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Author Topic: UART at 1Mhz  (Read 1189 times)

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Offline VegaObscuraTopic starter

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UART at 1Mhz
« on: December 06, 2010, 01:47:09 AM »
A few weeks ago I decided to add UART functionality to my $50 bot.  In the process, I bricked my atmega8 because I didn't know what I was doing with the fuses (can't say I wasn't warned).  This time, instead of trying the same thing again, I'm wanting to try getting UART to work without changing the fuses.  I checked the atmega8 datasheet for baud rates at 1mhz, and saw that 4800 is possible at 1mhz with a low error percentage.  This is about 1/10 of the speed that admin mentioned he was using in the $50 UART tutorial.  What would be the result of using UART at that baud rate?  Does this just mean that the bot will not send data to hyperterminal as frequently?

Offline Graynomad

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Re: UART at 1Mhz
« Reply #1 on: December 06, 2010, 09:40:07 AM »
Quote
Does this just mean that the bot will not send data to hyperterminal as frequently?
Sort of, probably just as frequently but at a slower rate (if that makes sense), and you'll have to set HT (and anything else talking to your mega) for 4800bps.
« Last Edit: December 06, 2010, 11:03:32 PM by Graynomad »
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Offline Admin

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Re: UART at 1Mhz
« Reply #2 on: December 06, 2010, 09:09:42 PM »
Your robot is limited on what it can do when sending data (ie busy doing something else). So if it sends a lot of data very slowly, you can imagine the problems you'll have :P

4800bps is an ok speed for the $50 Robot, but it can be limiting for more advanced bots.

Offline cyberfish

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Re: UART at 1Mhz
« Reply #3 on: December 06, 2010, 10:56:35 PM »
By 1MHz I'm assuming you mean the internal oscillator?

To do any kind of serial communication, you really want to have an external crystal. Serial communication is surprisingly dependent on tight tolerance (frequency) and low jitter clock, both of which the internal oscillator is bad at.

At extremely low speed (4800) you MAY be able to get away with it if you are lucky...

Just get a crystal.

 


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