Connecting Serial Port without USB on nRF52840DK

[Mehmet C.]

Hi All,

I have a nRF52840DK and looking for a solution to connect the VCOM serial port to the PC, without using USB. I will need to connect the serial port to another board which doesn't have a USB input.

According to the documentation, nRF52840 UART pinouts are placed at P0.05, 6, 7 and 8 for RTS, TXD, CTS and RXD respectively.

If I connect the dev. kit to the computer using USB, everything works without problem but if I connect these pins to the serial port of my computer, I cannot communicate. 

I've tried playing around with the switches on the DK but no success.

Is there a way to connect the nRF52840DK VCOM to the computer serial port (or any serial port) without using USB?

Thank you,

[Einar Thorsrud]

Hi,

The default GPIO pins used for UART on the DK are connected to the onboard debugger and not the GPIO header when the debugger is active (you can see this on the explanation printed on the back of the DK PCB). To use the UART with another device you need to select other GPIO pins and configure our firmware to use those instead.

Regarding FW, if you use the nRF5 SDK we can use the UART example as reference. That use the pins specified in the board file, so you would have to change those in components/boards/pca10056.h. If you are using the nRF Connect SDK you can specify other pins in an overlay file, as shown here.

[Mehmet C.]

Thank you for the answer. 

> The default GPIO pins used for UART on the DK are connected to the onboard debugger

I thought there would be a jumper connection to override this and connect the output to the GPIO header.

> you need to select other GPIO pins

This might work. I couldn't find any information on this but can I use any GPIO pins for this purpose? Or is there a specific pins I would need to use?

[Einar Thorsrud]

You can use any GPIO as long as it is available, though it is a good idea to avoid GPIOs that are close to the radio to avoid causing noise for the radio (those ar marked with "low frequency I/O only" in the pin assignments table).