Siemens S5-135U/155U System Manual page 198

CPUs, Memory Cards, Memory Submodules, Interface Submodules
Mode Switch
The mode switch has two settings:
RUN
In the RUN setting, the CPU 928-3UA21 processes the user program when
the green RUN LED is lit.
STOP The CPU 928-3UA21 goes to the stop state when you switch from RUN to
STOP. The red STOP LED then lights up.
Momentary- You can initiate the Overall Reset, Reset and Restart functions with the
Contact Mode momentary-contact mode switch:
Switch
OVERALL RESET Momentary-contact switch down
With an overall reset, all RAM areas are erased and initialized.
RESET
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.
Restart
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.
Status Indicators
5-58
RUN STOP Status
LED LED
on off The CPU is in the RUN state.
off on The CPU is in the STOP state. After a stop
request by switch or PG function, the STOP LED
is continuously lit because the transition to the
STOP state was requested by the user or, in
multiprocessor operation, by another CPU, and
was not caused by the CPU itself.
off off The CPU is in the INITIAL START or program
check state.
off slow The CPU is in the STOP state. The CPU has
flashing caused a transition to the STOP state (possibly
also for the other CPUs). If you set the mode
switch to STOP, the flashing LED becomes
continuously lit.
off rapid The CPU is in the STOP state. An overall reset
flashing has been requested. This request can be initiated
by the CPU itself or by operator action.
System Manual
C79000-G8576-C199-06