Beagle Bone Black Serial UART Speed is Slow

Question

I am using the BBB and setting up UARTS one the I/O pins.

Example UART4, P9 pins 11 and 13.

I am set for 9600 baud

Im looking at teh bit patter on an oscilloscope and notice the serial speed comes out of the port at a rate slower than 9600 baud (about 7-8% slower)

That means that rate is outside of the acceptable speed tolerance of about 5% for the serial 9600 standard.

I cannot properly communicate with serial devices that use 9600 baud.

Any idea on the cause of this and if there is some sort of calibration that can be done to improve the accuracy of the UART.

I am using Debian operating system

To run the tests I am using minicom

Ken

gdstew · Answer

If the UART baud rate counter and the timer that supplies the UART clocks (4) are set correctly the baud rate should be within

0.16% at 9600 baud as specified by the TI AM335x Technical Reference Manual. I did some quick calculations on the values

given in the manual and they are correct. It would seem(?) that one of the two is not being set to the correct count value. As

far as I know it should be the Debian that sets these counter/timer values based on the baud rate requested by minicom. Since

these timers are all internal the only way to verify they are correct would be to read the timer count and UART divisor registers

after minicom has been started.

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