Siemens SIMATIC S7 Manual page 28

Missing or Wrong
Licensing
!
OPEN MODBUS / TCP communication via CP343-1 and 443-1
2XV9450-1MB00; Manual edition 4.3
When the registration key is missing or a wrong one is detected, the SF LED
(S7-300) or the INTF LED (S7-400) of the CPU is flashing. A cyclic error
message regarding the missing license is displayed in the diagnostic buffer
too. The error number of the missing license is W#16#A090.
_____________________________________________________________
Warning
The CPU will turn to STOP mode, if the OB121 is not available.
_____________________________________________________________
Modbus communication is carried out even with a missing or wrong
registration key, but the output STATUS is set to W#16#A090 "no valid
license".
Licensing
4-4