As digital circuit works in low current, connecting the logic pins directly to the supply voltage or the ground is not a good choice. Now, if we replace the High and Low value with the actual voltage value then the High will be the logic level HIGH (lets say 5V) and Low will be the ground or 0v.Ī Pull-up resistor is used to make the default state of the digital pin as High or to the logic level (in the above image it is 5V) and a Pull-Down resistor does exactly opposite, it makes the default state of the digital pin as Low (0V).īut why we need those resistors instead we could connect the digital logic pins directly to the Logic level voltage or with the ground like the below image? So, in each case, the state gets changed as shown below. In both cases, we need to make the digital pin either ‘ High’ or ‘ Low’ but it cannot be left floating. In either case, we need to hold the digital pin either 0 and then change the state to 1 or we need to hold it 0 and then change to 1. In some cases, we need to change the state from 0 to 1 or from 1 to 0. If we consider a digital circuit, the pins are always be either 0 or 1. What are Pull-up and Pull-Down Resistor and Why we need them? Resistance is measured in Ohm with a sign of Ω. There are many different types of resistors. It is a passive component which provides resistance when current flow through it. Resistors are current limiting devices with are used abundantly in electronics circuits and products.
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