RE: If the nRESET is held low of nRF52840, would it shut it down?

kaushalyasat — Tue, 13 Jan 2026 23:07:46 GMT

Hi Samruddhi,

Thanks for the quick reply. I also couldn't find the state of SWD interface when chip is in reset state. If it is active, of course this method is not going to work. I will try muxing SWD lines.

Cheers,

Kaushalya

RE: If the nRESET is held low of nRF52840, would it shut it down?

Samruddhi Jadhav — Tue, 13 Jan 2026 14:47:50 GMT

Hello,

In general, holding nRESET low should keep the device in reset. This means the CPU doesn't run your programme and the GPIOs are not actively driven. As long as VDD is present, the device/chip is still powered. It is not completely powered off. During reset, the debug block can still be active and SWD can still be used. According to our documentation, there is no statement about if SWDIO is guaranteed to be high impedance or inactive while nRESET is held low for nRF52840. They do not mention the method which you are describing or that nRF52840 in reset will never drive SWDIO and disturb the bus so I cannot validate this approach.

Let me know if you have any further questions.

Best Regards,

Samruddhi