nRF52 DK P20 debug out -- how do I know it is connected?

Question

Hi, 
 I am using the nRF52840 DK to connect to an external board via the P20 shield debug out. I was wondering if any indication is given if a board is connected correctly? 
 Currently I have: 
 on DK | on my PCB (nRF 52832) 
 VDD nRF --> 3.3V 
 SWD IO --> SWDIO 
 SWD CLK --> SWDCLK 
 and on the DK I have SWD SEL connected to the #2 pin VDD nRF 
 I believe the connections above will supply power to the chip on my PCB. 
 Anyways, I really want to know how I can check if the board is recognising my external chip! 
 Thanks

user14926 · Accepted Answer

Hi, 
 You need to connect VTG to the supply voltage of the external board (or to VDD on the DK if you are powering the external board from the DK). This is used by the debugger chip on the DK to determine which SWD interface should be used for programming (P19, P20, or to the onboard nRF5x chip). 
 There is no direct visual indication that the external board is connected, but if you program the DK with the blinky example first and perform an eraseall operation, the DK will stop blinking if the eraseall operation is performed on the DK instead of the external board. 
 You may also read out the FICR->INFO registers, to verify which chip is being programmed, given that the chip on the DK and external board is not the same variant/package/revision. 
 $ nrfjprog --memrd 0x10000100 --w 32 --n 20
0x10000100: 00052832 41414531 00002000 00000040 |2(..1EAA. ..@...|
0x10000110: 00000200 |....| 
 Best regards, Jørgen

nRF52 DK P20 debug out -- how do I know it is connected?

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