Phase encoding

In telecommunication and data storage, Manchester coding (also known as phase encoding, or PE) is a line code in which the encoding of each data bit is either low then high, or high then low, of equal time. It therefore has no DC bias, and is self-clocking, which means that it may be inductively or capacitively coupled, and that a clock signal can be recovered from the encoded data. As a result, electrical connections using a Manchester code are easily galvanically isolated using a network isolator—a simple one-to-one isolation transformer.

The name comes from its development at the University of Manchester, where the coding was used to store data on the magnetic drum of the Manchester Mark 1 computer.

Phase encoding (PE) was widely used for magnetic recording on 1600 bpi computer tapes before the introduction of 6250 bpi tapes which used the more efficient group-coded recording.

Manchester coding is widely used (e.g., in 10BASE-T Ethernet (IEEE 802.3); consumer IR protocols; see also RFID or near field communication). There are more complex codes, such as 8B/10B encoding, that use less bandwidth to achieve the same data rate but may be less tolerant of frequency errors and jitter in the transmitter and receiver reference clocks.

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