frame, CMI line coding
In
telecommunication
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that ...
, coded mark inversion (CMI) is a
non-return-to-zero
In telecommunication, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negat ...
(NRZ)
line code
In telecommunication, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained ...
. It encodes ''zero''
bit
The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represente ...
s 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
pulse
In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the n ...
s, 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
In serial communication of digital data, clock recovery is the process of extracting timing information from a serial data stream itself, allowing the timing of the data in the stream to be accurately determined without separate clock information. ...
.
See also
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Manchester code
In telecommunication and data storage, Manchester code (also known as phase encoding, or PE) is a line code in which the encoding of each data bit is either low then high, or high then low, for equal time. It is a self-clocking signal with no D ...
References
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ITU-T
The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Co ...
G.703
G.703 is a 2016 ITU-T standard for encoding voice or data over digital carriers such as T1 and E1. G.703 provides specifications for pulse-code modulation (PCM).
G.703 also specifies E0 (64kbit/s). For information about E0 audio see G.711.
...
(11/2001), Annex A, A.3. ''Definition of CMI''.
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External links
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{{Bit-encoding
Encodings
Line codes
