nRF52840 dongle UART application only works on "older" batch of dongles.

Question

Dear Nordic Team, 
 I recently ported the BLE UART example project for the PCA10056 to the PCA10059 dongle (SoftDevice 113). I added some minor changes like RX/TX pins, GPIO config for an additional button and some special character escaping to trigger LEDs. 
 Everything works as expected with my "old" dongle: 
 
 Revision: 1.2.0 
 Date: 2020.7

I flashed the exact same binary to the "new" dongle I recently ordered. 
 
 Revision1.2.0 
 Date: 2020.19 
 
 Here the application shows an erratic behavior: Data received via BLE RX is not forwarded to UART TX, and data received by UART RX is not forwared to BLE TX. Instead, everything received by UART RX is directly "looped back" to UART TX. 
 I'm really lost here, since I cannot debug the application on the dongle. Plus I would expect the same binary to behave the same on a device with the same Revision. 
 Many thanks for your help! 
 Marc

Simonr · Accepted Answer

Hi again Marc 
 A light bulb just lit above my head as I was writing you a reply. The P0.09 and P0.10 are by default used as NFC pins on the nRF52840 and are restricted to standard drive/low frequencies only. This doesn't explain why your 2020.7 Dongle works as intended, but it explains why the others don't if you haven't configured the NFC pins as GPIOs. If you add the preprocessor define "CONFIG_NFCT_PINS_AS_GPIOS" (add under project settings -> "Preprocessor" -> "Preprocessor definitions"), you should be able to use these NFC pins as normal GPIOs. You can alternatively use any other pins on the Dongle as TX and RX pins to see if it works as intended there (P0.13 and P0.15 for instance). 
 If you've already thought of this and configured the NFC pins as GPIOs from the beginning, then yes please, if you could send me the binary or .hex file of your project I can do a test on my end. I have a 2020.7 and a 2020.37 myself that I have not been able to reproduce the issue on. I'll solder those pins as well and test on my end. 
 Best regards, 
 Simon