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输入和输出
- 时钟信号 clk
- 复位信号 reset
- rgb三颜色输出 [2:0] r,g, [1:0] b
- 行信号输出 hs
- 列信号输出 vs
参数设定
设定边界，决定改变方向与否
parameter UP_BOUND = 31;
parameter DOWN_BOUND = 510;
parameter LEFT_BOUND = 144;
parameter RIGHT_BOUND = 783;状态机决定下一次扫描输出的颜色
parameter S0 = 2'b00, S1 = 2'b01, S2 = 2'b10, S3 = 2'b11;
reg [2:0] state, nextstate;
reg [2:0] nextr, nextg;
reg [1:0] nextb;程序处理
行信号和列信号的处理
行信号和列信号决定着当前像素是否显示出来。该程序选择的是在25Hz下640 * 480的分辨率显示。具体想改变分辨率的，可以在参考网上的资料。VGA的显示是逐行扫描像素点，除了可见区域，还有不可见区域的像素点，因此可以通过边界控制是否输出。
wire myclk;
reg [1:0] count;
reg [9:0] hcount, vcount;
assign myclk = count[1];
always@(posedge clk)
begin
if(reset)
count <= 0;
else
count <= count + 1'b1;
end
assign hs = (hcount < 96) ? 1'b0 : 1'b1;
always@(posedge myclk or posedge reset)
begin
if(reset)
hcount <= 0;
else if(hcount == 799)
hcount <= 0;
else
hcount <= hcount + 1'b1;
end
assign vs = (vcount < 2) ? 1'b0 : 1'b1;
always@(posedge myclk or posedge reset)
begin
if(reset)
vcount <= 0;
else if(hcount == 799)
begin
if(vcount == 520)
vcount <= 0;
else
vcount <= vcount + 1'b1;
end
else
vcount <= vcount;
end颜色持续变换形成彩色轮变
彩色变化，通过状态机实现。每一列像素点对应一个颜色，但是方块区域才通过彩色输出，否则输出黑色，形成了彩色轮转。
always@(posedge myclk or posedge reset)
begin
if(reset)
begin
r <= 0;
g <= 0;
b <= 0;
end
else begin
if((vcount >= up_pos)
&& (vcount <= down_pos)
&& (hcount >= left_pos)
&& (hcount<=right_pos))
begin
r <= nextr;
g <= nextg;
b <= nextb;
end
else
begin
r <= 3'b000;
g <= 3'b000;
b <= 2'b00;
end
end
end
always@(posedge myclk or posedge reset)
begin
if(reset)
state <= S0;
else
state <= nextstate;
end
always@(*)
begin
case(state)
S0: nextstate <= S1;
S1: nextstate <= S2;
S2: nextstate <= S3;
S3: nextstate <= S0;
default: nextstate <= S0;
endcase
end
always@(*)
begin
case(state)
S0: begin nextr <= 3'b111; nextg <= 3'b000; nextb <= 2'b00; end
S1: begin nextr <= 3'b000; nextg <= 3'b111; nextb <= 2'b00; end
S2: begin nextr <= 3'b000; nextg <= 3'b000; nextb <= 2'b11; end
S3: begin nextr <= 3'b111; nextg <= 3'b111; nextb <= 2'b00; end
default: begin nextr <= 3'b111; nextg <= 3'b000; nextb <= 2'b11; end
endcase
end信号处理
但列信号由输出变成非输出时触发。在这个情况下，应该处理下一帧的方向和速度。详见代码。
always@(negedge vs or posedge reset)
begin
if(reset)
begin
h_speed <= 1;
v_speed <= 0;
end
else
begin
if(up_pos == UP_BOUND)
v_speed <= 1;
else if(down_pos == DOWN_BOUND)
v_speed <= 0;
else
v_speed <= v_speed;
if (left_pos == LEFT_BOUND)
h_speed <= 1;
else if (right_pos == RIGHT_BOUND)
h_speed <= 0;
else
h_speed <= h_speed;
end
end
always@(posedge vs or posedge reset)
begin
if(reset)
begin
up_pos <= 391;
down_pos <= 510;
left_pos <= 384;
right_pos <= 543;
end
else
begin
if(v_speed)
begin
up_pos <= up_pos + 1'b1;
down_pos <= down_pos + 1'b1;
end
else
begin
up_pos <= up_pos - 1'b1;
down_pos <= down_pos - 1'b1;
end
if(h_speed)
begin
left_pos <= left_pos + 1'b1;
right_pos <= right_pos + 1'b1;
