Lesson 4 of 5

Dim an LED on the Arduino header

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// PWM on Arduino pin D3: the switches set the brightness, or SW9 makes it breathe. module top #( parameter CLK_HZ = 50_000_000 ) ( input MAX10_CLK1_50, input [9:0] SW, // SW7-SW0: brightness 0-255; SW9: breathe output [15:0] ARDUINO_IO, // the Arduino header, D0-D15 (D3 is bit 3) output [9:0] LEDR ); // Breathing: level climbs to 255 and back, one step every STEP clocks. localparam STEP = CLK_HZ / 256; reg [31:0] tick = 0; reg [7:0] level = 0; reg up = 1'b1; always @(posedge MAX10_CLK1_50) begin if (tick == STEP - 1) begin tick <= 0; if (up) begin if (level == 8'd255) up <= 1'b0; else level <= level + 1; end else begin if (level == 8'd0) up <= 1'b1; else level <= level - 1; end end else tick <= tick + 1; end // SW9 up: follow the breath; down: the switches. wire [7:0] duty = SW[9] ? level : SW[7:0]; // PWM: high while a free-running 8-bit ramp is below duty. reg [7:0] ramp = 0; always @(posedge MAX10_CLK1_50) ramp <= ramp + 1; wire bright = ramp < duty; assign ARDUINO_IO = {12'b0, bright, 3'b000}; // only D3 is driven; the rest stay low assign LEDR = {SW[9], 8'b0, bright}; endmodule

Stopped · Your code isn't running yet. Until you press Run, the board runs the program already on it.

Nothing printed yet. Press Run.

SW7-SW0 set the brightness of an LED on Arduino pin D3, 0 to 255 out of 256. Flip SW9 and it breathes by itself, fading up and down every two seconds.

A counter and a comparator make PWM
A second counter makes it breathe
Any FPGA pin can do PWM

iynk runs your Verilog as a behavioural model, cycle by cycle on the board clock. It does not synthesise, place or route: no timing, no LUT counts.

Pin	Connects to	What it does
`D3`	R1 220 Ω → LED anode	The PWM output, ARDUINO_IO[3]
`GND`	LED cathode (GND on JP2)	The return path
`SW9`	PIN_F15 (SW[9])	Up: breathe; down: SW7-SW0 set the level

Wire it in

Sensors and actuators this board drives, with the real connections.

LEDSupply 3.3 V
Anode to D3 through 220 Ω, cathode to GND. Drive it from your design like any LEDR.
Part pin Board pin
A D3Wire colour orange
K GNDWire colour black
Careful
A pin gives 8 mA at most: always fit the resistor.

Part pin	Board pin
A	D3Wire colour orange
K	GNDWire colour black

All 7 parts on the Terasic DE10-Lite page

Dim an LED on the Arduino header

Try it yourself

Serial monitor

Checks

Break it

Inputs

Wire it in

Dim an LED on the Arduino header

Try it yourself

Serial monitor

Checks

Break it

Inputs

Wire it in