Full Adder HW Question

[LilGreekKid]

Full Adder HW Question - Just need to know if I am doing this correctly

Q: Determine the outputs for the circuit shown below. Assume that C0 = 0 for all cases. (attached is the circuit and waveform)

I know how to calculate full adder and half adder. But with this problem, do I figure out what A and B is for each column? For instance first column
A1 = 0
A2 = 1
A3 = 0
A4 = 1

B1 = 0
B2 = 1
B3 = 0
B4 = 1

1010
+ 1010
----------
10100

s1 = 0 (Low)
s2 = 0 (Low)
s3 = 1 (High)
s4 = 0 (Low)
c4 = 1 (High) <--Carry

I am just wondering if this is how it is supposed to be done and I draw the s1,s2,s3,s4 on the graph?

 

[fouadalnoor]

Well from what I see S1,S2,S3 are all low as is shown on the graph. Not so sure about the C4 though. I dont know if its just related to A4 and B4 or not..

 

[MrAl]

Hi,

It looks like they want you to look at the graph for A and B to first determine the inputs, then using those inputs draw s1 through s4 and C4 as you did for the 2nd set of inputs which was 10 plus 10. The first set is 0 plus 0, the second set 10 plus ten as you did, and the third set is 3 plus 3. You should draw a line higher when the output of that s is a 1 and a line lower when the output of that s is a 0. Right now they show all the s being low so you have to change that.

 

[fouadalnoor]

Hi,

It looks like they want you to look at the graph for A and B to first determine the inputs, then using those inputs draw s1 through s4 and C4 as you did for the 2nd set of inputs which was 10 plus 10. The first set is 0 plus 0, the second set 10 plus ten as you did, and the third set is 3 plus 3. You should draw a line higher when the output of that s is a 1 and a line lower when the output of that s is a 0. Right now they show all the s being low so you have to change that.

Ah so his C4 is related to A4 and B4?

 

[MrAl]

Hi again,

Well C4 is the carry out so if the two four bit numbers add up to more than 15 there will be a carry signal too.
With no carry we'd get 01001 for '9' for example if we added 4+5, but if we added 8+9 we'd get 10001 (17 decimal) where the carry is now a 1.