nRF52840 Preview DK v0.9.x

Debug output

The nRF52840 Preview DK board supports programming and debugging external boards with nRF51 or nRF52 SoCs. To debug an external board with SEGGER J-Link OB IF, connect to the Debug out connector (P19) with a 10-pin cable.

Figure 1. Debug output connector

When the external board is powered, the interface MCU will detect the supply voltage of the board and program/debug the target chip on the external board instead of the on-board nRF52840 SoC.
Important: The voltage supported by external debugging/programming is the VDD voltage. Normally, this is 3 V when running from USB, but if the on-board nRF52840 is supplied from either USB or Li-ion, VDD can be set by the nRF52840 firmware. Make sure the voltage level of the external board matches the VDD of the nRF52840 Preview DK.
You can also use P20 as a debug out connection to program shield-mounted targets. As for the Debug out header (P19), the interface MCU will detect the supply voltage on the mounted shield and program/debug the shield target.

If the interface MCU detects target power on both P19 and P20, it will by default program/debug the target connected to P19.

If it is inconvenient to have a separate power supply on the external board, the nRF52840 Preview DK board can supply power through the Debug out connector (P19). To enable this, short solder bridge SB47. Note that as long as SB47 is shorted, it is not possible to program the onboard nRF52840 SoC even if the external board is unplugged.


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