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why devide by 32 while calcluting baudrate in 8051

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Author
projesh naik
Posted
17-Dec-2009 09:53 GMT
Toolset
C51
New! why devide by 32 while calcluting baudrate in 8051

Hi ,
I want to know why we will divide by 32 while calculating baud rate in 8051. plz reply to my id..

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Author
Jon Ward
Posted
17-Dec-2009 15:43 GMT
Toolset
C51
New! RE: why devide by 32 while calcluting baudrate in 8051

Because, that's the way it is. Same answer for why are there 24 hours in a day.

Jon

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Author
Per Westermark
Posted
18-Dec-2009 00:22 GMT
Toolset
C51
New! RE: why devide by 32 while calcluting baudrate in 8051

The important thing is that a UART needs a clock frequency that is several times faster than the baudrate.

This allows the UART to support a mismatch in baudrate between sender and receiver.

The UART samples again and again until it detects the start of the start bit. Then it keeps counting n clocks / bit until having taken care of the stop bits.

While counting the clocks, the UART takes a couple of samples within each bit window and uses a majority vote to determine if the bit was a zero or a one, improving noise handling.

And by ignoring the start and end of each bit window, the UART can handle that the bit window slowly glides forward or backward because of smaller baudrate errors.

If looking generally at UARTs, it is common that the UART samples 16 times faster than the baudrate. Some may sample faster and a few lower-quality UART may sample slower.

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Author
Andy Neil
Posted
18-Dec-2009 00:46 GMT
Toolset
C51
New! How the 8051 UART works...

... is described in the so-called "bible" for the 8051.

Links here: http://www.8052.com/faqs/120112

See also: http://www.8052.com/tutorial

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Author
projesh naik
Posted
18-Dec-2009 03:59 GMT
Toolset
C51
New! RE: why devide by 32 while calcluting baudrate in 8051

Thank you

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Author
Andy Neil
Posted
18-Dec-2009 06:44 GMT
Toolset
C51
New! RE: why devide by 32 while calcluting baudrate in 8051

You got this forfree - how about sharing it with the rest of your class: http://www.keil.com/forum/docs/thread16119.asp

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