end
else
begin
left_pos <= left_pos - 1'b1;
right_pos <= right_pos - 1'b1;
end
end
end完整代码
//main.v
`timescale 1ns / 1ps
module VGA(
input clk,
input reset,
output reg [2:0] r,
output reg [2:0] g,
output reg [1:0] b,
output hs,
output vs
);
parameter UP_BOUND = 31;
parameter DOWN_BOUND = 510;
parameter LEFT_BOUND = 144;
parameter RIGHT_BOUND = 783;
parameter S0 = 2'b00, S1 = 2'b01, S2 = 2'b10, S3 = 2'b11;
reg [2:0] state, nextstate;
reg [2:0] nextr, nextg;
reg [1:0] nextb;
reg h_speed, v_speed;
reg [9:0] up_pos, down_pos, left_pos, right_pos;
wire myclk;
reg [1:0] count;
reg [9:0] hcount, vcount;
assign myclk = count[1];
always@(posedge clk)
begin
if(reset)
count <= 0;
else
count <= count + 1'b1;
end
assign hs = (hcount < 96) ? 1'b0 : 1'b1;
always@(posedge myclk or posedge reset)
begin
if(reset)
hcount <= 0;
else if(hcount == 799)
hcount <= 0;
else
hcount <= hcount + 1'b1;
end
assign vs = (vcount < 2) ? 1'b0 : 1'b1;
always@(posedge myclk or posedge reset)
begin
if(reset)
vcount <= 0;
else if(hcount == 799)
begin
if(vcount == 520)
vcount <= 0;
else
vcount <= vcount + 1'b1;
end
else
vcount <= vcount;
end
always@(posedge myclk or posedge reset)
begin
if(reset)
begin
r <= 0;
g <= 0;
b <= 0;
end
else begin
if((vcount >= up_pos)
&& (vcount <= down_pos)
&& (hcount >= left_pos)
&& (hcount<=right_pos))
begin
r <= nextr;
g <= nextg;
b <= nextb;
end
else
begin
r <= 3'b000;
g <= 3'b000;
b <= 2'b00;
end
end
end
always@(posedge myclk or posedge reset)
begin
if(reset)
state <= S0;
else
state <= nextstate;
end
always@(*)
begin
case(state)
S0: nextstate <= S1;
S1: nextstate <= S2;
S2: nextstate <= S3;
S3: nextstate <= S0;
default: nextstate <= S0;
endcase
end
always@(*)
begin
case(state)
S0: begin nextr <= 3'b111; nextg <= 3'b000; nextb <= 2'b00; end
S1: begin nextr <= 3'b000; nextg <= 3'b111; nextb <= 2'b00; end
S2: begin nextr <= 3'b000; nextg <= 3'b000; nextb <= 2'b11; end
S3: begin nextr <= 3'b111; nextg <= 3'b111; nextb <= 2'b00; end
default: begin nextr <= 3'b111; nextg <= 3'b000; nextb <= 2'b11; end
endcase
end
always@(negedge vs or posedge reset)
begin
if(reset)
begin
h_speed <= 1;
v_speed <= 0;
end
else
begin
if(up_pos == UP_BOUND)
v_speed <= 1;
else if(down_pos == DOWN_BOUND)
v_speed <= 0;
else
v_speed <= v_speed;
if (left_pos == LEFT_BOUND)
h_speed <= 1;
else if (right_pos == RIGHT_BOUND)
h_speed <= 0;
else
h_speed <= h_speed;
end
end
always@(posedge vs or posedge reset)
begin
if(reset)
begin
up_pos <= 391;
down_pos <= 510;
left_pos <= 384;
right_pos <= 543;
end
else
begin
if(v_speed)
begin
up_pos <= up_pos + 1'b1;
down_pos <= down_pos + 1'b1;
end
else
begin
up_pos <= up_pos - 1'b1;
down_pos <= down_pos - 1'b1;
end
if(h_speed)
begin
left_pos <= left_pos + 1'b1;
right_pos <= right_pos + 1'b1;
end
else
begin
left_pos <= left_pos - 1'b1;
right_pos <= right_pos - 1'b1;
end
end
end
endmodule