Pull Up and Pull Down Resistors
In this article, EPCB will give an explanation of pull up and pull down resistors which can help us to define the pins of chips.
There are three states about pins of chips. They can be LOW, which means voltage near 0V is fed into the pin. Pins can be HIGH, which means a voltage above half of the voltage fed into the chip's power supply is fed into the pin. Or pins can be floating, which means pins may go randomly either LOW or HIGH.
Pins float may because they have no clear defined voltage signal going into it. To make sure exactly what state it is, we use pull up and pull down resistors. Pull up resistors give a pin of a chip a clear HIGH signal. Pull down resistors give a pin of a chip a clear LOW signal. If you connect a resistor to a switch such as pushbuttons, both pull up and pull down resistors can switch states so that a pull up resistor can be bring a pin to a LOW state and a pull down resistor can bring a pin to a HIGH state.
The resistor value used for pull up and pull down resistors is usually 10KΩ or higher. Typical values are 10KΩ or 100KΩ.