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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 dffsr
( input d, clk, pre, clr, output reg q );
initial begin
q = 0;
end
always @( posedge clk, posedge pre, posedge clr )
if ( clr )
q <= 1'b0;
else if ( pre )
q <= 1'b1;
else
q <= d;
endmodule
module ndffnsnr
( input d, clk, pre, clr, output reg q );
initial begin
q = 0;
end
always @( negedge clk, negedge pre, negedge clr )
if ( !clr )
q <= 1'b0;
else if ( !pre )
q <= 1'b1;
else
q <= d;
endmodule
module top (
input clk,
input clr,
input pre,
input a,
output b,b1,b2,b3
);
dffsr u_dffsr (
.clk (clk ),
.clr (clr),
.pre (pre),
.d (a ),
.q (b )
);
ndffnsnr u_ndffnsnr (
.clk (clk ),
.clr (clr),
.pre (pre),
.d (a ),
.q (b1 )
);
adff u_adff (
.clk (clk ),
.clr (clr),
.d (a ),
.q (b2 )
);
adffn u_adffn (
.clk (clk ),
.clr (clr),
.d (a ),
.q (b3 )
);
endmodule
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