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in Verilog by (220 points)

How do you code a d flip flop in Verilog?

3 Answers

0 votes
by (220 points)

The D flip-flop actually is a modification of the clocked SR flip-flop. The D input goes into the S input and the inverted D input goes to the R input. The D input is sampled by a clock pulse. If it is 1, the flip-flop is switched to the set state (Q -> 1). If it is 0, the flip-flop switches to the reset state (Q -> 0). In simple terms, the D flip-flop is just the sampled d input by the clock edge.

module dff (
input clk,
input d,
output q,
output qn
);

reg ff;

always @(posedge clk) ff <= d;

assign {q, qn} = {ff, ~ff};

endmodule
0 votes
by (220 points)

It is a basic memory cell that is triggered when an active edge transitions occurs. At the rising or falling edge of the clock signal, depending on the design, the value at the D-input of the flipflop is captured and it appears on the output Q. The value is held until the next transition of the clock. An example code of a postive edge or rising edge D-Flip Flop is shown below (source: https://www.fpga4student.com/2017/02/verilog-code-for-d-flip-flop.html):

module RisingEdge_DFlipFlop(D,clk,Q);
input D; // Data input
input clk; // clock input
output Q; // output Q
always @(posedge clk)
begin
Q <= D;
end
endmodule
The code for the falling edge or negative edge D-Flip Flop is the same except the key word 'posedge' is replaced with 'negedge'.
0 votes
by (220 points)

Here is an example of D_FF with synchronous reset. The reset value is zero by using constant in verilog.

parameter RESET_VALUE = 1'b0;
reg d_ff;
always @(posedge clk)
begin
if(rst) d_ff <= RESET_VALUE;
else d_ff <= in_dat;
end

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