How to use nrf5340-DK to display uart from nrf52480dongle ?

[HoangDuong]

I using nrf5340-DK to program nrf52480 dongle with basic hello world sample. i cant get message from UART_TX on pin P0.20 of dongle to CoolTerm virtual com port by using USB_UART bridge. Hardware wire like this:

nrf52840dongle	USB_UART bridge
P0.20/TX	RX pin
P0.24/RX	TX pin

But i dont want to use external USB_UART bridge, i want to use nrf5340 to get UART message from nrf52840. 

According to this info: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_nrf5340_dk%2FUG%2Fdk%2Fvir_com_port.html&cp=3_0_4_2_1

I can use P0.20 of nrf5340-DK connect to P0.20 of dongle and use the second virtual COM of nrf5340-DK.

But i get nothing. 

How can i use virtual com port of nrf5340-DK to get UART_TX from nrf52840dongle like nrf5340 MCU on DK.

ps:

1 - the VDD out of dongle is 2.97 same with VDD_nRF of nrf5340-DK 

2 - the nrf5340 MCU only blink led and do not using printk function. 

Edit: my typo mistake, UART_TX pin in nrf52840dongle is P0.20 

[Hieu]

Hi Hoang,

That is an interesting idea you came up with. It made me feels dumb for roaming the office looking for a USB-UART bridge two months ago when I have a few tens of DKs around me.

I checked your idea with this setup:

nRF52DK P0.06           connects to     nRF5340DK P0.20
nRF5340DK Debug Out     connects to     nRF52840DK Debug In

nRF52DK running an application that prints out a lot continously on P0.06
nRF5340DK is erased

It works for me. I can debug the nRF52840 chip with my nRF5340DK debugger and see VCOM1 of the nRF5340DK prints out my nRF52DK log.

Can you try again with the nRF5340 erased? Or at least make sure that whatever is running on the nRF5340 chip keeps pin P0.20 floating? Even though you are not printing, a peripheral could be controlling the pin, and pull it low/high, and make communication impossible.

Another thing to check is whether you are connected to the correct port by "the second virtual COM" or not.
The nRF5340DK Rev 1.0.0 has three working VCOM ports and Rev 2.0.0 has two.
They don't show up in the same order on every computer. You can use nrfjprog or the VS Code Extension to check what is VCOM1, which should be connected to P0.20.
Or you can just circle around your ports to see which one is printing things, but that depends on the assumption that the setup works.

Hieu

[HoangDuong]

Hieu said:

Can you try again with the nRF5340 erased?

Yes, that was problem, I try:

nrfjprog --family nRF53 --eraseall

then all thing work well. It was cost me a week before post question on nordic devzone.

Thanks for support