Which pin on the UNO is an input only.

Some time ago I was trying to get the out puts to blink an LED, there was one pin that would not work as it was an input only. I cant remember which pin it was. I woul appreciate the assistance and where I can get a description in pin brightness

All of the Uno pins can be set as INPUT or OUTPUT with the command pinMode(pin, INPUT); or pinMode(pin, OUTPUT);

There is also pinMode(pin, INPUT_PULLUP); which enables the internal pullup resistor to make the pin read as HIGH unless an external device (such as a switch) pulls it to GND.

...R

See the ATmega328P data sheet, section I/O Ports: Overview. It states that all port pins can be used for input and output. I'm not aware of exceptions from that rule.

In practice some pins are used for special functionality, like Reset and clock oscillator. More pins can be used by libraries, e.g. Serial RX and TX. Some pins (marked ~) can be used as PWM outputs for fine control of LED brightness, using analogWrite(), else a connected LED can only be turned on or off, using digitalWrite().

DrDiettrich:
See the ATmega328P data sheet, section I/O Ports: Overview. It states that all port pins can be used for input and output. I'm not aware of exceptions from that rule.

In practice some pins are used for special functionality, like Reset and clock oscillator. More pins can be used by libraries, e.g. Serial RX and TX. Some pins (marked ~) can be used as PWM outputs for fine control of LED brightness, using analogWrite(), else a connected LED can only be turned on or off, using digitalWrite().

Thank you!!

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