NRZ Encoding Non-return to zero encoding is used in slow speed synchronous and asynchronous transmission interfaces. With NRZ, a logic 1 bit is sent as a high value and a logic 0 bit is sent as a low value [really no encoding at all]. The receiver may lose synchronization when using NRZ to encode a synchronous link which may have long runs of consecutive bits with the same value [no changes in voltage].
Other problems with NRZ include; Data sequences containing the same number of 1's and 0's will produce a DC level, and NRZ requires a large bandwidth, from 0Hz [for a sequence containing only 1's or only 0's] to half of the data rate [for a sequence of 10101010].
"A type of 'null' encoding, where a logical 'zero' is represented by a particular line state, and a logical 'one' by another. In other words, there is no encoding, as distinct from RZ encoding." NRZ is used with RS-232 and CANbus.
NRZ Encoding
There are other variations of NRZ encoding; which include:
NRZ-L: [Non-Return-to-Zero-Level]: In NRZ-L encoding, the polarity of the signal changes only when the incoming signal changes from a one to a zero or from a zero to a one. NRZ-L method looks just like the NRZ method, except for the first input one data bit. This is because NRZ does not consider the first data bit to be a polarity change, where NRZ-L does.
NRZ-M [Non-Return-to-Zero-Mark (NRZ-M) Encoding]: The polarity of the signal changes when the incoming signal is a one. An incoming zero would not change the polarity of the signal.
NRZ-S [Non-Return-to-Zero-Space (NRZ-S) Encoding]: Works just like NRZ-M, except the signal changes when the incoming data signal is a zero, not when the signal is a one.
NRZ-C [Non-Return-to-Zero-Change Encoding]: Same as NRZ-L.
NRZI [Non-Return-to-Zero-Inverted Encoding]: A '0' is encoded as no change in the level. However a '1' is encoded depending on the current state of the line. If the current state is '0' [low] the '1' will be encoded as a high, if the current state is '1' [high] the '1' will be encoded as a low. Used with FDDI and USB for example.
NRZI Encoding
