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Non-return-to-zero
 

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Non-return-to-zero




In Telecommunication , a non-return-to-zero (NRZ) Line Code is a Binary code in which "1s" are represented by one Significant Condition and "0s" are represented by another, with no neutral or rest condition, such as a zero amplitude in Pulse Amplitude Modulation (PAM), zero Phase Shift in Phase-shift Keying (PSK), or mid- Frequency in Frequency-shift Keying (FSK). The pulses have more energy than a RZ code, but it does not have a rest state, which means a synchronization signal must also be sent alongside the code.

NRZ is used in the RS-232 serial protocol. Internal computer signals often use this code. Another useful application of this encoding is for Fiber based Gigabit ethernet(1000Base-X)

For given Data Signaling Rate , ''i.e.,'' Bit Rate , the NRZ code requires only half the Bandwidth required by the Manchester Code .

But the drawback for NRZ are:
1. The transmitter and receiver lack the timing synchronization: No two clocks can be exact even in milliseconds.
2. DC blocking: The components block the direct current(DC) so as to stop heat generation. This results in some loss of data.

''Contrast with:'' Return-to-zero .

Source: from Federal Standard 1037C in support of MIL-STD-188 .