# What happens if pull-up resistor too high?

## What happens if pull-up resistor too high?

If the pull-up resistance value is too high, combined with a large leakage current of the input pin, the input voltage can become insufficient when the switch is open. This condition is called having a weak pull-up.

## What is the purpose of a pull-up resistor?

Pull-up resistors are fixed value resistors used between the connection of a voltage supply and a particular pin in a digital logic circuit. More commonly paired with switches, its purpose is to ensure the voltage between Ground and Vcc is actively controlled when the switch is open.

Should I use pull up or pull-down resistors?

Pull-up Resistor Summary A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.

How do you calculate pull-up resistors?

In order to calculate pull-up and pull-down resistance, we need to first apply the formula in Ohm’s Law: Resistance = Voltage/Current, or R= V/I.

### Why is pull-up resistor needed for an open collector gate?

A pull-up resistor is a resistor used to keep a given point in a circuit HIGH when in the active state. Why is a pull-up resistor needed when connecting TTL logic to CMOS logic? An open collector output can current, but it cannot . A universal logic gate is one, which can be used to generate any logic function.

### What is the difference between a pull-up and pull-down resistor?

A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.

Why does Port 0 needs pull-up resistors?

Port 0 of 8051 does not have internal pull up resistors like the remaining 3 ports. Hence we need to use external resistors. because it does not have an internal pull up. Port 0 can sink more current than other ports.

Does the value of a pull-up resistor matter?

The lower the resistance, the more power will be used when the button is hit. You generally want a large resistor value (10kΩ), but you don’t want it too large as to conflict with condition 2. A 4MΩ resistor might work as a pull-up, but its resistance is so large (or weak) that it may not do its job 100% of the time.

#### Which port required external pull-up resistor?

When we use external pull-ups it becomes general purpose port. Again, port 0 is open drain hence it requires pull-ups and all other ports are not having open drain its not left to user. If port 0 has to be used as i/o port its must to connect pull up resistor. Hope you clear with this answer.

#### How does a pull-up and pull-down resistor work?

Why does port 0 need pull-up resistors?

Port 0 of 8051 does not have internal pull up resistors like the remaining 3 ports. Hence we need to use external resistors.

How should a pull-up resistor and a button be wired?

One pull down resistor is connected to the first input of the AND gate. The pushbutton is connected to the positive voltage, and then, a pull-down resistor is connected to GND. If the push button is not pressed, AND gate input will be low. If the push button is pressed, AND gate input will be high.

## How do you calculate the pull-up resistor?

• August 21, 2022