點(diǎn)亮或熄滅LED

　　下面是如何讓LED閃爍的代碼(開(kāi)/關(guān)).

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　　module LEDblink(clk, LED);input clk; // clock typically from 10MHz to 50MHzoutput LED;// create a binary counterreg [32:0] cnt;always @(posedge clk) cnt<=cnt+1;assign LED = cnt[22]; // blink the LED at a few Hz (change

　　// the bit index to change the blinking rate)endmodule====================================================

　　使LED半亮

　　一種辦法是增大串聯(lián)在LED的電阻的阻值一倍。

　　另一種辦法是通過(guò)FPGA驅(qū)動(dòng)LED一半的時(shí)間。如果切換的速度足夠快的話，LED看

　　起來(lái)就是半亮的。

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　　module LEDhalflit(clk, LED);input clk; // clk should be at least 200Hz. Anything above

　　//is fine (most FPGA boards have adequate clocks,

　　// running at a few 10's of MHz)output LED;reg toggle;always @(posedge clk) toggle<=~toggle;

　　// toggles at half

　　//the clk frequency

　　// (at least 100Hz)assign LED = toggle;endmodule====================================================

　　平滑的改變LED的亮度

　　對(duì)于LED亮度控制。PWM信號(hào)是一個(gè)理想的解決辦法。

　　下面是使用4位數(shù)字來(lái)控制LED產(chǎn)生16個(gè)亮度等級(jí)的例子。

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　　module LED_PWM(clk, PWM_input, LED);input clk;input [3:0] PWM_input;

???????????????????????????????????????????????????????? // 16 intensity levelsoutput LED;reg [4:0] PWM;always @(posedge clk) PWM <= PWM[3:0]+PWM_input;assign LED = PWM[4];endmodule=====================

　　LED呼吸閃爍

　　通過(guò)連續(xù)的改變LED的亮度，使得LED看起來(lái)像是在呼吸。

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　　module LEDglow(clk, LED);input clk;output LED;reg [23:0] cnt;always @(posedge clk) cnt<=cnt+1;wire [3:0] PWM_input = cnt[23] ? cnt[22:19] : ~cnt[22:19];

　　// ramp the PWM input up and downreg [4:0] PWM;always @(posedge clk) PWM <= PWM[3:0]+PWM_input;assign LED = PWM[4];endmodule====================================================

　　這跟我們?cè)诘谝还?jié)展示的例子的HDL代碼是一樣的.