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How do I design a 2 input or 3 input NAND gates using a 4 input NAND gate (like 7420)

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suman28pandit

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I want to design a selectable input NAND gate using IC 7420 which should work as a 2- or 3-input NAND gate even when 2 or 3 inputs are applied
 

Hi,

...or tie unused inputs to an appropriate logic level with a suitable value resistor.
 
If I understand you right, you want to let some pins occasionally be unconnected?
Just pull-up these pins. In case they are unconnected, they will have high level and the gate will act as 2- 3- input NAND (or NOT gate if you use 1- input).
 
Hi,

A bit late, but still...

0 + 0 + 0 + 0 = 1
1 + 0 + 0 + 0 = 0
0 + 1 + 0 + 0 = 0
0 + 0 + 1 + 0 = 0
0 + 0 + 0 + 1 = 0
1 + 1 + 0 + 0 = 0
etc.

NAND is only all 0s make a 1, any 1s make a 0.
 

d123 said:
Hi,

A bit late, but still...

0 + 0 + 0 + 0 = 1
1 + 0 + 0 + 0 = 0
0 + 1 + 0 + 0 = 0
0 + 0 + 1 + 0 = 0
0 + 0 + 0 + 1 = 0
1 + 1 + 0 + 0 = 0
etc.

NAND is only all 0s make a 1, any 1s make a 0.
Click to expand...

That is NOR, not NAND ;-)
NOR is 0 if any of the inputs is 1.
NAND is 0 if all of the inputs are 1.
 

Altaero said:
That is NOR, not NAND ;-)
NOR is 0 if any of the inputs is 1.
NAND is 0 if all of the inputs are 1.
Click to expand...

Oh dear, you're right, just as well you pointed it out, thanks.
 

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