
XOR using NAND gates
Create an XOR gate using only NAND gates. (BTW, mostly all circuit problems assume you have two inputs plus 0 and 1 also as inputs).
* * *
Don't know if somebody has posted the answer yet, but it's not on the question page.
a XOR b
== (a AND NOT b) OR (b AND NOT a)
(Definition of XOR)
== (a NAND NOT b) NAND (b NAND NOT a)
(By De Morgan's Law)
== (a NAND (b NAND b)) NAND (b NAND (a NAND a))
(NOT x is equivalent to x NAND x)
I guess this is the simplest solution with 5 NAND gates.
S.C.
Friday, February 7, 2003
Here's my solution:
[((a NAND b) NAND a) NAND ((a NAND b) NAND b)]
As you can see, you can share the a NAND b. So, you only need 4 NAND gates. Sorry, but I don't have a derivation, but this can easily be proved using truth tables. This solution came naturally to me! I just wanted to convert the truth table for a NAND to the XOR and noticed that there is only one difference (0,0 case).
Adil
Monday, March 3, 2003
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