Dokument erweitert

tools/builtInChips/PC.hdl

@@ -1,17 +1,18 @@
 // This file is part of www.nand2tetris.org
 // and the book "The Elements of Computing Systems"
 // by Nisan and Schocken, MIT Press.
-// File name: tools/builtIn/PC.hdl
+// File name: tools/builtInChips/PC.hdl
 
 /**
- * 16-bit counter with load and reset controls.
+ * A 16-bit counter with increment, load, and reset modes.
+ * if      (inc(t) == 1)   out(t+1) = out(t) + 1
+ * else if (load(t) == 1)  out(t+1) = in(t)
+ * else if (reset(t) == 1) out(t+1) = 0
+ * else                    out(t+1) = out(t).
  *
- * If reset(t-1) then out(t) = 0
- *    else if load(t-1) then out(t) = in(t-1)
- *         else if inc(t-1) then out(t) = out(t-1) + 1 (integer addition)
- *              else out(t) = out(t-1)
+ * To select a mode, assert the relevant control bit,
+ * and de-assert the other two bits. 
  */
-
 CHIP PC {
 
     IN  in[16], load, inc, reset;