STM32 Discovery board and fractional baud rate

[djackson]

Posted on March 14, 2014 at 17:11

I have the STM32F4 Discovery board (STM32F407 MCU) and was wondering if it is possible to enable fractional baud rates on this board.  I'd like to get a UART input rate of 100000 baud.

[waclawek.jan]

Posted on March 14, 2014 at 17:30

Why would that depend on the *board* rather than on the *chip*?

The answer is yes, but whether your particular baudrate is achievable and practical (i.e. error small enough) depends on the respective APB clock. Review RM0090 chapter 30.3.4. JW

[Tesla DeLorean]

Posted on March 14, 2014 at 17:47

It uses the fractional mode all the time, basically you divide the APB clock by (baud * 16) and by happenstance you both need a x16 clock, and there are 4-bits for the fractional setting.

So with a 42 MHz APB, write 420 in the BRR for 100000 baud

[djackson]

Posted on March 14, 2014 at 17:55

Good point on the chip vs the board. I wasn't sure what rates the APB clock could do.  I'll keep pulling documents and checking.

[djackson]

Posted on March 14, 2014 at 17:56

Perfect!  This should get me up and running right away.  Thank you.