1. A method for decoding digitally encoded transmission signals where transitions within the transmission signal represent a combination of transmitted clock and data signals, the frequency of the transmitted clock signal is known, successive transitions over a period of time equal to one transmitted clock or bit cycle represent one transmitted clock cycle and a transmitted data signal of one polarity, and successive transitions over one bit cycle with an additional transition occurring mid-way through the bit cycle represent a transmitted clock cycle and a transmitted data signal of the opposite polarity, comprising the steps of: sampling the transmission signal at a rate equal to some multiple of the transmitted clock frequency; detecting whether or not a transition of the transmission signal occurred within said sample; timing the difference between successive transitions; decoding each transition as the most probable of either the start of a new bit cycle or a mid-bit transition according to the known length of a bit cycle wherein a transition occurring before a 3/4 bit time interval after the start of a new bit cycle is decoded as a mid-bit transition while a transition occurring after the 3/4 bit time interval is decoded as the start of a new bit cycle; and deferring the decoding decision for a first transition which occurs within a sample time containing the 3/4 bit time interval after the start of a new bit cycle until a second transition occurs, at which time the first transition is decoded as a mid-bit transition if the second transition occurs before a specified time interval after the first transition and decoded as the start of a new bit cycle otherwise.