Sinumerik Alarm 120201 Communication failure
The operator panel is connected with the NC and PLC via a serial bus. This alarm occurs when the communication to these components is interrupted. In connection with this alarm, all display values connected with the NC/PLC become invalid. Such faults are normal while the controls are ramping up (e.g. after resetting).
– Alarm display.
The alarm disappears automatically as soon as the fault situation has ended. If this alarm is continuously present, a wide variety of faults may be the cause. (e.g. wire breakage, NC/PLC not ramped up, faulty address/data transfer rate configuration of one of the bus nodes, etc.).
- Siemens Diagnostics Guide by Siemens