Manchester code

In telecommunication, a Manchester code is a code in which (a) data and clock signals are combined to form a single self-synchronizing data stream, (b) each encoded bit contains a transition at the midpoint of a bit period, (c) the direction of transition determines whether the bit is a "0" or a "1," and (d) the first half is the true bit value and the second half is the complement of the true bit value. Contrast with non-return-to-zero.

Source: from Federal Standard 1037C and from MIL-STD-188