Thursday, September 17, 2009 12:52 AM,

A student writes:



	Professor, I don't understand where the carry in value 
	of 1 is coming from on the second line of the truth table 
	for a 2 bit full adder.

	A    B   CarryIn   |  Carry Out    Sum
        -------------------|-------------------
	0    0      0      |     0          0
	0    0      1      |     0          1

	Thanks for your time,
	<<name withheld to protect the student who can't find the carry in>>




It is the carry out of the previous bit position.  Look at Figure 3.16 in the 
text book.

This is the case for all bit positions EXCEPT the right-most bit.
For the right-most bit, the carry in is 0, so that input combination can not 
occur.

Good luck finishing Problem set 2.  And, please note that we did not get to a 
couple of topics yet, so they have been removed from problem set 2 and moved 
to problem set 3.

Yale Patt