ASYNCHRONOUS AND SYNCHRONOUS TRANSMISSION

Asynchronous Transmission

• it is a character oriented in nature and charcters from 5 to 8 bits are used.

How it works?

   When computers are transmitting one character at a time the arrival of the data at the other end of the communications link will be erratic or unexpected. In such case, the receiver doesn't automatically have a timing point at which to sample the waveform to decide whether the bit is 0 or 1.
    So a start-bit needs to be added to each byte to alert the receiver to the arrival of the information. The start bit therefore warns the computer of the arrival of a byte and provides a timing mark for the sampling. Once the edge of the start bit has been detected and the timer is running, the start bit is then ignored. The Stop bit is nothing more than a minimum period of time fot the system to reset, waiting for the next byte.
    Since the line is generally held high state when not in use, so the start bit is normally logic 0 and the stop bit is normally logic 1.

SYNCHRONOUS TRANSMISSION

• Data transmission in which time of occurenec of each signal representing a bit is related to a fixed time frame.

                                                                     Syn                     Control                        Data              Control
                                                                     Characters        Characters                 Characters     Characters

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