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What logic gates are required for Turing completeness?

Asked 2011-02-05T18:54:07.807
39

My son has been playing Little Big Planet 2 lately, and I noticed that the game editor allows AND gates, OR gates and NOT gates... Is it Turing complete? If so, can anyone recommend a source for learning to turn those primitives into something like a higher level conditional if?

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You need NOT and one of AND or OR to be able to do all binary logic. This is DeMorgan's Law, basically.

However, this is not sufficient for Turing completeness. For that you also need random (or reducably equivalent) access (theoretically) infinite memory.

Odds are, you'll be able to build a flip flop (a D flip flop is built using NANDs, so it's straightforward) using the available logic gates. From those, you can build a register, and with enough of those you'll be equipped to build some simple programs.

answered 2011-02-05T20:19:09.840
4

An idea: you should be able to construct a NAND gate, so you can then build a XOR gate. With XOR and AND you can build a half-adder. Combine half-adders to build a full-adder. That would be a start at least.

NAND and NOR are basic building blocks for other gates so chances are Turing completeness is just around the corner.

answered 2011-02-05T19:05:38.120

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