The Non Return to Zero Inverted(NRZ-I) bivalent coding scheme is an inversion of Non Return to Zero (NRZ) and Non Return to Zero Level( NRZ-L).
If the digital signal has a 1, the level of the NRZ-I signal has a low or negative level, if the digital signal represents a 0, the level of the NRZ-I signal is High. There is a logical NOT function between the NRZ-L signal and the NRZ-I signal. If one level is high, the other is low and vice versa.
NRZ-I coding, like NRZ coding, is a simple conversion of the level states with inversion. It has the disadvantage that with long 0 and 1 sequences the synchronization can get out of step.