MKR Boards and Pins 11 and 12 always pulled up?

Hi,
I have been doing some intense programming on MKR ZERO and MKR WIFI 1010 boards and have come across a potential issue, or potential feature of pins 11 and 12 (SDA and SCL) on those boards.

These pins seem to be pulled up to 3.3v all the time, even if I configure them as

pinMode(11,INPUT);

With NO OTHER CODE, no libraries, nothing, especially not Wire!
The attached oscilloscope image shows pin 3 in blue and pin 11 in green, both configured as simple INPUT. As one can see, pin 11 is pulled up to 3.3v and pin 3 is floating around 0v.
My questions are:

  • Is this normal behavior ? I have not seen the equivalent on the ATMEL based boards, but maybe I just failed to observe properly?
  • Is there any way to disable the pull up, or at least get the value of the resistance used?
  • Should I inform arduino.cc or do they already know about this and/or did they do this intentionally?

Thanks for any thoughts,
Bob

There should be a schematic on the store's product page for those boards :wink:

You can find the schematics on the "Documentation" tab of the product page. The schematic for the MKR Zero:
https://store.arduino.cc/arduino-mkr-zero-i2s-bus-sd-for-sound-music-digital-audio-data
Shows 4.7K pull up resistors on these lines. Interestingly, they are marked "DNP" (do not place/populate), but they are populated on my board.

Clipboard01.png

Clipboard01.png

Indeed on mine also, they pull up; also on the MKR WIF 1010 as well as the MKR ZERO.

So these pins are sadly unusable in my application... sniff, oh well, at least this confirms that I am not crazy :wink:

Cheers!
Bob

On the MKR WiFi 1010 they are not marked “DNP”. The reason is that they are needed for the onboard ATECC508 crypto chip.

The MKR Zero actually has a footprint for the ATECC508, but it is “DNP” due to not being essential for a board without built-in networking connectivity. I think that’s the reason why the pull-up resistors were marked DNP on the MKR Zero. It shouldn’t be too difficult to remove those resistors on the MKR Zero. It’s surface mount, but there isn’t anything crowded too closely to the resistors.

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