Danfoss · VLT Micro Drive FC 51
This fault indicates that the drive has not received a valid control word via serial communication (e.g., Modbus RTU) within the configured timeout period. This typically means a break in communication, preventing the drive from receiving commands and potentially stopping the motor.
Click steps to track your progress.
Visually inspect the RS-485 communication cable (e.g., twisted pair, shielded) for physical damage or loose connections at terminals (e.g., DA+, DB-).
Verify the Modbus communication settings (P5-00 to P5-05) on the drive match those configured in the Modbus master device (e.g., PLC program).
Monitor the communication line using a Modbus sniffer tool or oscilloscope to observe data packets and ensure control words are being sent.
Check for correct termination resistors (e.g., 120 Ohm) on the RS-485 bus, especially at the ends of the segment.
Temporarily connect a known good Modbus master (e.g., PC with Modbus poll software) to the drive to isolate the fault source.