Pull up resistors in PIC Microcontrollers

[electronicsLearner77]

This is a general question and in particular to pic, internal to micro controllers there are pull up, pull down, weak pull up, weak pull down registers for enabling and disabling. I never touch this registers in general. How important these registers. Can someone please explain in case if i enable weak pull up or pull down. What actually happens inside the controller?

 

[Minder]

I generally do not use them, they are not really physical resistors, but equal to around 10K/15K equivalent, from Mosfets that can be turned on and off.
M.

 

[BobK]

They are used to avoid the need for an external resistor. For example, switch inputs require a pullup or pulldown so the state of the input is defined when the switch is open.

That said, I have just made a board using a weak pullup for a switch input, and I can trigger the switch by touching the contacts on the bottom of the board, so the pullup is really weak. In the next revision, I intend to use an external resistor.

Bob