Why does the resistor need to be pulled? The function of up and down resistors!

What is pull-up resistance? Both pull-up resistor and pull-down resistor are resistive components. The so-called pull-up resistor is connected to the positive pole of the power supply, while the pull-down resistor is connected to the negative pole or ground. Pulling up is the process of clamping an uncertain signal at a high level through a resistor, which simultaneously serves as a current limiting function. Pulling down is the same as clamping uncertain signals at a low level through a resistor.

So, what are the uses and differences between pull-up resistors and pull-down resistors?

1、 What are pull-up resistance and pull-down resistance

Pulling up is the process of clamping an uncertain signal at a high level through a resistor, which simultaneously serves as a current limiting function. The pull-down resistor is directly connected to the ground, and when a diode is connected, the end of the resistor is at a low level, clamping uncertain signals at a low level through a resistor. Pull up represents the input current of the device, and pull down represents the output current; The strength is only a difference in the resistance value of the pull-up resistor, without any strict distinction; For non collector (or drain) open circuit output circuits (such as ordinary gate circuits), the ability to provide current and voltage is limited, and the function of pull-up resistors is mainly to output current channels for collector open circuit output circuits.

2、 The role of pull-up resistance and pull-down resistance

The combined effect of pull-up resistance and pull-down resistance is to avoid voltage floating, which can cause instability in the circuit.

Pull-up resistance:

1. Concept: Connect an uncertain signal to the power supply VCC through a resistor and fix it at a high level;

2. Pulling up is injecting current into the device and injecting current;

3. When an IO port with an pull-up resistor is set to the input state, its normal state is high.

Pull down resistance:

1. Concept: Connect an uncertain signal to ground GND through a resistor and fix it at a low level;

2. Pull down is the output current from the device, pulling the current;

3. When an IO port with a pull-down resistor is set to the input state, its normal state is low.

Pull up is the injection of current into the device, pull down is the output current, weak or strong is only the difference in the resistance value of the pull-up resistor, and there is no strict distinction. For non collector (or drain) open circuit output circuits (such as ordinary gate circuits), the ability to increase current and voltage is limited. The main function of pull-up resistors is to output current channels for collector open circuit output circuits.

From this, it can be seen that the resistance from the power supply to the device pin is called the pull-up resistance, which is used to set the pin to a high level during normal use; The resistance from ground (GND) to the device pin is called a pull-down resistor, which is used to make the pin low during normal operation.