VLSI: 4 Bit Full Adder with Carry Select Dataflow Modelling with Testbench
Verilog Code for 4 Bit Full Adder with Carry Select Dataflow Modelling
module FACS(
input [3:0]x,cin,
input [3:0]y,
output [3:0]s,
output cout,
);
//for carry '0'
fa f0(a0,c0,0,x[0],y[0]);
fa f1(a1,c1,c0,x[1],y[1]);
fa f2(a2,c2,c1,x[2],y[2]);
fa f3(a3,c3,c2,x[3],y[3]);
//for carry '1'
fa f4(a4,c4,1,x[0],y[0]);
fa f5(a5,c5,c4,x[1],y[1]);
fa f6(a6,c6,c5,x[2],y[2]);
fa f7(a7,c7,c6,x[3],y[3]);
//two:one MUX
mux
m0(s[0],cin,a0,a4);
mux
m1(s[1],cin,a1,a5);
mux
m2(s[2],cin,a2,a6);
mux
m3(s[3],cin,a3,a7);
mux
m4(cout,cin,c7,c3);
endmodule
//full adder
module fa(sum,carry,a,b,c4);
output sum,carry;
input a,b,c4;
assign p = (a^b);
assign r = a & b;
assign sum = p ^ c4;
assign q = p ^ c4;
assign carry = q ^ r;
endmodule
//mux
module mux(
output Y,
input D0, D1, S, );
assign T1 = D1 & S;
assign T2 = D0 & Sbar;
assign Sbar = ~ S;
assign Y = T1 | T2;
endmodule
//Testbench code for 4 Bit Full Adder with Carry Select Dataflow Modelling
initial begin
//
Initialize Inputs
x
= 0;y = 0;cin = 0;
// Wait 100
ns for global reset to finish
#100;
// Add
stimulus here
#100;x
= 0;y = 0;cin = 1;
#100;x
= 0;y = 1;cin = 0;
#100;x
= 0;y = 1;cin = 1;
#100;x
= 1;y = 0;cin = 0;
#100;x
= 1;y = 0;cin = 1;
#100;x
= 1;y = 1;cin = 0;
#100;x
= 1;y = 1;cin = 1;
end
Output:
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