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module adff
( input d, clk, clr, output reg q );
initial begin
q = 0;
end
always @( posedge clk, posedge clr )
if ( clr )
q <= 1'b0;
else
q <= d;
endmodule
module adffn
( input d, clk, clr, output reg q );
initial begin
q = 0;
end
always @( posedge clk, negedge clr )
if ( !clr )
q <= 1'b0;
else
q <= d;
endmodule
module dffs
( input d, clk, pre, clr, output reg q );
initial begin
q = 0;
end
always @( posedge clk )
if ( pre )
q <= 1'b1;
else
q <= d;
endmodule
module ndffnr
( input d, clk, pre, clr, output reg q );
initial begin
q = 0;
end
always @( negedge clk )
if ( !clr )
q <= 1'b0;
else
q <= d;
endmodule
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