=Electronics Hardware Questions=

Q: Implement a comparator using combinational logic, that compares two 2-bit numbers A and B. The comparator should have 3 outputs: A > B, A < B, A = B.


A1	A0	B1	B0	A>B	B>A	A=B
---------------------------------------------------
0	0	0	0	0	0	1
0	0	0	1	0	1	0
0	0	1	0	0	1	0
0	0	1	1	0	1	0
0	1	0	0	1	0	0
0	1	0	1	0	0	1
0	1	1	0	0	1	0
0	1	1	1	0	1	0
1	0	0	0	1	0	0
1	0	0	1	1	0	0
1	0	1	0	0	0	1
1	0	1	1	0	1	0
1	1	0	0	1	0	0
1	1	0	1	1	0	0
1	1	1	0	1	0	0
1	1	1	1	0	0	1

Here is the behavioral model of the comparator in verilog:

module comp0 (y1,y2,y3,a,b);
 input [1:0] a,b;
 output y1,y2,y3;
 wire y1,y2,y3;

 assign y1= (a >b)? 1:0;
 assign y2= (b >a)? 1:0;
 assign y3= (a==b)? 1:0; 
 
endmodule

The gate level model:

module comp0 (y1,y2,y3,a,b);
 input [1:0] a,b;
 output y1,y2,y3;
 wire y1,y2,y3;
 wire xor1_out,xor2_out,nand1_out,nand2_out,nand3_out,nand4_out,or1_out,or2_out;
 
 xor  xor1 (xor1_out,a[0],b[0]);
 xor  xor2 (xor2_out,a[1],b[1]);
 nand nand1(nand1_out,a[0],xor1_out);
 nand nand2(nand2_out,b[0],xor1_out); 
 nand nand3(nand3_out,a[1],xor2_out); 
 nand nand4(nand4_out,b[1],xor2_out);  
 nand nand5(y1,or1_out,nand3_out); 
 nand nand6(y2,or2_out,nand4_out); 
 or   or1  (or1_out,nand1_out,xor1_out);
 or   or2  (or2_out,nand2_out,xor1_out);  
 nor  nor1 (y3,xor1_out,xor2_out);
 
endmodule