Manchester encoding is an encoding technique that synchronizes code with time. It is used in telecommunications and data storage. Computing code, as we know, comprises binary digits or bits, which comprise sets of zeroes and ones.

In Manchester encoding, zeroes correspond to lows while ones translate to highs. Synchronous clock encoding means the highs and lows are combined in one bitstream as they occur within the same amount of time. A bitstream or “binary sequence,” is simply a sequence of bits.

The Manchester code derives its name from its developers from the University of Manchester. They used the code to store data on the magnetic drums of the Manchester Mark 1 computer.

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Manchester encoding was widely used to record data on 1600 bpi computer tapes magnetically. It was also used in early Ethernet physical layer standards and remains utilized in consumer infrared (IR) protocols, radio frequency identification (RFID), and near-field communication (NFC).

What Is the Manchester Mark 1?

We mentioned the Manchester Mark 1 computer earlier. If you’re wondering what it is, know that it was one of the earliest stored-program computers, meaning it used a built-in application. Developed at the Victoria University of Manchester, England, its first version became operational by April 1949. Here’s a picture of the system:

Manchester Mark 1 computer
Source: https://upload.wikimedia.org/wikipedia/en/d/d8/Manchester_Mark2.jpg

What Are the Characteristics of Manchester Encoding?

The following characteristics are evident in Manchester encoding:

  • Each bit (0 or 1) is transmitted in fixed time.
  • A 1 is noted when high to low transition occurs.
  • 0 is expressed when a low to high transition is made.
  • The transition used to note 1 or 0 accurately occurs at the midpoint of a period.
  • Transitions at the start of a period don’t represent data.

Let’s dissect the characteristics using the following diagram.

Manchester encoding
Source: https://media.geeksforgeeks.org/wp-content/uploads/ETHERNET_1.jpg

In the diagram, you’ll see the time component in the first row. Notice that the bars are consistent, denoting fixed time. The second row shows the data that requires encoding. Note that bars going up translate to 1 (high) and those going down to 0 (low). When Manchester encoding is applied to the two components, the result is shown by either row 3 or 4. Finally, the change from high to low or vice versa always happens in line with time.

How Does Manchester Encoding Differ from Other Types of Coding?

Different encoding techniques are used to secure and quickly transmit data. These tactics include:

  • Non-return to zero level (NRZ-L): Voltage levels determine bit values. 1 represents a positive voltage, while 0 translates to a negative voltage.
  • Non-return to zero inverted (NRZ-I): Changes or lack thereof in voltage levels determine the bit values. 1 represents a change in the voltage level, and 0 means the lack of change.
  • 4B/5B encoding: 4 bits of code are mapped to 5 bits. It uses a minimum of 1 bit in each group or block. Data, in this case, gets transmitted in blocks.
  • 8B/6T encoding: 6 voltage levels represent 8 bits for a single signal, making this ideal for transmitting more data faster.

We already described how Manchester encoding is done above. It differs from the digital encoding techniques above because each data bit’s length is fixed by default. The bit state depends on the direction of every transition—high is 1 and low is 0.

Why Is Manchester Encoding Important?

Signaling synchronization is considered Manchester encoding’s primary advantage over other techniques. This synchronization allows higher reliability with the same data rate. Note, however, that Manchester encoding has downsides as well. Manchester-encoded signals, for instance, consume more bandwidth than the original signal.

As mentioned earlier, Manchester encoding transfers binary data based on analog, radio frequency (RF), optical, digital high-speed, and long-distance digital signals. Coding standards like Ethernet also use it.

In Ethernet, Manchester encoding describes how to represent binary ones and zeroes electrically. It is specifically used in all 10 Mbps Ethernet connections, such as 10BASE2 Thin Ethernet, 10BASE5 Thick Ethernet, and 10BASE-T Twisted-Pair Ethernet.

Manchester encoding, as we’ve seen, is critical to how Ethernet works and speeds up data transmission through telecommunication and computing devices.