Sparkfun Pro Micro internal pullup question

[Youkai]

I have a couple questions about the Sparkfun Pro Micro and it's internal pullup resistors.

1) Which of the pins have this functionality? I looked at the data sheet and can't figure it out. If anyone could point me to the location of the reference for this so I know how to find it in the future I'd appreciate it.

2) If I have a pin set to pullup then I should be able to connect that pin directly to ground through a normally open switch and detect a button press by looking for a read of "0". Is that correct?

3) I saw something while I was trying to figure this out that said that pullup's are better than pulldown's though I didn't understand the guy's explanation as to why. Could someone elaborate please?

4) If I use internal pullups do I need to actually model it in the schematic or could I put a text node that says something like "all buttons use internal pullup"? I get that it's my schematic and I can do what I want but what's the norm?

[pcprogrammer]

1) I looked up the Sparkfun Pro Micro and it states to use the ATmega32U4 MCU. The datasheet found here can tell you all about which pin has the pull up feature you need.

2) When a pin is setup as input with a pull up, then yes a switch connected to ground will make it read zero when closed and one when opened, but with the internal pull up being between 20K and 50K ohm you can have more problems with bouncing of the keys. This can be handled in software or by using additional capacitors and resistors to filter it externally.

3) Point to the explanation given and I might be able to elaborate on it. In principle there is no difference between them.

4) There is no need to express this in your schematic. The schematic just shows the circuit as it is made. If the schematic is also used for the software development without further documentation, then it would be beneficial to place some text stating the need for using the internal pull ups of the MCU.

[bidrohini1]

I think you'd better post this to sparkfun forum. They can give more authentic info regarding their own product.