Verilog 灰色计数器
设计
module gray_ctr
# (parameter N = 4)
( input clk,
input rstn,
output reg [N-1:0] out);
reg [N-1:0] q;
always @ (posedge clk) begin
if (!rstn) begin
q <= 0;
out <= 0;
end else begin
q <= q + 1;
`ifdef FOR_LOOP
for (int i = 0; i < N-1; i= i+1) begin
out[i] <= q[i+1] ^ q[i];
end
out[N-1] <= q[N-1];
`else
out <= {q[N-1], q[N-1:1] ^ q[N-2:0]};
`endif
end
end
endmodule
测试台
module tb;
parameter N = 4;
reg clk;
reg rstn;
wire [N-1:0] out;
gray_ctr u0 ( .clk(clk),
.rstn(rstn),
.out(out));
always #10 clk = ~clk;
initial begin
{clk, rstn} <= 0;
$monitor ("T=%0t rstn=%0b out=0x%0h", $time, rstn, out);
repeat(2) @ (posedge clk);
rstn <= 1;
repeat(20) @ (posedge clk);
$finish;
end
endmodule
模拟日志ncsim> run T=0 rstn=0 out=0xx T=10 rstn=0 out=0x0 T=30 rstn=1 out=0x0 T=50 rstn=1 out=0x1 T=70 rstn=1 out=0x3 T=90 rstn=1 out=0x2 T=110 rstn=1 out=0x6 T=130 rstn=1 out=0x7 T=150 rstn=1 out=0x5 T=170 rstn=1 out=0x4 T=190 rstn=1 out=0xc T=210 rstn=1 out=0xd T=230 rstn=1 out=0xf T=250 rstn=1 out=0xe T=270 rstn=1 out=0xa T=290 rstn=1 out=0xb T=310 rstn=1 out=0x9 T=330 rstn=1 out=0x8 T=350 rstn=1 out=0x0 T=370 rstn=1 out=0x1 T=390 rstn=1 out=0x3 T=410 rstn=1 out=0x2 Simulation complete via $finish(1) at time 430 NS + 0
Verilog