Manchester encoding
Manchester encoding
(communications, protocol)A simple way of signalling bits might be to transmit a highvoltage for some period for a 1-bit and a low voltage for a 0bit:
Bits Sent: 1 1 0 0
Signal: High ___________Low |___________
Time: -> . . . . .
However, when several identical bits are sent in succession,this provides no information to the receiver about when eachbit starts and stops.
Manchester encoding splits each bit period into two, andensures that there is always a transition between the signallevels in the middle of each bit. This allows the receiver tosynchronise with the sender.
In normal Manchester encoding, a 1-bit is transmitted with ahigh voltage in the first period, and a low voltage in thesecond, and vice verse for the 0 bit:
Bits Sent: 1 1 0 0
Signal: High __ __ __ __Low |__| |_____| |__|
Time: -> . ' . ' . ' . ' .
In Differential Manchester encoding, a 1-bit is indicated bymaking the first half of the signal equal to the last half ofthe previous bit's signal and a 0-bit is indicated by makingthe first half of the signal opposite to the last half of theprevious bit's signal. That is, a zero bit is indicated by atransition at the beginning of the bit.
Like normal Manchester encoding, there is always a transitionin the middle of the transmission of the bit.
Differential Manchester Encoding
Bits Sent: 1 1 0 0
Signal: High ____ __ __ __Low |_____| |__| |__|
Time: -> . ' . ' . ' . ' .
With each bit period half as long, twice as much bandwidthis required when using either of the Manchester encodingschemes.