Siemens S5-135U/155U - Manual (Page 176)

5-36
System Manual
C79000-G8576-C199-06
The mode switch has two settings:
In the RUN setting, the CPU 928B processes the user program when the
green RUN LED is lit.
The CPU 928B 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.
Mode Switch
RUN
STOP
Momentary-
Contact Mode
Switch
OVERALL RESET
Reset
Restart
CPUs, Memory Cards, Memory Submodules, Interface Submodules