7402 IC Quad 2-Input NOR Gate
7402 is a LOGIC GATE IC and a member of the 74XXYY IC series which are logic gates. There are four NOR gates in the IC and each gate has two inputs, hence the name QUADRUPLE TWO INPUT NOR GATE. The gates in the chip are designed by low-power SCHOTTKY TRANSISTORS.
7402 Pin configuration
7402 is a 14 PIN IC as shown in the pinout diagram. The chip is available in different packages and is chosen depending on requirement. The description for each pin is given below.
| Pin Number | Description |
| NORGATE 1 | |
| 2 | 1A-INPUT1 of GATE 1 |
| 3 | 1B-INPUT2 of GATE 1 |
| 1 | 1Y-OUTPUT of GATE1 |
| NORGATE 2 | |
| 5 | 2A-INPUT1 of GATE 2 |
| 6 | 2B-INPUT2 of GATE 2 |
| 4 | 2Y-OUTPUT of GATE2 |
| NORGATE 3 | |
| 8 | 3A-INPUT1 of GATE 3 |
| 9 | 3B-INPUT2 of GATE 3 |
| 10 | 3Y-OUTPUT of GATE3 |
| NORGATE 4 | |
| 11 | 4A-INPUT1 of GATE 4 |
| 12 | 4B-INPUT2 of GATE 4 |
| 13 | 4Y-OUTPUT of GATE4 |
| SHARED TERMINALS | |
| 7 | GND- Connected to ground |
| 14 | VCC-Connected to positive voltage to provide power to all four gates |
Specifications
| Product Attribute | Attribute Value |
| Product Category: | Logic Gates |
| Logic Function: | NOR |
| Number of Gates: | 4 Gate |
| Number of Input Lines: | 8 Input |
| Package/Case: | PDIP-14 |
| Number of Output Lines: | 4 Output |
| Low Level Output Current: | 5.2 mA |
| High Level Output Current: | – 5.2 mA |
| Propagation Delay Time: | 8 ns |
| Supply Voltage – Min: | 2 V |
| Supply Voltage – Max: | 6 V |
| Minimum Operating Temperature: | – 40 C |
| Maximum Operating Temperature: | + 85 C |
| Mounting Style: | Through Hole |
| Function: | Quad 2-Input |
| Logic Type: | 2-Input NOR |
| Number of Bits: | 4 bit |
| Operating Supply Current: | 20 uA |
| Operating Supply Voltage: | 5 V |
| Operating Temperature Range: | – 40 C to + 85 C |
| Output Type: | CMOS |
| Product: | Single-Function Gates |
| Product Type: | Logic Gates |
Where to use 7402 IC
There are many reasons for using 7402. Here are a few cases of why it is used.
- The chip is basically used when the (NOR) logic function is required. The chip has four (NOR) gates in it. We can use one or all gates.
- When you want a logic inverter. NOR gates in this chip can be reconnected to make them NOT gates. Each NOR gate can form a single NOT gate. So we can make the 7402 chip a four NOT gate chip if necessary.
- Where high-speed NOR operation is necessary. As mentioned earlier the gates in the chip are designed by SCHOTTKY TRANSISTORS. With them, the switching delays of gates are minimized. Because of this, the chip can be used high speed applications.
- 7402 is one of the cheapest IC. It is really popular and is available everywhere.
- The chip also provides TTL outputs which are a must in some systems.
How to use 7402
Like every other chip in the 7400 series, this IC needs to be connected to power before you can use it. Most 7400 ICs support a VCC voltage of 5V. One difference between the HC and LS version of the chip is that the 74HC02 supports 2V to 6V, while the 74LS02 supports only 5V.
Once it’s connected, you can use any of the four basic NOR gates inside.
Each NOR gate here performs NOR operation for two logic inputs. Also, the NOR gate is a combination of OR gate and NOT gate.
So NOR = OR + NOT.
The truth table of the NOR gate is given as,
| Input1 | Input2 | OR Output | NOR Output |
| LOW | LOW | LOW | HIGH |
| HIGH | LOW | HIGH | LOW |
| LOW | HIGH | HIGH | LOW |
| HIGH | HIGH | HIGH | LOW |
For realizing the above truth table let us take a simplified NOR gate and have it connected as shown below.
In the circuit, two transistors are connected to form a NOR gate. The two inputs are driven out from the bases of two transistors. These two inputs are connected to buttons. The output of the gate is taken out from the joint collector of both transistors. This output is connected to an LED through a current-limiting resistor. This LED is connected to detect the state of the output. The buttons are connected to change the logic of inputs.
Now let us consider a few states:
1. When both buttons are not pressed. In that state, the current flow through the base of both transistors will be zero. Because the base current is zero transistors Q1 and Q2 will be OFF. So the total supply voltage VCC appears across the transistors Q1 and also across Q2. Because output Y1 is nothing but voltage across transistors Q1 or Q2 it will be HIGH. So when INPUTS = LOW, OUTPUT = HIGH.
2. When one of the buttons is pressed. Only the relative transistor will be ON leaving the other OFF. The ON transistor will act as a short circuit and it will overlap the OFF transistor. With that, the total drop across both transistors will be zero. Because the transistor drop is zero Y1 will be LOW. So when one INPUT = HIGH, OUTPUT = LOW.
3. When both buttons are pressed. Both transistors will be ON and the voltage across both of them will be zero. Because the transistor drop is zero Y1 will be LOW. So when both INPUTs = HIGH, OUTPUT = LOW.
After verifying the three states, you can tell that we have satisfied the above truth table. The output equation for NOR gate can be given as, Y=A+B.
Like this, we can use each gate of the chip depending on the requirement.
Applications
- General purpose NOR logic operation
- Digital Electronics
- Servers
- ALUs
- Memory units
- Networking
- Digital systems
