Flip-Flop's

An RS Flip-Flop

module srff(s,r,q,qb); 

input s,r; 

output q,qb; 

wire ss,rr; 

not(ss,s),(rr,r);

nand(q,ss,qb);

nand(qb,rr,q);

endmodule

module tstsrff; //test-bench 

reg s,r; 

wire q,qb; 

srff ff(s,r,q,qb); 

initial

begin

s =1'b1; 

r =1'b0; 

end

always

begin

#2 s =1'b0;r =1'b0; 

#2 s =1'b0;r =1'b1; 

#2 s =1'b0;r =1'b0; 

#2 s =1'b1;r =1'b0; 

#2 s =1'b0;r =1'b0; 

end

initial $monitor($time, " s = %b, r = %b, q = %b, qb = %b ",s,r,q,qb); 

initial #20 $stop; 

endmodule

Clocked RS Flip-Flop

module srffcplev(cp,s,r,q,qb);

input cp,s,r; 

output q,qb; 

wire ss,rr; 

nand(ss,s,cp),(rr,r,cp),(q,ss,qb),(qb,rr,q);

endmodule

module srffcplev_tst;// test-bench 

reg cp,s,r; 

wire q,qb; 

srffcplev ff(cp,s,r,q,qb); 

initial

begin

cp=1'b0;

s =1'b1; 

r =1'b0; 

end

always #2cp=~cp; 

always

begin

#4 s =1'b0;r =1'b0; 

#4 s =1'b0;r =1'b1; 

#4 s =1'b0;r =1'b0; 

#4 s =1'b1;r =1'b0; 

#4 s =1'b0;r =1'b0; 

end

initial $monitor($time,"cp = %b ,s = %b , r = %b , q = %b , qb = %b " ,cp,s,r,q,qb); 

initial #20 $stop; 

endmodule

D-Latch

module dlatch(en,d,q,qb); 

input d,en; 

output q,qb; 

wire dd; 

wire s,r; 

not n1(dd,d); 

nand (sb,d,en); 

nand g2(rb,dd,en);

sbrbff ff(sb,rb,q,qb);//Instantiation of the sbrbff

endmodule

module tstdlatch; //test-bench 

reg d,en; 

wire q,qb; 

dlatch ff(en,d,q,qb); 

initial

begin

d = 1'b0; 

en = 1'b0; 

end

always #4 en =~en; 

always #8 d=~d; 

initial $monitor($time," en = %b , d = %b , q = %b , qb= %b " , en,d,q,qb); 

initial #40 $stop; 

endmodule