Pin interface and factory programming nRF52840 over UART connected with processor

[pin2]

Hi,

I have arm based application processor and need to connect with nRF52840 using UART, I don't have any idea about bootloader and factory firmware when hardware assemble. 

1) What is pin connection required to connect with application processor to factory program nrf52840(new module without any firmware) via UART? without Seggar debugger/programmer.

2) If firmware flash is possible via UART, which pin required to put nRF52840  in booting mode?

3) Is DFU example is enough to  do factory firmware update which is given in SDK nRF5_SDK_15.0.0_a53641a?

Thanks

[RK]

1) there  is no pin connection available to program the module from the factory, you HAVE to use SWD to program it  with an initial image. If you wish to add a UART bootloader to your code so you can upgrade it that way later you're free to write that but there isn't one on the chip to start with. 

2) the chip has no built-in UART firmware update mode, so there is no pin to put it in 'booting' mode. 

3) DFU will let you upgrade the firmware over Bluetooth after it's been initially programmed but not from factory state. 

These aren't Atmel chips with a built-in serial bootloader. 

[pin2]

Thanks for quick response.

3)  If nRF52840 is with default bootloader before factory,  no softdevice and application, then can we do OTA using DFU via UART in this case RX,TX,CTS,RTS connection enough with application processor(arm based)?

[RK]

again no - the chip comes from the factory entirely blank it has NOTHING on it. You have to do the initial programming via SWD (or have the factory do it). 

And OTA means 'over the air' so you wouldn't do OTA via UART, you'd do OTA via bluetooth. And to do that you need to have first put a bootloader/softdevice etc on the chip via SWD.