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diff --git a/projects/03/a/PC.hdl b/projects/03/a/PC.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/03/a/PC.hdl
+
+/**
+ * A 16-bit counter with load and reset control bits.
+ * if      (reset[t] == 1) out[t+1] = 0
+ * else if (load[t] == 1)  out[t+1] = in[t]
+ * else if (inc[t] == 1)   out[t+1] = out[t] + 1  (integer addition)
+ * else                    out[t+1] = out[t]
+ */
+
+CHIP PC {
+    IN in[16],load,inc,reset;
+    OUT out[16];
+
+    PARTS:
+	Register(in=fb, load=true, out=reg, out=out);
+	Inc16(in=reg, out=reg1);
+	Mux16(a=reg, b=reg1, sel=inc, out=cnt);
+	Mux16(a=cnt, b=in, sel=load, out=cntin);
+	Mux16(a=cntin, b=false, sel=reset, out=fb);
+}