BBB How to link UART port on GPIO pins to a port dev


I am using P9.21 (SPIO_DO) and P9.20 (SPIO_SCLK) as UART port.
(BBB pins on Connector 9)

How to link these pins as a port to a tty device, say /dev/ttyS1, or even /dev/ttyS10?

so, ttyS1 or ttyS10 is opened, it is the uart port connected by P9.20/P9.21 pins.

Thank you,


Hi @dzhou, P9.20 doesn’t have a TX/RX mode just cts.

P9.21 can be uart2_txd, which can be loaded via this overlay:

Which should auto-configure as /dev/ttyS2 on startup…


Hi Robert,

Thank you very much.
UART2 is on P9.22.P9.21. It was my typo.

Best Regards,