Siemens S5-135U/155U System Manual page 178

CPUs, Memory Cards, Memory Submodules, Interface Submodules
ADF LED
ZYK LED
BASP LED
A detailed description of interrupt and error handling can be found in the
CPU 928B -3UB21 Programming Guide.
LED SI1
5-38
on The user program has referenced an I/O address in the
process image under which no module is inserted.
on The maximum cycle monitoring time has been exceeded.
on Command output is inhibited and the digital outputs will be
directly switched to the safe state.
LED SI2 Cause
on on No communication possible at both interfaces.
Internal error.
on off SI1:
No communication possible.
Internal error.
SI2:
If used, interface is initialized and ready.
off on SI1:
Interface is initialized and ready.
SI2:
No communication possible.
Wrong interface submodule inserted or wrong
parameters for interface or internal error.
off off First interface and, if used, second interface are
initialized and ready.
System Manual
C79000-G8576-C199-06