Recursive digital filter circuitry which avoids persistent unstable conditions therein provides a serial clock signal, a synchronization signal, and a serial data input to corresponding inputs of a 3-wire serial interface circuit to produce a serial clock output signal, a synchronization output signal, and a parallel data output signal which are applied to corresponding inputs of a recursive digital filter. The serial clock signal and the synchronization signal are input to an auto-reset circuit which detects a fault associated with the synchronization signal or the serial clock signal and produces a reset signal in response to detection of the fault for resetting the recursive digital filter.