Cause : PU communication comes when communication errors detected between the drive control unit and the power unit.

The fault code 5681 in your ABB ACS560 drive indicates a communication error between the drive control unit and the power unit. This means the essential communication link between the "brains" (control unit) and the "muscle" (power unit) of the drive is disrupted. Consequently, the drive cannot function properly.

1. Check the connection between the drive control unit and the power unit.
2. Check the value of parameter 95.04 Control board supply.