Tuesday, January 13, 2009

Understanding Baud Rate and Framing Errors

As all we know that sending and receiving hardware are agreed on the length of the time the voltage will be held for each bit.Instead of specifying the time per bit,which is a small fraction of second,communication systems specify the number of bits that can be transferred in a second.For ex:some early RS-232 connections operated at 300 bits per second,19200 bits per second and 33600 bits per second are more common.Technically ,transmission hardware is rated in baud,the number of changes in the signal per second that the hardware generated.For the simple RS-232 scheme presented, the baud rate is exactly equal to the number of bits per second.Thus,9600 baud means 9600 bits per second.

To make RS-232 hardware more general,manufacturers usually design each piece of hardware to operate at variety of baud rates.The baud rate can be configured either manually by physically setting switches on the hardware when it is installed in a computer or automatically by device driver software in a computer.If the sending and receiving hardware are not configured to use the same baud rate,errors will occur because the receiver's timer will not wait an appropriate length of time for each bit.To detect errors,a receiver's measure the voltage for each bit multiple times and compares the measurements.If the voltage do not all agree or if the stop bit does not occur exactly at the time expected,the receiver reports an error.Such errors are known as framing errors.

No comments: