Editing Manchester code (section)

==Encoding and decoding==
[[Image:Manchester encoding both conventions.svg|class=skin-invert-image|thumb|650px|An example of Manchester encoding showing both [[Manchester code#Conventions for representation of data|conventions for representation of data]], where : {{math|1=''[[Leet|1337]]''<sub>10</sub> = ''10100111001''<sub>2</sub>}}]]

Manchester code always has a transition at the middle of each bit period and may (depending on the information to be transmitted) have a transition at the start of the period also. The direction of the mid-bit transition indicates the data. Transitions at the period boundaries do not carry information.  They exist only to place the signal in the correct state to allow the mid-bit transition.

===Conventions for representation of data===
There are two opposing conventions for the representations of data.

The first of these was first published by G. E. Thomas in 1949 and is followed by numerous authors (e.g., [[Andy Tanenbaum]]).<ref name="tanenbaum">{{cite book |author-last=Tanenbaum |author-first=Andrew S. |author-link=Andrew S. Tanenbaum |title=Computer Networks |edition=4th |publisher=[[Prentice Hall]] |date=2002 |pages=[https://archive.org/details/computernetworks00tane_2/page/274 274–275] |isbn=0-13-066102-3 |url=https://archive.org/details/computernetworks00tane_2/page/274 }}</ref> It specifies that for a 0 bit the signal levels will be low–high (assuming an amplitude physical encoding of the data) – with a low level in the first half of the bit period, and a high level in the second half. For a 1 bit the signal levels will be high–low. This is also known as Manchester II or Biphase-L code.

The second convention is also followed by numerous authors (e.g., [[William Stallings]])<ref name="stallings">{{cite book |author-last=Stallings |author-first=William |author-link=William Stallings |title=Data and Computer Communications |edition=7th |publisher=[[Prentice Hall]] |date=2004 |pages=[https://archive.org/details/datacomputercomm00stal_1/page/137 137–138] |isbn=0-13-100681-9 |url=https://archive.org/details/datacomputercomm00stal_1/page/137 }}</ref> as well as by [[IEEE 802.4]] (token bus) and lower speed versions of [[IEEE 802.3]] (Ethernet) standards. It states that a logic 0 is represented by a high–low signal sequence and a logic 1 is represented by a low–high signal sequence.

If a Manchester encoded signal is inverted in communication, it is transformed from one convention to the other. This ambiguity can be overcome by using [[differential Manchester encoding]].

===Decoding===
The existence of guaranteed transitions allows the signal to be self-clocking, and also allows the receiver to align correctly; the receiver can identify if it is misaligned by half a bit period, as there will no longer always be a transition during each bit period. The price of these benefits is a doubling of the bandwidth requirement compared to simpler [[non-return-to-zero|NRZ]] coding schemes.

===Encoding===
{| class="wikitable" style="text-align:center;"
|+Encoding data using [[exclusive or]] logic (802.3 convention)<ref>{{citation |url=https://www.maximintegrated.com/en/app-notes/index.mvp/id/3435 |title=Manchester Data Encoding for Radio Communications |access-date=2018-05-28}}</ref>
|-
! Original data
!
! Clock
!
! Manchester value
|-
| rowspan=2 | 0
| rowspan=4 | XOR <br />⊕
| 0
| rowspan=4 | =
| 0
|-
| 1 || 1
|-
| rowspan=2 | 1
| 0 || 1
|-
| 1 || 0
|}

Encoding conventions are as follows:
* Each bit is transmitted in a fixed time (the period).
* A <code>0</code> is expressed by a low-to-high transition, a <code>1</code> by high-to-low transition (according to G. E. Thomas's convention – in the IEEE 802.3 convention, the reverse is true).<ref name="Manchesterencoding">{{Cite journal |author-last1=Forster |author-first1=R. |title=Manchester encoding: Opposing definitions resolved |doi=10.1049/esej:20000609 |journal=Engineering Science & Education Journal |volume=9 |issue=6 |pages=278–280 |date=2000|doi-broken-date=7 December 2024 }}</ref>
* The transitions which signify <code>0</code> or <code>1</code> occur at the midpoint of a period.
* Transitions at the start of a period are overhead and don't signify data.