how to view uart logs while debug out external board through nRF52 DK?

[kfcube]

nRF52DK

p20 debug out

external board is 51822 + sensors

I managed to connect the external board through p20 on the 52DK. I can successfully program the external board. I tried to view the uart logs through the 52DK. I connect the TX, RX of the external board to P0.06, p0.08, mapped as following: 

TX(external board) -- P0.06 (52DK)

RX(external board) - P0.08 (52DK)

I disabled the Flow control while init uart.

Then I connect the uart on my PC using screen: screen /dev/tty.usb...  115200

However, I couldn't see any logs output. I tried several times to re-program, nothing happend.

Can you please suggest me how to do? 

Thanks,

[kfcube]

I have got this work - just connect rx tx it works fine. There were something wrong on my code that went wrong before enter into the uart part.