The document describes four types of flip-flops: SR flip-flop, D flip-flop, JK flip-flop, and T flip-flop. It provides the module definitions for each type, showing their inputs, outputs, and how their next state is determined from the current inputs and state. A D flip-flop module is also included and used by the JK and T flip-flop modules.

1. SR Flip-Flop
D Flip-Flop
JK Flip-Flop
T Flip-Flop

2. SR FLIP-FLOP
module sr_flipflop(s,r,clk,q,qbar);
input s,r,clk;
output q,qbar;
reg q,qbar;
always@(posedge clk)
begin
case ({s,r})
2'b00:q=q;
2'b01:q=1'b0;
2'b10:q=1'b1;
2'b11:q=1'bx;
endcase
qbar=~q;
end
endmodule
D FLIP-FLOP
module D_FF (D,clk,reset,Q);
input D,clk,reset;
output Q;
reg Q;
always @ (posedge reset or negedge clk)
if (reset)
Q = 1'b0;
else
Q = D;
endmodule

3. JK FLIP-FLOP
module JK_FF (J,K,clk,reset,Q);
input J,K,clk,reset;
output Q;
wire w;
assign w = (J&~Q)|(~K&Q);
D_FF dff1(w,clk,reset,Q);
endmodule
module D_FF (D,clk,reset,Q);
input D,clk,reset;
output Q;
reg Q;
always @ (posedge reset or negedge clk)
if (reset)
Q = 1'b0;
else
Q = D;
endmodule
T FLIP-FLOP
module T_FF (T,clk,reset,Q);
input T,clk,reset;
output Q;
wire w;
assign w = T^Q;
D_FF dff1(w,clk,reset,Q);
endmodule
module D_FF (D,clk,reset,Q);
input D,clk,reset;
output Q;
reg Q;
always @ (posedge reset or negedge clk)
if (reset)
Q = 1'b0;
else
Q = D;
endmodule