Hello everyone,
We’re developing a prototype using the nRF52840 MCU, and we need to flash a bootloader over SWD using a 1.8 V system powered by a PMIC. I’m exploring whether the nRF52840 DK can act as a programmer in this setup, or if we should use a dedicated J-Link. It is my understanding that the nRF52840 has no default bootloader uploaded on delivery, and hence, we will need to flash that ourselves. Currently the company i work for, does not have a SWD. Therefore, we will need to aquire one. A freind has recommended, the J-Link Base Compact. I looked it up on the devzone, and it seems people have had problems with this in the past:
Program issue with Segger JLink Base Compact
I have also looked at the nRF52840 DK. It is my understanding that there is an inbuilt J-Link IC, for SWD purposes. But, there is a problem.
At the moment, we use a Power management integrated circuit (PMIC). The PMIC outputs 1.8 V by default, and that is what we use to power the system. It is my understanding that the J-Link Base Compact has a target-voltage sense capabilities, so that we dont need a logic level shifter. It is also my understanding that the DK has a VTG pin for that purpose aswell. One question i have for the blog, is, "Can we use the VTG pin, so that the default 3.3 V of the DK, gets shifted to 1.8, so that the DK and the external device can communicate thorugh SWD?". If that is the case, can i just make the connections from connector P19:
(Ext is the external device, DK is the nRF52840 DK P19 connector)
nRF52840 DK (P19) → External Device
----------------------------------------
SWDIO → SWDIO
SWCLK → SWCLK
VTG → 1.8 V (from PMIC, pulled up with a resistor)
GND → GND
EXT_GND_DETECT → GND ?
RESET → RESET
Note: Unsure if EXT_GND_DETECT should be tied to ground or left floating — any guidance would be appreciated.
Would this work, or do i need the voltage level shifter?
Also, should the external device be powered by the DK, or should they have their own power?
Finally, does anyone have a recommendation? which board/SWD device would they use in this case?
Questions summerized:
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Can the nRF52840 DK’s VTG pin be used to match the DK’s SWD interface to a 1.8 V target?
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Would the following connections work safely?
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Is a voltage level shifter still required in this setup?
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Should the external target be powered by the DK, or from its own supply?
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Would you recommend another debug probe (e.g., J-Link Base Compact vs DK vs other options)?
Thank you for your attention to this matter everyone :), looking forward to your replies.
Best regards,
Philip V-L
