Lorick <PICLIST@MITVMA.MIT.EDU> wrote:

> I'm trying to figure out of my 24 bit adder is simulating properly
> but I can't seem to get my binary skills straight with carry and
> all that so I don't really know if I'm doing it properly by hand.
>
> Here's what I'm putting through the simulation:
>
> Number 1:    00000000 11111111 11111111
> Number 2:    01100100 11111111 11111111
>
> The simulator gives out the 24 bit result:
>                     01100110 00000010 11111101
>
> I'm trying to decide if this is correct.  So I guess first, is it
> correct?

    No, it's not correct.

> Then, how DOES it work by hand again? I think I have the basics,
> 1+1=10, 1+0=1 0+0=0  etc....but....I can't make it work in my head.

    It's REAL simple:

        0 + 0 = 0
        0 + 1 = 1
        1 + 0 = 1
        1 + 1 = 10 (or, in other words, 1 + 1 = 0 with a carry)
    1 + 1 + 1 = 11 (or, in other words, 1 + 1 + 1 = 1 with a carry)

    And by the way... You don't need to do BINARY addition to test
    your program's results; instead, just convert the two inputs to
    decimal, add them, then convert the result back to binary.  In
    your case, it works out to:

        65535 + 6619135 = 6684670

        6684670 dec = 01100101 11111111 11111110 bin

    -Andy


=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - San Diego, California
=== http://www.geocities.com/SiliconValley/2499