non return to zero space (NRZ-S)
The bivalent encoding method Non Return to Zero Space( NRZ-S), in contrast to Non Return to Zero Mark( NRZ-M), works with the space when the digital signal is 0.
While NRZ-M changes the level of the NRZ-M signal on a digital 1, NRZ-S uses the 0 signal to change the level state. At each 0, the NRZ-S signal switches from one level to the other. If the level is previously High, it switches to Low on a digital 0 and vice versa. With a digital 1, the state remains unchanged. With NRZ-S coding, additional level changes are generated for synchronization with long 0 sequences.