Siemens S5-135U/155U System Manual page 207

Status Indicators
System Manual
C79000-G8576-C199-06
CPUs, Memory Cards, Memory Submodules, Interface Submodules
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.
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