ATMega pullups enabled in Arduino?

Projects Programming
1

I was reading the datasheet on the ATMega328 and(as with PIC) i've noticed it has internal pull-ups in all ports individually selectable and so i was wondering:
¿When enabling a pin as digitalinput, does the pullup get automatically enabled?, if not, can i use the AVR-GCC config directives to enable them or will those break the Arduino port functions?

reference manual does not indicate anything about the pullups and i see that all the examples use external pullups/pulldowns

2

Thanks a lot Richard, i should've RTFM in more detail, can't believe i missed that :blush: ...

so yeah, that answers my quesiton, now i know how to set the internal pullups, case closed

3

Would you mind sharing this with the rest of the world?
Thanks,

4

Pullups are not enabled automatically.

To turn one on:
pinMode ( pinX, INPUT);
digitalWrite (pinX, HIGH);

5

nitromuse:
Would you mind sharing this with the rest of the world?
Thanks,

Nitro,
there was a reply from a user that's now been deleted -who knows why- that had the answer, anyway, here it is:

If you do a digitalwrite HIGH on a pin configured as input, it enabled the 20K internal weak pull-up
check: digitalWrite() - Arduino Reference
" If the pin is configured as an INPUT, writing a HIGH value with digitalWrite() will enable an internal 20K pullup resistor "

and from http://arduino.cc/en/Tutorial/DigitalPins

pinMode(pin, INPUT);           // set pin to input
digitalWrite(pin, HIGH);       // turn on pullup resistors