What is the "R" pad on the bottom of the QT Py SAMD21 board

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mmryspace
 
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What is the "R" pad on the bottom of the QT Py SAMD21 board

Post by mmryspace »

Hi, I am just getting started with the QT Py SAMD21 and reading through the overview guide. In the pinout section it does not indicate what the "R" pad on the bottom of the board does. Is is related to the SWD debug pins or something else? My main concern is in doing any PCB design. The QT Py is described as Xiao compatible. However, the Xiao is slightly different on the bottom. I'd be using the Xiao footprint as a reference but they're not totally compatible due to the pad difference. Here's the bottom of the Xiao for reference: https://files.seeedstudio.com/wiki/Seee ... g/new1.png

Any clarification on the pin and/ or guidance is greatly appreciated.

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westfw
 
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Re: What is the "R" pad on the bottom of the QT Py SAMD21 board

Post by westfw »

"!RESET" signal.

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mmryspace
 
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Re: What is the "R" pad on the bottom of the QT Py SAMD21 board

Post by mmryspace »

westfw wrote: Thu Sep 15, 2022 6:46 pm "!RESET" signal.
Thanks so much for the reply. Can you please say more? For example: Does this relate to the SWD Debug pins? Does "!RESET" translate to "NOT RESET" ? Does this pad mirror the reset button on top of the board and / or is for a pogo pin or ? Thanks for any insights you can provide.

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westfw
 
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Re: What is the "R" pad on the bottom of the QT Py SAMD21 board

Post by westfw »

Does "!RESET" translate to "NOT RESET"? Does this pad mirror the reset button on top of the board
Yes. It connects directly to the "/Reset" pin on the microcontroller, which is also connected to the reset switch. It's "NOT" in the sense that it is "active-low" - connecting to ground causes a reset. Being pulled up to +3.3V (the default, via an internal pullup) lets the chip run.
Does this relate to the SWD Debug pins?
I'm not positive how RESET ties into SWD. Most SWD "programmers" have a pin that they want to connect to RESET, but it's also supposed to be possible to speak SWD to microcontrollers even while they are running. So it shouldn't be NECESSARY. I imagine it make the initial bootloader programming and test of the board much more straightforward, via a pogo-pin-sporting test fixture.

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mmryspace
 
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Re: What is the "R" pad on the bottom of the QT Py SAMD21 board

Post by mmryspace »

Many many thanks for these detailed responses! This is very helpful going forward. I really appreciate the help.

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