Internal Weak Pull-ups
Internal weak pull-up resistors enabled for each I/O pad using the WPUx register.
The pull-up is disabled automatically when either TRIS is set to an output or the pin is set as an analog input. These changes to TRIS and ANSEL will override WPU settings.
Enabling Pull-ups
The internal pull-up for a digital input pin is enabled by writing a '1' to the appropriate WPUx register. Writing a '0' to the WPUx register disables the pull-up.