Data Communications:Communication Industrial Networking

Wednesday, 10 July 2013

Data Communications

There are two main issue to consider in data communications:

1.the interface standard(e.g. the physical wiring & voltage consideration)
2.the software protocol(e.g. the order & type of characters being transmitted.

                                             

Format of Data Communication Message:

For a simple asynchoronous system such as RS232, it is common practice to send one character at a time.The format of a typical character frame is indicated in figure 1.1





                                     Figure :1.1 Format of a typical serial asynchronous Data character

Initially the data communications link is the idle state,lthe line is in the mark state,held to a constant negative voltage.

The parity bit included at the end of the character is effectively a fingerprint of the character to enable the receiver to identity whether any errors have occurred in the transmission. Example: even parity means that the total number of logic 1 bits in the data together with the associated parity bit must be an even number.
The optional settings for asynchronous transmission of characters are:

Start Bits       1
Data Bits        5,6,7,8
Parity Bits       even,odd,mark,space or none
stop Bits         1,2

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