pull pull down meaningon GPIO

[yefj]

Hello, In the photo bellow there is a diagram for general purpose input output(GPIO).
When they say in the manual "The following code configures pin 5 from Port C as a digital input with pull-up and filter"
We see in the diagram is just connecting the output to VDD and pull down is connecting the output to GND.
So if we have digital input of a square wave then the pull up cancels it totally because we have path to VDD (OR) ground.
We ruin our signal by doing pullup or pull down.
What is it good for?
Thanks

 

[KlausST]

Hi,

Explain "ruin". Best if you can calculate volts.

Klaus

 

[betwixt]

You are not noticing the resistor symbols on the diagram.

The pull-up and pull-down are not direct connections to VDD or VSS, they enable a weak current source to maintain the pin in a known state when not being driven or having current drawn from it. The source is usually only a few uA so your external signal should easily drive against it. If in doubt, turn it off.

Brian.