To effect a hardware reset via MRES, proceed as follows:
1. Turn the mode selector to the STOP position.
Result:
2. Turn the mode selector to MRES and hold it in this position.
Result:
goes out for 1 second and then lights up steadily.
3. Turn the mode selector back to the STOP position, to the MRES position again
and back to the STOP position within 3 seconds.
Result:
reset being carried out) and then lights up again.
4. If the STOP indicator does not flash or other indicators light or flash, steps 2
and 3 must be repeated.
Note
The resetting of the module by activating MRES is controlled by the system
software. If this has not been started, the FM 456-2 must be reset, if necessary, by
switching the power on and off. If a keyboard is connected to the FM 456-2, it is
possible to initiate a cold start via the hotkeys CTRL+ALT+HOME.
FM 456-2 Application Function Module Installation, Hardware, and Startup
C79000-G7076-C458-01
The user program on the FM 456-2 cannot access the I/O
modules. The user program cannot control the process.
The key can be removed in this position to prevent unauthorized
change of mode.
Spring-return position of the key switch for software-controlled re-
set of the FM 456-2 (hardware reset).
The STOP indicator lights up
The STOP indicator goes out for 1 second, lights up for 1 second,
The STOP indicator flashes for at least 3 seconds at 2 Hz (general
FM 456-2 Functions and Technical Data
Explanation
4-5