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 zero, and does not have a transition if the bit being transmitted is a logical one.

This is the code used on compact discs, USB, and on 100BASE-FX fiber Fast Ethernet.

For example, imagine a data stream is containing the bit sequence "01001101", and assume the initial state to be '1'. That bit stream will be transmitted with NRZI as "LLHLLLHH", with "L" corresponding to a low signal level and "H" corresponding to a high signal level. Similarly if the initial state were '0', then that bit stream will be transmitted as "HHLHHHLL".

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.

Line codes

NRZI | Codage NRZI | NRZI