You can use the register setting to select input and output status for the general-purpose port. At high impedance, the pin does not output both "H" and "L" because PMOS and NMOS are turned off. For pull-up, the pin has a pull-up resistor connected.
For N-channel open output, the pin outputs "L" or is in the high-impedance state because PMOS is turned off. For CMOS output, the pin outputs "H" or "L" because PMOS/NMOS is turned on/off.
