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Stellaris® ARM® Microcontrollers
Stellaris® ARM® LM3S Microcontrollers Forum
We set the LM3S9D92 UART1 as standard RS232 for communication, but find some baudrate are offset some from the value we set.
And we do some calcuation and detection as follows:
Does the offset is normal or not?
If normal, could you give me some reference data?
If not, could you tell me why? Or introduce some FAE in Shenzhen, China to contact us?
We are looking forwared for your reply!
To my knowledge, there should not be any offsets to the actual UART baud rate other than those caused by the fractional divider. Can you go into more detail concerning your process for measuring the baud via oscilloscope? It's been a bit of time since I've scoped out a UART line, but my experience has been that it tends to be very close to the calculated offset. I would be interested in taking some measurements myself to verify what you are saying, but I'd like to follow the same procedure for measurement as you are currently using.
I had an additional question about the table of data that you posted as well: I'm not certain what you mean in the last column, that you have labeled "One byte last bit error(%)." Could you go into detail as to what you mean by this?
Also, I'm curious about your intended use for this UART. It was my understanding that most RS232 devices had a tolerance of around 2 or 3%. With the exception of the results you saw on the 1200 baud rate, it seems like the deviations you're observing would be well within that range.
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