Digital phase decoder with collision detection

A data communication system includes a communicating medium and a plurality of transceivers connected to the medium, each including a transmitter for transmitting phase-encoded data onto the medium and a receiver for receiving phase-encoded data communicated on the medium by another transceiver. A digital phase decoder is coupled to the receiver of each transceiver for decoding the data received and applying at its output a decode signal representative of the character of the received data. The received data comprises a plurality of bitcells each of a predetermined time period with a predetermined number of bitcells representing a data packet. The decoder includes a combination signal generating means and counter means to ascertain, relative to each bitcell in a packet, where any transitional change has occurred in relation to each packet bitcell, the point of occurrence being representative of one of several possible conditions relative to the decoded signal, those conditions being indicative of either a data transition from a low state to a high state or a data transition from a high state to a low state or an illegal transition treated as a data collision.