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Pi Pico W datasheet states:

3V3_EN connects to the on-board SMPS enable pin, and is pulled high (to VSYS) via a 100kΩ resistor. To disable the 3.3V (which also de-powers the RP2040), short this pin low.

and

RUN is the RP2040 enable pin, and has an internal (on-chip) pull-up resistor to 3.3V of about ~50kΩ. To reset RP2040, short this pin low.

Which means that RUN resets the microcontroller and 3V3_EN powers it off. Practically (in application) both sound to me as they will only reset the microcontroller. I tried also using both pins and haven't noticed any difference in the behavior: microcontroller starts over, once the pin is released (i.e. pulled up again).

So, the question is, what is the practical difference between using RUN pin or 3V3_EN in applications?

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  • 1
    (3) So, if you like, 3V3_EN is hardware power off/on reset, RUN is software reset.
    – tlfong01
    Sep 22, 2022 at 8:16
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    What will be the practical difference between software and hardware reset for Pi Pico then?
    – Vadim
    Sep 22, 2022 at 8:24
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    MicroPython Reset Functions docs.micropython.org/en/latest/library/machine.html (1) machine.reset() Resets the device in a manner similar to pushing the external RESET button. (2) machine.soft_reset() Performs a soft reset of the interpreter, deleting all Python objects and resetting the Python heap. (3) machine.reset_cause() Get the reset cause. See constants for the possible return values. (4) machine.bootloader([value]) Reset the device and enter its bootloader, typically used to put the device into a state where it can be programmed with new firmware.
    – tlfong01
    Sep 23, 2022 at 3:42
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    Rpi PicoW 3V3 En Schematic: imgur.com/a/gBluUTJ
    – tlfong01
    Sep 23, 2022 at 7:40
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    @tlfong01, great collection of the insights. It start crystalizing slowly so I can think of at least one practical consequence. With 3v3_en one powers off whole 3.3 V line, meaning that one would also reset any sensors or other components outside Pico board powered from it.
    – Vadim
    Sep 23, 2022 at 14:13

1 Answer 1

Reset to default
3

One difference is that you can detect whether the last reset occurred due to the power supply (eg. 3V3_EN), the RUN pin, or via the Rescue Debug Port, by checking the CHIP_RESET register.

See section 2.12.7. Source of Last Reset in the RP2040 Datasheet.

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