An adder/ subtractor in hardware

Activity 19 E:

A subtractor. I found a schematic for a subtractor. I am attempting to implement it and then create a test script and compare file for the hardware simulator. Using a 16 bit adder and two other 16 bit logic gates I think I have a hardware subtractor. I have tried two approaches neither  one works. The issue was my full adder had to a few changes now it seems to work great. And since it’s not a project in the book I don’t see an issue of posting the code.

//Created By Jeremy King for the hack computer

//The method of creating it came from

//http://www.play-hookey.com/digital/binary_subtraction.html

/**

 * 16-bit adder/subtractor: a + b = out   if sub == 0

 *                          a - b = out   if sub == 1

 */

CHIP Subtract16 {

    IN a[16], b[16], sub;

    OUT out[16];

    PARTS:

       //does not work

       //Accordding to articals I read it should work

    /*Not16(in=b,out=NotB);

       Inc16(in=NotB,out=outA);

       Mux16(a=b,b=outA,sel=sub,out=outc);

    revAdd16(a=a,outc=outc,sub=sub,out=out); */

      

       //works great

       //This is what creats the subtraction

       XOr16(a=sub,b=b,out=bout);

       //This adder has a third single bit input to start the carry

    revAdd16(a=a,outc=bout,sub=sub,out=out);

}