Pullup Resistor Mode

Other Hardware General Electronics
1

I found this quote about pullup resistors in a thread about resistors making sure circuit with buttons read 0v at all times the switch is open. Does this mean I don't need to attach resistors in the mode at all because it's taken care of on the arduino?

liamorourke:
you might already know this but the input pins already have built in pull-up resistors which can be activated by adding the word PULLUP into your pinMode statement. Like this: -

pinMode("pin", INPUT_PULLUP);

as opposed to just: -

pinMode("pin", INPUT);

It just saves you the time taken to solder in a resistor and the little amount of money you would be spending on it.

2

If the switch is open, a pullup will ensure the pin reads HIGH.

3

Does this mean I don't need to attach resistors in the mode at all because it's taken care of on the arduino?

Yes, the internal pullup replaces an external resistor.

making sure circuit with buttons read 0v at all times the switch is open.

No, as per AWOLs comment, the pin is pulled HIGH (5V) with the pullup resistor (the name is a big hint). This means that when the switch is closed it will read LOW.