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Manchester Encoding

Manchester Encoding

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  • 1. Manchester Encoding Theory and Use By Professor Tom Mavroidis January 31,2001
  • 2. What is Manchester Encoding ?
    • It is a process by which a Synchronous clock encoding technique is used by the OSI physical Layer to encode the clock and data of a synchronous bit stream.
  • 3. What is the difference?
    • In this technique the binary data to be transmitted over the cable are not sent as a sequence of logical 1 & 0’s known as non return to zero (NRZ), instead the bit are translated into a different format that has a number of advantages over using straight binary.
  • 4. Where is it used?
    • A popular technique used for encoding data on magnetic disks.
    • Also known as phase encoding
    • Problems include poor bit storage density
  • 5. Resides in the Physical Layer
    • Physical Layer serializes the frame (converts it to a series of bits) and send it across a circuit to the destination.
  • 6. Three types of encoding discussed
    • NRZ - Non Return to Zero
    • RZ - Return to zero
    • Manchester encoding
  • 7. NRZ , Non Return to Zero transmission
    • Each data bit is represented by a level. High = logic 1 low = logic 0
  • 8. Problem with NRZ
    • Long runs of consecutive bits with the same value make it impossible to detect bit boundaries by the inability of the receiver to detect the clocking speed.
  • 9. RZ - Return to zero
    • Pulses used to represent bits
    • logic 1 = pulse logic 0 absence of pulse
  • 10. RZ - Advantages
    • Clock signals can be extracted from the logic 1 signals.
    • Halves the width of the pulse
    • Polar RZ sends pulses for both logic 0 and logic 1
    • Requires an extra voltage level
  • 11. Manchester Encoding
    • Logic 1 is represented by a transition in a particular direction in the center of each bit.
    • Opposite direction used to represent logic 0
  • 12. Representation
    • Logic 0 1 to 0 (downward transition at bit center)
    • Logic 1 0 to 1 (upward transition at bit center)
  • 13. Manchester Encoding
    • Was named after its birthplace in Manchester, England
    • Bit transitions do not always occur at the ‘bit boundaries.
    • There is always a transition at the center of the bit
  • 14. Improved clocking
    • Allows the receiver to extract the clock signal
    • Correctly decodes the value and timing of each bit
  • 15. Receiver
    • Reassembles the series of bits to form a frame and forwards the frame for processing by the link layer
    • Frame is then CRC checked and a retransmission is requested if the checksum is invalid.
  • 16. Representation of phase shift
  • 17. Uses
    • Manchester encoding is used to :
    • Transmit data across systems
    • Store data on magnetic media, disks etc.
    • Communicate with Satellites
  • 18. Conclusion
    • Based on application different types of encoding can be used
    • Manchester encoding exhibits poor bit storage density but improved reliability.
  • 19. Links
    • http://www.erg.abdn.ac.uk/users/gorry/course/phy-pages/man.html
    • http://home.europa.com/~celiac/manch_enc.html
    • http://csshaun.cs.ru/ac/za/netnotes/netnotes003.html
    • http://www.pdp8.net/tu56/tu56.shtml