Pull-up Resistor: A pull-up resistor connects the GPIO pin to the supply voltage (Vcc or +5V) through a resistor. This ensures that when the external signal is disconnected or high impedance, the pin is pulled to a logic high state. When the external signal connects to ground, it can ...
Tested it for all GPIOs that can be a DI. Works for all of them but not for GPIO34 ... GPIO39. They work as input but get not pulled up. Same with INPUT_PULLDOWN. These input-only pins don't have PU/PD circuits. OK, thanks for the information. ...