Siemens S5-155U System Manual page 162

CPU 948
Status indicators
5 - 12
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 STOP SYS
LED LED FAULT
LED
on off off
on on on
off off off
off on off
off rapid off
flashing
off slow off
flashing
off off on
Status
The CPU is in the RUN state (cyclic
operation).
Appears briefly after power-up of the
unit.
CPU is in the initial start or program
check state.
CPU is in the soft STOP state.
CPU is in the soft STOP state.
Overall reset has been requested by
switch or from the operating system.
CPU is in the soft STOP state.
An error has occurred; see the CPU 948
Programming Guide for possible causes.
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-B8576-C199-03