Line code

A line code maps data to a sequence of physical signal levels or transitions for transmission. Timing, polarity and the length of runs of equal levels affect the choice.

A block code for line coding maps fixed-size groups of data bits to fixed-size transmitted codewords, chosen to meet signal constraints as well as to distinguish inputs. Constraints on long runs must also be checked across word boundaries.

Differential Manchester encoding has a transition at every bit midpoint and encodes the data by the presence or absence of a boundary transition. A consistent signal polarity reversal preserves those transition decisions.

Manchester encoding represents each data bit by two opposite half-bit levels. The compulsory midpoint transition supports clock recovery.

Clock recovery extracts a timing reference from a received signal so that a receiver can locate symbol boundaries.