After reset pin 13 seems to be configured as an output

Official Hardware Classic UNO R4 Minima
1

On the Uno R4 Minima and Uno R4 WiFi, pin 13 seems to be made an output after reset, so if you do:

void setup() {
  Serial.begin(9600);
  delay(5000);
}

void loop () {
  Serial.println(digitalRead(13));
  delay(1000);
}

and apply 5V to the pin (via a resistor for safety), you still get 0.

As far as I understand it the usual Arduino convention is that all digital pins are inputs after reset, and to make a pin an output you have to call pinMode(13, OUTPUT), for example.

The way it is currently working is undesirable, because you might have pin 13 connected to a voltage input; an accidental reset could then cause excessive dissipation in the output driver.

2

Pin 13 is BUILTIN_LED and as such is defaulted to an output and seldom used as an input.

3

Pin 13 is BUILTIN_LED and as such is defaulted to an output

As far as I know no other Arduino board does this.

4

But Uno R4 does:

5

But Uno R4 does:

Which is why I'm reporting it as an error.

6

It isn't error but intentional as it is just a resistor and LED connected to pin instead of through a MOSFET or comparator.

7

Perhaps 'error' was the wrong word, but it's inconsistent with the Arduino Uno ATmega328P, and most other Arduino boards I'm aware of.

8

I've just tested the latest core, 1.0.2, and the problem is still there.

9

Have you brought it up as an issue on their github?

10

Good suggestion - thanks. Posted here:

After reset pin 13 is configured as an output

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