NOR Gate – Logic Gates Tutorial

A NOR gate is a logic gate the place the output goes HIGH (or “1”) provided that all its inputs are LOW (or “0”). The schematic image for a NOR gate is just like the OR gate, simply with a circle on the output to point that it’s an inverted model of OR.

NOR gate truth table

“NOR” stands for NOT-OR as a result of it’s the identical as an OR gate with a NOT gate on the output.

NOR gate equivalent from OR and NOT
NOR gate equal utilizing OR and NOT gates

The logic or Boolean expression for a NOR gate is overline{A+B} = Q which signifies that:

If A or B is true, then Q is fake

Reality Desk

NOR gates can have greater than two inputs. However regardless of what number of inputs it has, it’s going to solely give out a HIGH or logic “1” if all its inputs are LOW. As quickly as one of many inputs goes HIGH, the output goes LOW.

2-input NOR Gate Reality Desk

NOR gate symbol
Enter A Enter B Output Q
0 0 1
0 1 0
1 0 0
1 1 0

3-input NOR Gate Reality Desk

3-input NOR gate
Enter A Enter B Enter C Output Q
0 0 0 1
0 0 1 0
0 1 0 0
0 1 1 0
1 0 0 0
1 0 1 0
1 1 0 0
1 1 1 0

Construct a Transistor NOR Gate with RTL

You possibly can construct a NOR gate from transistors and resistors. This method is named resistor-transistor logic (RTL).

A NOR gate built with transistors and resistors logic (RTL)
NOR gate with transistors and resistors

If both A or B is excessive, one of many transistors activates. When one of many transistors is turned on, X is pulled low by means of the transistor.

It’s enjoyable to understand how you might construct it with transistors and resistors. But it surely’s probably not sensible to make use of that many parts simply to make a easy logic gate. Fortunately, there are a lot of ICs which have NOR gates that you should utilize out-of-the-box.

IC Options with NOR Gates

Pinout for the 4001 IC

If you wish to experiment and construct circuits with NOR gates, you’ll discover them in each the 4000 IC collection and the 7400 IC collection:

  • 4001: 4 2-input NOR gates
  • 4025: Three 3-input NOR gates
  • 4572: One NOR gate (plus a couple of different gates)
  • 74HC02: 4 2-input NOR gates (HC is the household, may also be LS/HCT/…)
  • 74HC27: Three 3-input NOR gates (HC is the household, may also be LS/HCT/…)

These ought to all be obtainable as hobbyist-friendly through-hole chips. Simply be sure to purchase the DIP bundle model.

NOR Instance Circuit: SR Latch

A typical circuit you may construct with two NOR gates is an SR latch. It is going to keep in mind the final output worth it had, so it’s a easy type of reminiscence.

Within the following circuit, you may flip the Mild-Emitting Diode (LED) on by urgent the On button. The LED will keep on even after you launch the button. To show the LED off, you may press the Off button.

Schematic for SR latch with buttons

The circuit makes use of two buttons (ON and OFF) to Set the output to HIGH or Reset the output to LOW. The 2 gates are set as much as create an SR latch that remembers the output for so long as the circuit has energy.

Subsequent Step within the Logic Gates Tutorial

Try the opposite articles on this logic gates tutorial:

NOT Gate/Inverter
AND Gate
OR Gate
NOR Gate – (You might be right here)
XOR Gate

Again to the Logic Gates Overview


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