Projects, 01-06 completed

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diff --git a/projects/demo/Xor.hdl b/projects/demo/Xor.hdl
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+// This file is part of www.nand2tetris.org

+// and the book "The Elements of Computing Systems"

+// by Nisan and Schocken, MIT Press.

+// File name: projects/demo/Xor.hdl

+

+/**

+ *  Exclusive-or gate: true if either a is true and b is false, or

+ *  a is false and b is true; false otherwise.

+ *  QUESTION: how can the simulator execute this program properly without

+ *  HDL implementations of the underlying Not, And, and Or chip-parts?

+ *  Answer: since the demo folder contains no Not.hdl, And.hdl and Or.hdl

+ *  files, the simulator reverts to using their built-in implementations.

+ */

+

+CHIP Xor {

+    IN a, b;

+    OUT out;

+

+    PARTS:

+    Not (in=a, out=nota);

+    Not (in=b, out=notb);

+    And (a=a, b=notb, out=x);

+    And (a=nota, b=b, out=y);

+    Or (a=x, b=y, out=out);

+}
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