Program counter

sequentialChips/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/3/a/PC.hdl
+/**
+ * A 16-bit counter.
+ * if      reset(t): out(t+1) = 0
+ * else if load(t):  out(t+1) = in(t)
+ * else if inc(t):   out(t+1) = out(t) + 1
+ * else              out(t+1) = out(t)
+ */
+CHIP PC {
+    IN in[16], inc, load, reset;
+    OUT out[16];
+
+    PARTS:
+    Inc16(in=regout, out=increg);
+    Mux16(a=regout, b=increg, sel=inc, out=ri);
+    Mux16(a=ri, b=in, sel=load, out=ril);
+    Mux16(a=ril, b=false, sel=reset, out=regin);
+    Register(in=regin, load=true, out=regout, out=out);
+}
+