Manchester encoding and differential Manchester encoding

        Digital signal encoding is to solve the problem of digital signal representation of digital data, that is, to express data by encoding digital signals. The work of digital signal encoding is generally completed by hardware, and there are three commonly used encoding methods: non-return-to-zero code, Manchester encoding, and differential Manchester encoding.

         Differential Manchester encoding is an encoding scheme that uses mid-position transitions for timing. Data is represented by adding a transition at the beginning of the data bit. The Token Ring LAN uses the differential Manchester coding scheme.
There is a level transition in the middle of each clock cycle, and this transition is used for synchronization. At the beginning of each clock cycle: a transition means that the bit is 0, and no transition means that the bit is 1.

The advantage of the differential Manchester encoding is: the sender and receiver can maintain synchronization according to the clock signal that comes with the encoding, and there is no need to specifically transmit the synchronization signal, so the cost is low; the disadvantage is: the implementation technology is complicated.

        Manchester encoding (Manchester Encoding), also called a phase encode (PE), is a synchronous clock encoding technique used to encode the physical layer of a synchronous clock and data bit stream. Manchester encoding is used in the Ethernet media system. Manchester encoding provides a simple way to encode simple binary sequences without long periods and no conversion levels, thus preventing loss of clock synchronization or analog link bit errors from low frequency shifts in poor compensation. Under this technology, the actual binary data is transmitted through the cable, not as a sequence of logic 1 or 0 (technically called reverse non-return-to-zero (NRZ)). On the contrary, these bits are converted to a slightly different format, which has many advantages by using direct binary encoding.
　　Manchester encoding, often used for LAN transmission. In Manchester encoding, there is a transition in the middle of each bit, and the transition in the middle of the bit is used as both a clock signal and a data signal; a transition from high to low means "0", and a transition from low to high means "1" . There is also a differential Manchester encoding. The transition between each bit only provides clock timing, and whether there is a transition at the beginning of each bit is used to indicate "0" or "1", with a transition to "0", and no transition to "1".

The coding rule of Manchester encoding is: the level transition from low to high in the signal bit indicates 1, and the level transition from high to low in the signal bit indicates 0.

 

Means 1 0 1 1 0 0 1

 Standard Manchester encoding waveform Figure 1 represents from high to low, 0 represents from low to high

 Differential Manchester encoding waveform Figure 1 represents no transition (that is, the previous waveform is high and continues to start at high, and the previous waveform is low and continues to start at low). 0 represents a transition (that is, the previous waveform). The waveform in the high position must now be changed to start at low, and the last waveform in the high position must be changed to start at low)

Differential Manchester encoding: the first one is 0 from low to high, the first one is 1 from high to low, the latter depends on whether there is a jump to determine