coded mark inversion (CMI)
Coded Mark Inversion (CMI) is a method for coding binary signals. This code is based on a change of the coded state during the clock time of the binary signal.
In the CMI code, a digital "0" is represented with the negative amplitude in the first half of the clock time, and in the second half of the clock time, the "0" is represented with the positive amplitude. The digital "1", on the other hand, is represented either with the positive value or with the negative amplitude value during the entire clock time; however, alternating. In this way, the coding achieves freedom from direct current in the transmission.
CMI coding is used, for example, in the E transmission interfaces for E-4.