A128 Fieldbus communication loss alarm in ABB DCS800 drive indicates a loss of communication with a fieldbus network. This can disrupt the drive's control and monitoring capabilities, leading to operational issues.

F528 FieldBusCom is only activated after the first data set from the overriding control is received by the drive. Before the first data set is received only A128 FieldBusCom is active. The reason is to suppress unnecessary faults (the start up of the overriding control is usually slower than the one of the drive).

1. Check parameter settings of group 51 (fieldbus).
2. Check fieldbus cable.
3. Check fieldbus termination.
4. Check fieldbus adapter.