Non return to zero, inverted (NRZI) is a method of mapping a binary signal to a physical signal for transmission over some transmission media. The two level NRZI signal has a transition at a clock boundary, if the bit being transmitted is a logical one, and does not have a transition if the bit being transmitted is a logical zero.

This is the code used on compact disks.

eg. When the data stream is "01001101", lets assume the initial state to be '1', then transmitted bit stream in NRZI will be "10001001". Similarly if the initial state were '0', then transmitted bit stream will be "01110110".

Return-to-zero, inverted (RZI) is another, and less widely used, method of mapping for transmission. The two-level RZI signal has a pulse (shorter than a clock cycle) if the binary signal is 0, and no pulse if the binary signal is 1.