Why are Due digital pins automatically pulling up?

Official Hardware Mega Due
1

I was testing the digital pins on the Due by the digitalRead() function and realized that unless i pull the pin low by connecting it to ground it is considered HIGH. I analogRead() the digital pins and they are showing ~217 out of 1023. My test code is shown below.

#define HREFpin 38

void setup() {
  pinMode(HREFpin,INPUT);
  Serial.begin(115200);
}

void loop() {
  Serial.println(digitalRead(HREFpin));
}

I am concerned that this will affect the my readings of the digital pins causing some readings to be HIGH when they aught to be LOW. Should i pull the pins down or leave them?

2

:wink:

Digital and analog pins , if left unconnected, will always "float" high. That is what you are seeing when you read an open pin!

David G.

3

But is it not a big inconvinience that the pins default to high?
If I use pinMode(pin, OUTPUT); I also have to use digitalWrite(pin, LOW);
And when programming all pins turns to High level outputs, and if the programming is interrupted or fails the pins remain in high state.
I might be wrong but it feels better if the outputs would default to LOW.

4

Pullups are standard so inputs can come from push buttons to ground and other
voltage devices with open-drain outputs.

The Due enables internal pullups by default because not all pins have hysteresis
built-in like the AVR ATmega series.