I'm trying to do an exercise, and it says to build a xnor gate using only 4 xor gate, and i'm having quite alot of trouble. Can someome give me a hand!
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What have you got so far? – beaker Oct 18 '15 at 23:11
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I doesnt know how to make the first 0 and 0 bit result to 1 – Breno Lopes Oct 18 '15 at 23:19
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If you're not allowed constants then it is not possible. There is no way to generate a 1 using only 0 and XOR gates. You can make a 0 constant by XORing any value with itself.
If you are allowed constants then it is trivial (and in fact only needs two XOR gates), since an XOR gate fed 1 in one input will become a NOT gate.
You basically always need some way to make an inverter (i.e. NOT gate) to do gate conversion in general.
Are you certain the question isn't reversed? Make an XOR gate using 4 XNOR gates?
ETA: Actually even reversing the question doesn't help without constants because there is no way to make a 0 using only 1 and XNOR gates. 1 can be produced by XNORing any value with itself.
Parakleta
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thats right! i think the person who's made this exercise is crazy! – Breno Lopes Oct 19 '15 at 13:44