Manchester encoding
<communications, protocol> A method of transmitting bits which enables
the receiver to easily synchronise with the sender.
A simple way of signalling bits might be to transmit a high voltage for some
period for a 1-bit and a low voltage for a 0 bit:
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 each bit
starts and stops.
Manchester encoding splits each bit period into two, and ensures that there is
always a transition between the signal levels in the middle of each bit. This
allows the receiver to synchronise with the sender.
In normal Manchester encoding, a 1-bit is transmitted with a high voltage in the
first period, and a low voltage in the second, 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 by making the
first half of the signal equal to the last half of
the previous bit's signal and a 0-bit is indicated
by making the first half of the signal opposite to
the last half of the previous bit's signal. That is,
a zero bit is indicated by a transition at the
beginning of the bit.
Like normal Manchester encoding, there is always a transition in 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 bandwidth is required
when using either of the Manchester encoding
schemes.
(1995-11-23)
Nearby terms:
Management Information System « Manager of Business
Applications « Manchester Autocode « Manchester
encoding
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