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differential manchester encoding (DME)

Differential Manchester Encoding (DME) or Conditioonal Diphase (CDP) is used in token ring networks and 10 Gigabit Ethernet (10GbE) and is specified in IEEE 802.5.

In differential Manchester coding, the state changes in the middle of each bit. The transition direction always changes at a logical "1", namely from Hi to Low. With a logical "0", the level change corresponds to that of the clock signal. Differential Manchester coding results from an XOR operation of the clock signal and an NRZ-I coded signal, Non Return to Zero Inverted (NRZ-I).

Differential Manchester Coding

Differential Manchester Coding

In 10GbE, DME coding operates at 312.5 MBaud, or a cycle time of 6.4 ns, during autonegotiation. The encoding state changes from a bitcell to a 1-state in the middle of each cycle. If the bit cell corresponds to a "0", then there is no level change in the differential Manchester encoding used in 10-gigabit Ethernet; the "0" is represented by a logical Hi level. DME-coded signals have a balanced DC level.

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Englisch: differential manchester encoding - DME
Updated at: 10.02.2014
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