An article for you to understand - Manchester code

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Let me write it out front

1 what？ What is Manchester code

 2 how？ How to use Manchester code

2.1 The code of Manchester ：

2.2  Decoding of Manchester ：

3 why？ Why recommend Manchester code ? The advantages and disadvantages of this coding method

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Let me write it out front

         Why encode data before data transmission ？

         That's a good question ！！

         In a word ： Make the transmission system have certain error correction ability and anti-interference ability , The bit error rate of code stream transmission can be avoided to the greatest extent ！

1 what？ What is Manchester code

         Manchester coding is also called phase coding , It is a synchronous clock coding technology . It is expressed by high-low conversion of level “0” or “1”, There is a jumping action in the middle of each person , This action is a clock signal , It also makes data signal , But because each symbol is adjusted to two levels , Therefore, the data transmission rate is only half of the modulation rate 1/2, Its coding efficiency is 50%. Commonly used for LAN transmission ！

         Representation ：

                 The first one is G. E. Thomas, Andrew S. Tanenbaum1949 Put forward in ：

                         Bit intermediate level From low to high Jump representation "0".

                         Bit intermediate level From high to low Jump representation "1";

                 The second kind IEEE 802.4( Token bus ) And the low-speed version IEEE 802.3( Ethernet ) Specified in the ：

                         Bit intermediate level From low to high Jump representation "1".

                         Bit intermediate level From high to low Jump representation "0";

         For the above agreement , How to use , It needs to be distinguished according to the actual application scenario . So is there a coding method that can avoid the possible ambiguity caused by the above two conventions ？ Of course there is , Differential Manchester code . To avoid confusion , It will be described in a separate article ！ It's best to read this article carefully first , Let's go to Manchester again ！

 2 how？ How to use Manchester code

         Manchester code is binary data through level jump “0” and “1” Coded , For which level jump corresponds to which data , There are actually two different data conventions ： That is, the two representations mentioned above . in application , Unless otherwise specified , The coding rules of Manchester code adopt the second convention .

2.1 The code of Manchester ：

         Manchester code is used “01” and “10” To represent “1”” and “0” Of , Therefore, in the actual circuit design , We can pick one 2 choose 1 Digital selector to complete this function .

2.2  Decoding of Manchester ：

        （ This part is also commonly used in the decoding logic of other coding methods , For example, the wheel speed of automobile electronic clock AK Transfer protocol , The data information part is encoded by Manchester , For its decoding logic , The same applies ）

         The purpose of Manchester decoding circuit design , How to accurately extract from the code stream of Manchester code “10” and “01” The signal , And convert it into “0” and “1”.

         For example, for Manchester yards “01010101”, If you start decoding from the first , The resulting binary code is “1111”, And if you start decoding from the second bit , The resulting binary code is “000” And two Manchester yards at the head and tail .

         thus it can be seen , If there is only “1” or “0” You can't get the correct decoding result , If... Appears in the Manchester encoded data stream “00”, be “00” The symbols before and after must be “1”; If... Appears in the Manchester encoded data stream “11”, be “00” The symbols before and after must be “0”, therefore , We can “00” And “11” As the flag bit of Manchester code decoding .

         In the actual design circuit , A buffer can be used , Save the signal collected by the previous clock and the signal collected by the current clock , When the contents of the buffer are “01” when , Output “1”; When the contents of the buffer are “10” when , Output “0”; When the contents of the buffer are “00” or “11” when , The output remains unchanged .

3 why？ Why recommend Manchester code ? The advantages and disadvantages of this coding method

         This problem , It belongs to an open question , Advantages and disadvantages , All need reference and comparison . The content listed by bloggers is incomplete , In the process of using , You can also talk about the pain points and convenience points of use ！

         advantage ：

        1 Jump level transmits synchronous clock information , There is no need for a separate clock synchronization signal , Excluding DC component , It has good anti-interference ability , More suitable for channel transmission .

         shortcoming ：

        1 Low coding efficiency , The data transmission rate is only of the signal rate 1/2.