Fall 2007       QUIZ 1

MA 240   2-bit ADDER TRUTH TABLE                Name:  ________________________

Fill out the truth table (meaning the columns for the three sum bits:  s2, s1, and s0, where s0 is the low order bit, and in general si is the column for 2i).

(See below for example of 2-bit binary addition, with carries.)  Just the truth table!  (No need to include boolean expressions or circuits.)

 a

b

     a+b = s

a1a0        

+ b1b0      

----------      

s2s1s0      

a1 a0 b1 b0   s2 s1 s0
0 0 0 0        
0 0 0 1        
0 0 1 0        
0 0 1 1        
0 1 0 0        
0 1 0 1        
0 1 1 0        
0 1 1 1        
1 0 0 0        
1 0 0 1        
1 0 1 0        
1 0 1 1        
1 1 0 0        
1 1 0 1        
1 1 1 0        
1 1 1 1        

  Example of two-bit binary addition, with two carries:

 

 0 1
+   1 1
----------
 

 

 

 00 1
+   1 1
----------

0

 
 

 1 0 1
+   1 1
----------
0 0

  0 1
+   1 1
----------
1 0 0

(superscripted numerals are carry bits from column to the left)