Error in adding Serial Cap RS-485 on BBB

Hello all,
I have two questions below. And please help.

  1. I add a RS323/RS485 Serial Cap from Logic Supply to my BBB.
    After I configured the rs485 cap, pinmux shows that the UART is connected to pins 28 and 29. (Pin 28 is pin 44e10870).
    But when I check the kernel log, I have Error -22 saying that pin 44e10870 is already requested by pin 481a8000.

  2. How do I test RS485 function? And what interface cable do I need?

Any ideas?

Best Regards.


Are you trying to load another overlay along with the CBB-Serial overlay? If you have the cape-CBB-Serial-r01.dtbo overlay in /lib/firmware and boot with the cape attached everything should already be muxed properly, and you should be able to use UART4 (/dev/ttyO4) for RS485.

The only RS485 connection point on the cape is the screw terminals, so you should just run a twisted pair of wires from an RS485 device to the connections on the terminal block labeled RS485A and RS485B.