XIAO Internal Pull-up Resistors

Products & Technology XIAO
10

Short answer: The Xiao does NOT have/enable built in pull-up resistors.

Long answer: After noticing some odd behavior while shrinking circuit that works fine on an UNO, I did some digging, and then ended up searching online and finding this thread… The code compiles just fine with the INPUT_PULLUP specified, but does not actually do what is expected.

So I tested my 3 Xiao units bare (i.e only the USB connected) with the following sketch:

void setup() {
  Serial.begin(9600);
  for (int i = 0; i < 11; i++)
    pinMode(i, INPUT);
}
void loop() {
  for (int i = 0; i < 11; i++)
    Serial.printf("%c:%i ", (char)(i + 65), analogRead(i));
  Serial.println();
  delay(100);
}

Then again, but this time replaced pinMode(i, INPUT); with pinMode(i, INPUT_PULLUP);

Using the Arduino IDE ‘Serial Plotter’ I got the following charts:

pulluptest
pulluptest1202×1084 483 KB

Running a similar test on an Uno/Nano output consistent values at 1023 on all analog pins when INPUT_PULLUP was used (except A6 and A7 on the Nano, which dipped a bit, but still over 1000).

I guess I will be adding some external pullups to my Xiao circuits. :roll_eyes:

[Mac OS 10.14.6 / Arduino IDE 1.8.13 / Seeed SAMD Boards 1.8.1]