The nRF21540 DK supports programming and debugging external
boards with nRF51 or nRF52 System on Chip (SoC)s. 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 detects the supply voltage of the board and program/debug the target chip on the external board instead of the onboard nRF52840 SoC.
Note: The voltage supported by external debugging/programming is VDD voltage. Normally, this is 3 V when running from
Universal Serial Bus (USB). But if the onboard nRF52840 SoC is supplied from either USB or lithium-ion (Li-ion) and the nRF power source switch (
SW9) is in either the Li-Po or USB position, then the VDD can be set by the nRF52840 firmware. Make sure the voltage level of the external board matches the VDD of the nRF21540 DK.
You can also use
P20 as a debug out connection to program shield-mounted targets. For both
P19 and
P20, the interface MCU detects the supply voltage on the mounted shield and program/debug the 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 nRF21540 DK can supply power through the Debug out connector (P19). To enable this, short solder bridge SB47.
Note: As long as SB47 is shorted, it is not possible to program the onboard nRF52840 SoC even if the external board is unplugged.