Abstract: An optical isolator for use in an electrically powered vehicle for interfacing between a signal processing system having a first ground and a power conversion system, which is operated responsive to control signals from the signal processing system, having a second ground that varies in potential from the first ground. A bi-directional digital communications network is provided having a first node coupled to the signal processing system for generating and receiving digital messages with respect to the first ground, and having a second node coupled to the power conversion system for receiving and generating digital messages with respect to the second ground. The bi-directional digital communications network has a unique start signal and a dominant hierarchy that allows bit-wise contention among messages for assuring communication of high priority messages between the first and second nodes within a predetermined minimum time period.