There are 2 major categories: return–to–zero (RZ)
and nonreturn–to–zero (NRZ). With RZ coding, the
waveform returns to a zero–volt level for a portion (usu-
ally one–half) of the bit interval.
• The waveforms for the line code may be further classified
according to the rule that is used to assign voltage levels
to represent the binary data. Some examples include:
– Unipolar Signalling: In positive–logic unipolar sig-
nalling, the binary 1 is represented by a high level
(+A volts) and a binary 0 by a zero level. This type
of signalling is also called on–off keying (OOK)
February