Siemens S5-135U/155U System Manual page 162

CPUs, Memory Cards, Memory Submodules, Interface Submodules
Status Indicators
Given in the following overview are the functions of the RUN, STOP and
SYS FAULT status LEDs.
The STOP LED indicates a soft stop; the SYS FAULT LED indicates a hard
STOP.
The CPU 948 can process a user program (OB 39) cyclically at the soft
STOP, but the digital outputs remain inhibited. At the hard STOP, no program
can run and the CPU has "stopped." This state can only be exited by
switching the system voltage off and on again.
RUN
LED
5-22
STOP SYS Status
LED FAULT
LED
on off off The CPU is in the RUN state (cyclic
operation).
on on on Appears briefly after power-up of the unit.
off off off CPU is in the initial start or program check
state.
off on off CPU is in the soft STOP state.
off rapid off CPU is in the soft STOP state.
flashing Overall reset has been requested by switch or
from the operating system.
off slow off CPU is in the soft STOP state. An error has
flashing occurred; see the CPU 948 Programming
Guide for possible causes.
off off on CPU is in the hard STOP state. No program
processing is taking place. You can only exit
from this state by switching the system
voltage off and on again.
System Manual
C79000-G8576-C199-06