is used in Ethernet
to send data through the cable. It is a digital signal scheme that helps to reduce errors.
Manchester Encoding is a form of State-Transition Encoding (STE). Basically, the actual changing of the state from a signal, from a low (0 Volts) to a high voltage (+3 or +5 Volts) or from a high to low voltage. Manchester Encoding can also be classified as a type of Biphase coding.
Data 0 1 0 1 1 1 0 0
__ _____ ___ ___ ____
| | | | || || | ||
| | | | || || | ||
|____| |___| || || |___||___
Time 0 1 2 3 4 5 6 7 8
To set a digital 0, the signal must transition from high to low. To set a digital 1, the signal must transition from low to high. These state changes occur just before the bit is set in the device. It is the actual change of the state of the voltage that creates the digital value.
In the above example:
- For the first data bit at time 1, the signal is transitioning from high to low just before the time mark is reached, therefore at time 1 the digital bit is a zero.
- For the second bit at time 2, the signal transitions from low to high. Therefore, the data is a digital 1.
- For the third bit, at time 3, the signal is transitioning from high to low, therefore at time 1 the digital bit is a zero.
- For the fifth bit at time 4, the signal transitions from low to high. Therefore, the data is a digital 1.
- This is the one that sometimes confuses people. To create another digital 1, the signal must transition from low to high just before the time mark. Therefore, the signal goes low and then immediately goes back high. This last transition creates the digital 1 at time 5.
- Same as above.
- The signal transitions from high to low and stays there, creating a digital 0 at time 7.
- This is similar to creating consecutive 1's. To create another digital 0, the state must transition from high to low. The signal goes high then immediately low, which creates a digital 0 again because the state goes from high to low.
Manchester Encoding is used in a lot of electronics besides Ethernet. It is also used in military communications and data signaling.