I am having a little trouble understand two's complement. I kind of get the general idea. What I don't get is why an overflow occurs here? 1100 1000 which is 100+100 does in fact equal 200.... Can someone please explain this to me?

Thanks.... (The problem below was copied from my notes from class)

0110 0100 = +100

+ 0110 0100 = +(+100)

-------------------

1100 1000 = -56

WRONG! Carry into MSB is 1 and carry out of MSB is 0. Overflow condition occurs!