Siemens S5-155U System Manual page 197

CPU 922
Status indicators
5 - 48
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
flashing reset has been requested. This request can be
initiated by the CPU itself or by operator
action.
System Manual
C79000-B8576-C199-03