Friday, March 1, 2019

FMA Unit 4.3 Serial Transmission format


B.   Serial Transmission format
1   1.  Asynchronous Data Transfer
     



·        It is “Character” oriented data transfer.
·        One data bit is transferred at a time.
·   When data is not transferred the output line of transmitter is High i.e. Marking State.
·  The start of data is indicated by a low start bit, which is used to synchronized transmitter and receiver. After the start bit, data bits are transfer serially.
·     The data bits are followed by a one or more high stop bits. After the stop bits same logical level is maintained on output lines.
·      The receiver will check for marking state. When it detects low on data line then it is treated as valid start bit.
·       After start bit receiver will start accepting data bits D0 to D7. At the end it will check stop bits and go back to initial marking state.
·        The asynchronous data transfer format consists of a start bit, data bits and stop bits called as Frame.
·   The clock to both transmitter and receiver are separate. But operating frequency for both is maintained same.






 2.  Synchronous Data Transfer




·        It is “Block of data” oriented data transfer.
·        The block of data bytes transferred serially one after the other.
·    Before sending data, special characters are transferred by transmitter to receiver to achieve synchronization between transmitter and receiver. This special character called as Sync Character.
·  To start transmission, the Sync Character bits are sent by transmitter followed by data bits.
·   When data is not transferred the output line of transmitter is High i.e. Marking State.
·     The receiver will go on checking input lines; and comparing whatever data received with Sync Character.
·     When match occurs then it is consider as the receiver is in synchronization with transmitter.
·      When the receiver is synchronized, then it will go on accepting data bits in the same sequence.
·     The clock of both transmitter and receiver is same to avoid wrong data bits.



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