UART using internal DCO

cuong nguyen1

Is there any way to do uart communication (around 9600 baud) using only an internal clock? I have very limited space on a board design and would like to eliminate the crystal if possible. I was looking into REFO (Internal REference, Low-Frequency Oscillator) but was wondering if there was any other method.

Any ideas will be appreciated,

Thanks

over 12 years ago

0 zrno soli over 12 years ago

Guru 34873 points

You can use DCO, and BR calculator...

http://forum.43oh.com/topic/2640-uart-configurator

0 old_cow_yellow over 12 years ago

Guru 58965 points

If the chip you use has REFO, you can use that for 9600 bps or lower. Some chips do not have REFO.

If the chip has "calibration constants" and you did not erase or over-write them, you can use them too. (Some chips do not have those.)

Some chips have factory trimmed DCO and that is accurate enough already.

0 cuong nguyen1 over 12 years ago in reply to old_cow_yellow

Intellectual 540 points

I am currently using MSP430 FRAM series which doesn't have REFO but does have a factory trimmed DCO. How do I find the baud rate error percentage for 9600 baud?

0 Brian Boorman over 12 years ago in reply to cuong nguyen1

Guru 25210 points

cuong nguyen1 said:

I am currently using MSP430 FRAM series which doesn't have REFO but does have a factory trimmed DCO. How do I find the baud rate error percentage for 9600 baud?

You look at the datasheet for your part and find out what the tolerance on the DCO is when calibrated. You take the min/max numbers, apply your BRG divisors, and look at the range of output frequencies. Divide those BRG min/max values by your desired BRG and multiply the results by 100 to get error percentage.

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UART using internal DCO