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Pin connections	Basic operation
Truth table	LINKS . . .

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Pin connections

The 4002 contains two 4-input NOR gates.

NC = no connection

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Truth table

The truth table of a 4-input NOR gate is:

In the table, '0' represents a LOW voltage, and '1' represents a HIGH voltage.

You can work out the correct number of lines in the truth table from 2 ⁿ , where n is the number of inputs. Here, n = 4, so there are 2 ⁴ = 16 lines. As you can see, the output of the gate is '1' only when all four inputs are '0'.

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Basic operation

You can investigate the behaviour of one of the 4-input NOR gates using this circuit:

The inputs of the gate must be connected, either to LOW or to HIGH, and must not be left open circuit. This is the function of the input switches with their pull-down resistors. To avoid loading the output of the gate, a transistor switch indicator circuit should be used. It is good practice with CMOS circuits to insert a decoupling capacitor, 47 µF or 100 µF, across the power supply. (This helps to prevent the transfer of spikes along the power supply rails.)

Don't forget - - Connect pin 14 of the 4002 to +9 V and pin 7 to 0 V.

This is the test circuit built on prototype board:

4002

In the prototype circuit, it is not essential to make connections to the unused gate. However, in any final circuit, all unused CMOS inputs must be connected either to HIGH or to LOW. Make it an absolute rule that CMOS inputs are never left open circuit.

There is no problem with CMOS outputs. Worry about the inputs and leave any unused outputs unconnected.

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Links

Cross references in the Beastie Zone: 4000, 3-input NOR + inverter, 4001 2-input NOR, 4025 3-input NOR, 4078 8-input NOR

Cross references in Design Electronics:

External links:

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