---
title: "Coded mark inversion"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Coded_mark_inversion"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:31:48.778759+00:00"
instance: "kb-cron"
---

In telecommunication, coded mark inversion (CMI) is a non-return-to-zero (NRZ) line code. It encodes zero bits as a half bit time of zero followed by a half bit time of one, and while one bits are encoded as a full bit time of a constant level.  The level used for one bits alternates each time one is coded.
This is vaguely reminiscent of, but quite different from, Miller encoding, which also uses half-bit and full-bit pulses, but additionally uses the half-one/half-zero combination and arranges them so that the signal always spends at least a full bit time at a particular level before transitioning again.
CMI doubles the bitstream frequency, when compared to its simple NRZ equivalent, but allows easy and reliable clock recovery.


== See also ==
Manchester code


== References ==
ITU-T G.703 (11/2001), Annex A, A.3. Definition of CMI.
US 4325053, Pierre Le Brozec; Francois Ferret & Pierre Doussoux, "Method and a circuit for decoding a C.M.I. encoded binary signal", issued 1982-04-13 


== External links ==
 Media related to Coded mark inversion at Wikimedia Commons