6681 fault in ABB DCS880 drive indicates EFB communication issue. This means cyclical communication to the embedded fieldbus (EFB) is lost.

6681 EFB communication 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 A7CE EFB communication is active. The reason is to suppress unnecessary faults (the
startup of the overriding control is usually slower than the one of the drive).

1. Check the status of the fieldbus master (online, offline, error etc.).
2. Check the settings of group 58 FBA Embedded fieldbus.
3. Check the cable connections to connector XD2D on the control board.
4. Check the fieldbus termination.