encountering an issue while trying to program the Fanstel BT840F module using the nRF52840 DK

[Clarity]

I have two boards:

1. nRF52840 DK (which has a faulty buck converter, so I am powering it via USB).

2. Fanstel BT840F board, which provides power to the Debug In connector of the nRF52840 DK.

When connecting the Debug In interface, both the nRF52840 DK and the BT840F board get programmed simultaneously. This is not an issue.

However, when I try to program an independent BT840F module (not the full board), it does not get programmed. My wiring is as follows:

Wiring Between nRF52840 DK and BT840F Module

nRF52840 DK	BT840F Module
VDD	VDD
GND	GND
SWDIO	SWDIO
SWCLK	SWCLK

Despite this setup, the module is not responding to programming. Could you please assist in troubleshooting this issue?

[Kenneth]

Hello,

If you want to program an external module, you should use the debug out (P19) from the DK to the external board. You also need to connect pin #3 (SWD0_SELECT) to ground on the external board, as described here:
RE: nrf52840 DK description and schematic do not agree for external debug port P19 

Kenneth

[Clarity]

when connecting the SWD0_SELECT pin to ground on the external board and connecting the Debug connector to the Debug out. When these connections are made, the Vdd supply on the DK board starts fluctuating.

[Kenneth]

If the Fanstel module is self powered, then you can disconnect the VDD pin. Only make sure the voltage level is about the same (~3V).

Kenneth

[Clarity]

I’m noticing that the Vdd supply fluctuates when I power up the DK board using the MCU USB connection, without involving the FANSTEL board. Could this be a sign of a problem with the buck converter?

[Kenneth]

Define fluctuate? Have you modified the DK in any way?

Kenneth