Data encoding RZ NRZ NRZI Manchester ...

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The relationship between encoding and synchronous asynchronous http://blog.csdn.net/brucexu1978/article/details/6587487

Several common coding schemes: unipolar code, polarity code, bipolar code, Zero code, dual-phase code, non-zero code, Manchester code, differential Manchester code, multilevel encoding, 4B/5B encoding.

Excerpt

RZ encoding (Return-to-zero code), which is the zero encoding.

NRZ encoding (Non-return-to-zero code), not zero-encoded.

The difference between NRZI encoding (Non-return-to-zero inverted code) and NRZ is that NRZI uses a signal's flip to represent a logic, and the signal remains unchanged to represent another logic.

USB applies NRZI encoding when transferring packets.

A single reversal of the signal level represents 1, the level does not change to represent 0, and after a symbol is expressed, the voltage does not need to go back to 0

Non-zero coding is the most efficient encoding

The disadvantage is that there is a synchronization problem between the sender and the receiver

　　unipolar non-zero code , no voltage (that is, the yuan current) is used to denote "0", while the constant positive voltage is used to denote "1". The midpoint of each code element time is the sampling time, and the decision threshold is a half-amplitude level (i.e. 0.5). That is, the value of the received signal between 0.5 and 1.0, is sentenced to "1" code, if between O and 0.5 is sentenced to "0" code. The number of binary code elements sent per second is called the "code speed".

　　Bipolar does not return to zero code , "1" Code and "0" code all have current, but "1" code is positive current, "0" code is negative flow, positive and negative amplitude equal, so called bipolar code. At this time, the decision threshold is zero level, the receiver uses 0 judgment device or the positive and negative judgment device, the value of receiving signal if above 0 level is positive, sentenced to "1" code, if the 0 level below is negative, sentenced to "0" code.

Both of these codes emit or do not emit current (unipolar) over the full time of a single element, and emit positive or negative currents (bipolar). Each encoding occupies the width of all the code elements, so the two encodings belong to the full-width code, also known as non-zero code NRZ (Non Return zeros). If the "1" code is sent repeatedly, it is bound to send positive current continuously, if repeated sending "0" code, it is bound to continuously not send current or continuously send negative current, so that there is no gap between a bit code element and its next bit, it is difficult to distinguish between the identification. Zeroing the code can improve the situation.