Siemens S5-155U System Manual page 164

CPU 948
Fault LEDs SI1 and SI2
5 - 14
LEDs SI1 and SI2 indicate faults in communication via interfaces SI1
and SI2:
LED SI1 LED SI2 Cause
on on Communication is not possible at both
interfaces. Internal fault.
on off SI1:
No communication possible.
Internal fault.
SI2:
Interface is initialized and ready.
LED SI2 is always off if no interface module is
inserted.
off on SI1:
Interface is initialized and ready.
SI2:
No communication possible.
Wrong module inserted or internal fault.
off off Both interfaces are initialized and ready.
LED SI2 is always off if no interface module is
inserted.
System Manual
C79000-B8576-C199-03