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PICList Thread
'[PIC]: usart autobaud routine'
2001\04\24@014931 by Vasile Surducan

This damn colon...

On Mon, 23 Apr 2001, Vasile Surducan wrote:

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2001\04\24@024800 by Bill Westfield

face picon face
> I'm trying to implement an autobaud usart routine. My ideea was to change
> the spbrg value register if a frameerror occure. The result is
> interesting. It work's ok if I switch only from 57600 baud to 19200 baud
> but if I want to use more than two different baud rate ( ie: 57600, 19200,
> 9600, 4800, 2400, 1200 ) by counting how many frameerrors appears and
> change spbrg value (and brgh if necessary ) does not work.

So you intend to change bit rate, and then again if you get another framing
error, and so on, nominally taking N keypresses to step through N possible

I think you're missing the fact that if you run your UART at 57600bps, and
send it a character at 9600, you could get SIX or so framing errors.
Somehow you need to wait for all of the "noise" data generated by a single
keypress to settle down before you start looking at the next character.

On something like a PIC, I'd be very tempted to switch the uart rxd pin
into a programmed input, and measure the length of the shortest "pulse"
seen during a character, and then calculate the bitrate from that.


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