ENVS 1200 Chapter 12: ENVS 1200 Chapter 12 Notes
13 May 2018
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ENVS 1200 Chapter 12 Notes – Summary
Introduction
• If the sequence of bits is long, the receiver may ultimately sample the wrong bit,
creating an error.
• In this illustration the timing difference is somewhat exaggerated, for clarity.
• There are a number of different ways of synchronizing the two systems.
• For modems, which transmit data one byte at a time, the solution is to provide clear
start and stop signals for the data and to resynchronize the timing between the
transmitter and receiver for each byte of data, so that the receiver knows exactly when
each bit is expected to occur.
• This approach is somewhat inefficient, because two extra bits (the start and stop
signals) must be sent for each byte of data.
• This technique is called asynchronous transmission.
• For longer bit sequences, the solution is to convert the data into a signaling method that
provides clocking as part of the data.
• Coside a sigalig ethod that say, geeates a → tasitio heee the it is a
one
• A → tansition whenever the bit is a zero.
• This technique guarantees at least one transition per bit of data sent through the
channel.
• The transitions can be used for clock synchronization.
• Look at the example
• The required transitions are shown as heavy arrows within the resulting waveform.
• Note that the fouth ad fifth its oth euie → tasitios.
• To accomplish this, there must be an additional downward transition to make the
seod → tasitio possile
• However the extra downward transition occurs between the data points and is ignored.
• This particular method is called Manchester encoding.
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