Differential Manchester encoding

The differential Manchester Code, in English as Conditional DEPHASE encoding denotes (CDP) is a line code, which is for the transmission of digital signals used. It represents a further development of the Manchester code, and includes like this in the encoding that is necessary for the receiving means of clock recovery clock signal. In this code, a sequence of bits modulates a binary change of the phase position of a clock signal. The differential Manchester code thus represents a form of differential, digital phase modulation, which is commonly referred to as differential phase shift keying ( DPSK ).

The differential Manchester code is comparable to the biphase mark code, but differs in a different phase of the encoded data stream: There is an additional time shift by half a bit cell time necessary to the biphase mark code in the differential Manchester convert code.

In the differential Manchester code, there are two equivalent definitions, which usually following encoding rule is used, as is also shown in the illustration:

• When transmitting a logic zero, the clock signal for output in relation to the previous phase is not inverted ( rotated by 180 ° in phase )
• When transmitting a logic one, the clock signal for output in relation to the previous phase inverted ( rotated 180 ° )

The second possible definition exchanges the values ​​of logic one and logic zero to one another.

The main advantage of differential Manchester encoding is that the polarity of the encoded signal for the correct reception and the decoding is not important. In a conventional balanced signal transmission line pairs on the exchange of the individual conductors to each other has no effect, which helps to reduce the effects of installation errors in the wiring.

A further property of the differential Manchester code, as well as that of the Manchester code, its DC component free of the resulting signal. This means that the DC component is exactly zero and therefore it is possible to transmit the encoded signal sequence, for example, via pulse transformers for the purpose of galvanic or via fiber optic cable. A disadvantage is that in the data transmission, the bandwidth required is twice as high as for the simple binary code (for example Non Return to Zero, NRZ).

Applies the differential Manchester code in the IEEE 802.5 token-ring networks which describes.

Credentials

• IEEE 802.5 Web Site. Accessed on 24 October 2012.

• Line code