I am trying to follow the Linus getting started guide for the Colibri VF61 and Colibri evaluation board. I am having trouble in the section Basic UART usage. Following the instructions, I have jumpered UART-B Tx to Rx (connector X12 pin 17 to pin 16). I then execute the following commands:
stty -F /dev/ttyLP1 9600 -echo cat < /dev/ttyLP1 & echo "Testing UART" > /dev/ttyLP1
But I see no echo of the “Testing UART” string.
I noticed that the UART-B Tx and Rx signals were connected to both an RS232 tranceiver and an RS485 tranceiver on the evaluation board. I know they should both be disabled for the loop back to work, and I was not sure which jumpers would disable the transceivers. So I decided to remove the jumpers between X10 and X12 pins 16 and 17, and jumper X10 pin 17 to pin 16 for the loop back. It still does not work.
I should also note that when I execute the command:
cat < /dev/ttyLP1 &
I see something like this on the terminal:
And each time I execute that command the numbers seem to increment. Finally I decided to remove the loop back jumper and attach an oscilloscope to the UART-B Tx pin. I used echo “string” > /dev/ttyLP1 (with a long text string and ttyLP1 set to a low baud rate), but I verified that no data was sent out the Tx data pin. The pin simply stayed at 3.3V.
Why doesn’t this simple UART demo work? Am I doing something wrong? I seem to be stuck at this point in my evaluation.