Re: Full adder

Posted by cadet1620 on Feb 06, 2013; 6:29pm
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/Full-adder-tp4026235p4026245.html

Getting to the 9 Nand solution comes with experience. The 4 Nands in a diamond pattern are the known best Nand implementation of Xor, which is the adding part of a half-adder. Conveniently, the first Nand in each Xor generates ~carry. The two ~carrys can be Ored together with a Nand because of DeMorgan's law.

If you take a look at Why We Like Abstraction there's an ALU done entirely with Nands. You'll see a lot of these 9-Nand adders.

--Mark