>  Hi, 
>   
>  =20 
>   
>  For the fall '03 midterm 1, I was looking at question 10 b) and got a = 
>  little 
>  confused.  10 b) is referring to the program described above right?  So = 
>  why 
>  would it output ACDC (as in the solutions guide) as opposed to just 0001 
>  since XOR outputs only 0's and 1's? =20 
>   
>  =20 
>   
>  Thanks, 
>   
>  Michael =20 

(1) 10b is referring to the program above.

(2) The instruction 9CFF writes the register contents to the screen in
    hex, not in binary.

(3) I think you're still not understanding clearly the concepts of hex
    and xor.

    (a) Hex is just a notation, a representation, of any number; it
        has nothing to do with xor or anything else.  A number can be
        represented in hex, binary, or decimal.  The TOY instruction
        9CFF happens to produce output in hex form.  It has nothing to
        do with where the register R[C] got its value from.

    (b) Xor, as explained at the beginning of problem 10, performs a
        bit-by-bit operation (or so called bit-wise operation).  Since
        any number can be represented by a string of 0s and 1s, you
        can xor two numbers bit-by-bit to produce a third number.
        This third number is just that, a number, which can be
        represented by hex, binary, or decimal representations.
        Again, 9CFF just happens to choose to represent it in hex.

Randy