ECE 275: Digital Design I
Class 10Adders!!!!
Full Adder
S = A'B'Cin + A'BCin' + AB'Cin' + ABCin S = A'(B â Cin) + A(B â Cin)' S = A â B â Cin
Cout = A'BCin + AB'Cin + ABCin' + ABCin Cout = Cin(A'B + AB') + AB(Cin' + Cin) Cout = Cin(A â B) + AB Other forms Cout = AB + Cin(A + B) Cout = AB + BCin + ACin
Form 1
Form 2
Form 3
Would prefer From 3 because it will be be fastest due to Critical Path (the longest path it takes for something to get the result)
Design Problem 1
How do design a full adder using half adders
Design Problem 2
A: A3 A2 A1 A0 B: B3 B2 B1 B0
4-bit Adder
A3 A2 A1 A0 B3 B2 B1 B0 FA <- FA <- FA <- HA S3 S2 S1 S0 Cout
4-bit RCA (Ripple Carry Adder) CLA (Carry Lookahead Adder)
Design Problem 3
Find the 2's Complement of a 4bit number