Siemens S5-155U System Manual page 196

Mode switch
RUN
STOP
Momentary-contact mode
switch
OVERALL RESET
RESET
Restart
System Manual
C79000-B8576-C199-03
The mode switch has two settings:
In the RUN setting, the CPU 922 processes the user program when the
green RUN LED is lit.
The CPU 922 goes to the stop state when you switch from RUN to
STOP. The red STOP LED then lights up.
You can initiate the Overall Reset, Reset and Restart functions with
the momentary-contact mode switch:
Momentary-contact switch down
With an overall reset, all RAM areas are erased and initialized (both
on the CPU and on a RAM submodule).
Momentary-contact switch up
During a reset, all flags, timers, counters and the process image will be
erased. OB 20 will be invoked. Processing of the user program will
start from the beginning again.
Momentary-contact switch at midpoint
With a restart, processing of the user program will continue from the
point of interruption. The statuses of flags, timers, counters and the
process image are retained during stoppage of the CPU.
CPU 922
5
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