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

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

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.

## What is a pull-up resistor used for?

Pull-up resistors are resistors used in logic circuits to ensure a well-defined logical level at a pin under all conditions. As a reminder, digital logic circuits have three logic states: high, low and floating (or high impedance).

What is pull up or pull down for an input or output?

Pull-up and pull-down are methods of processing digital signal lines by connecting them to the power supply side and ground side, respectively. Signals may be connected directly or via a resistor. (1) Direct connection. Direct connection means fixing the input level of the dedicated input pin to either high or low.

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### What is pull up transistor?

Suppose input is low, as a result the upper PMOS is ON but lower NMOS is OFF. Hence the output voltage is same as source voltage. That is why the PMOS here is called a “pull-up” transistor, as simply put one can say, “Output has been pulled up to source voltage” via the PMOS.

### Do transistors need pull down resistors?

Since an NPN transistor’s base is not a high impedance point like a MOSFET or a JFET, and the HFE of the transistor is less than 500, and at least 0.6V is needed to turn the transistor ON, a pull-down resistor is not critical, and in most cases is not even needed.

Why do we need pull up and pull down resistors?

To control the current flow, we need those pull-down or pull up resistors. A pull-up resistor allow controlled current flow from supply voltage source to the digital input pins, where the pull-down resistors could effectively control current flow from digital pins to the ground.

#### What is pull down resistor in microcontroller?

What is Pull-down Resistors. Similarly to pull-up resistors, pull-down resistors ensure the voltage between VCC and a microcontroller pin is actively controlled when the switch is open. However, instead of pulling a pin to a high value, such resistors pull the pin to a low valued instead.

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#### Why nMOS transistor is selected as pull down transistor?

Here pull up is nMOS transistor and pull down is pMOS transistor. When logic 1 is applied as input, nMOS transistor turns ON and PMOS transistor turns OFF. Hence, the output should get charged to Vdd. But due to threshold voltage effect, nMOS is not capable of passing Vdd/ good logical 1 at the output.

Why nMOS is pull down?

## What is a pull down network made of?

electronics Projects

Sr. No. Pull Up Network
(1) Pull up Network is used to make output as logic High
(2) Pull up network is made up of PMOS Transistors because of property of passing strong ‘1’
(3) As the mobility of PMOS transistor is lower than NMOS transistor, W/L ratio of PUN transistors is higher

## Which port needs pull up resistors?

An external pull-up resistor is needed when Port 0 is defined as an output port. Port 0 of the 8051 has two main functions: To be used as a simple input-output port and to access external memory in conjunction with Port 2.

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Why we use pull up and pull-down resistor?

### How to connect a pull up resistor?

Pull-up resistors are connected to the NAND gate inputs. A pull up resistor is connected to the first input of the NAND gate and positive voltage. A push button is connected to GND. When the push button is not pressed, the NAND gate input is high.

### What are pull up and pull down resistors?

Pull-up resistor definition. Pull-up resistors are resistors which are used to ensure that a wire is pulled to a high logical level in the absence of an input signal.

What is a pull up and pull down resistor?

A pull up or pull down resistor “pulls” the voltage of an output terminal to the positive or negative rail voltage. It is typically used when a transistor drives an output and when the transistor is off, the output terminal is effectively disconnected from everything.

#### What is pull up and pull down resistor in microcontroller?

For any microcontroller in an embedded system such as Arduino, pull-up and pull-down resistors utilize input and output signals for communication with external hardware devices, the General Purpose Input Output (GPIO). Implementing the pull-up and pull-down resistors in the circuit will let you achieve either ‘high’ or ‘low’ states.