That master can use data to illustrate the role of pull up and pull down resistors

There are three different connections to the outside of the chip input pins: a connection with a pull-up resistor, a connection with a pull-down resistor, and a "floating" connection. In layman's terms, if a pin of a chip is connected to a power supply (VCC) through a resistor, that resistor is called a "pull-up resistor".

Correspondingly, if a pin of a chip is connected to ground (GND) through a resistor, the corresponding resistor is called a "pull-down resistor". In this practice, the dangling chip pins are initialized high or low by a pull-up or pull-down resistor. According to the actual situation, the value of the pull-up resistor and the pull-down resistor can be between 1k and 10k, and the resistance value is related to the quiescent current and system power consumption.

A look at the encyclopedia has a good explanation.

Only explain the improvement of the anti-electromagnetic interference ability of the bus, if there is no pull-up or pull-down resistance, the line impedance of the bus is higher, let's say 1 megaohm, when a tens of microamperes of interference signal enters the bus system, then the level generated can be as high as tens of volts, what do you say should be done at this time?

Assuming a pull-up or pull-down resistance of 5 thousand ohms, then even if there is an interference signal of 100 microamps entering the bus system, then the level generated will be voltile.

You'll understand what a pull-up or pull-down resistor does.

The pull-up resistor is to connect one pin of the resistor to the VCC, and the other pin to the chip pin that needs to be pulled up.

The pull-down resistor is to connect one pin of the resistor to GND, and the other pin to the chip pin that needs to be pulled down. The size is generally 1 10k, and it is mainly used in the pins of the mid-section, reset, chip selection, control and open-drain output. The function is to prevent instability caused by the system reset.

Pull-up is the embedding of an uncertain signal high through a resistor! The resistor also acts as a current limiter! The same goes for drop-downs!

The pull-up is the injection current into the device, and the pull-down is the output current. Weak and strong are only the resistance of the pull-up resistor, and there is no strict distinction. For non-collector (or drain) open output circuits (such as ordinary gate circuits) where the ability to increase current and voltage is limited, the function of the pull-up resistor is mainly to output the current channel for the open collector output circuit.

First, the role of the pull-up resistor:

On the CMOS chip, in order to prevent damage caused by static electricity, the unused pins cannot be suspended, and the pull-up resistor is generally connected to reduce the input impedance and provide a load release path. The pins of the chip are added with a pull resistor to increase the output level, thereby improving the noise tolerance of the input signal of the chip and enhancing the anti-interference ability. Improve the anti-electromagnetic interference ability of the bus, and it is easier to accept external electromagnetic interference when the pin is suspended.

Second, the role of the pull-down resistor:

Improve the noise tolerance of the chip input signal: If the input terminal is in a high-impedance state, or the high-impedance input terminal is in a suspended state, it is necessary to add pull or pull down at this time to avoid receiving random levels and affecting the circuit work.

Similarly, if the output is passive, it is necessary to add a pull or pull-down, e.g. the output is only a collector of a transistor. In this way, the noise tolerance of the chip input signal is improved and the anti-interference ability is enhanced.

3. Differences: 1. Different meanings;

Pull-up blot resistor: An uncertain signal is connected to the power supply VCC through a resistor and fixed at a high level;

Pull-down resistor: An uncertain signal is connected to ground GND through a resistor and fixed at a low level;

2. Different roles:

Pull-up is the injection of current into the device; current sink; When an IO port connected to a pull-up resistor is set to the input state, it is normally high;

Pull-down resistor: Pull-down is the output current from the device; source current; When an IO port connected to a pull-down resistor is set to the input state, it is normally low;

Principle

On the wire to which the pull-up resistor is connected, the pull-up resistor "weakly" pulls the input voltage signal "high" if the external component is not enabled. When the external components are not connected, the outside "looks" high impedance to the input. In this case, the voltage at the input port can be pulled high by a pull-up resistor.

If the external component is enabled, it will cancel the high level set by the wide stool set by the pull-up resistor. In this way, the pull-up resistor allows the pins to maintain a definite logic level even when no external components are connected.

The above content reference: Encyclopedia - Pull-up resistor.

Pull-up resistors and pull-down resistors are used to determine the normal high and low levels in digital circuits, without these resistors, the port may have a voltage between high and low levels, which is very unstable, so some ports have to be connected to high or low levels even if they are not used to ensure stable operation.

1. Pull-up resistance copy: will not attack.

The determined signal, connected to the power supply VCC by a resistor, is fixed at a high level.

Function: Pull-up is to inject current into the device; current sink; When an IO port connected to a pull-up resistor is set to the input state, it is normally high;

2. Pull-down resistor: An uncertain signal is connected to ground GND through a resistor and fixed at a low level.

Function: Pull-down is the output current from the device; source current; When an IO port connected to a pull-down resistor is set to the input state, it is normally low;

The common function of the pull-up resistor and the pull-down resistor is to avoid the "suspension" of the voltage and cause the instability of the circuit.

The pull-up resistor is the signal outside the IC, connected to the power through a resistor, the pull-down resistor is the letter inside the IC outside the capacitance, and the pull-up resistor is connected to GND through a resistor In most cases, the role of the pull-up resistor is to give the signal a voltage alignment, provided that there is no pull-up inside the IC.

The effect of the pull-down resistor is to make the initial state of the signal low in most cases

The so-called upper refers to the high level; By down, I mean low. Pull-up is to connect the signal to the power supply through a resistor, which is generally used for clock signals, data signals, etc. Pull-down, which is to connect the signal to ground through a resistor, is generally used to protect the signal.

This is designed according to the needs of the circuit, and the main purpose is to prevent interference and increase the stability of the circuit.

If there is no pull-up, the clock and data signals are prone to errors, after all, the CPU has limited power, and it is difficult to provide a high-level signal when there are many bus lines. Once these signals are pulled down to a certain voltage by load or interference, the CPU cannot receive information and send instructions correctly, and can only constantly reset and restart.

If there is no pull-down, the protection circuit is very susceptible to external interference, which makes the CPU mistakenly think that there is a problem with the protected object and takes protection actions, resulting in false protection.

Pull up and down, to be set according to the circuit requirements.

The pull-down resistors of pull-up resistors are actually shunt effects, but the positions used are different, so they are named pull-up and pull-down resistors.

However, whether it is a pull-up or pull-down resistor, its role is to limit the current, in fact, you don't need to pay attention to the up or down, just understand why he does it.

It may also be another name for the top bias resistor and the lower bias resistor, which is generally to make the transistor have a stable and reliable operating voltage.