In this exampel we count up to 256 each time we press the increase button and show the bianry result using 8 LEDs. My FPGA, Cyclone IV board has a 50MHz clock. We will ahve to make a crude debounce and count up to 40ms (2 millions pulses from clock) after each button press so we make sure there are no oscillations. Then we increase the counter register by one and the 8 bit LEDs will cahnge their value since those are connected to each bit of that register. Below, you have the entire project ready to downlaod. Open it in Quartus and create the synthesis for your FPGA.
//We create the module with 3 inputs, and one 8-bit output for 8 LEDs
module counter (clk, button, reset, LEDS);
//Define inputs and outputs
input clk, button, reset;
output [7:0]LEDS;
//Create register for counting the amount of times the button was pressed
reg [7:0] count;
//3 more registers used for debounce since the button will oscillate a few times when pressed
reg [24:0]counter_pressed, counter_not_pressed;
reg button_state = 1'b1;
//Give initial values to the registers. It's important otherwise there might be errors
initial begin
count <= 8'b0;
counter_pressed <= 25'b0;
counter_not_pressed <= 25'b0;
end
//Each positive edge of the clock (50MHz in this case), we enter this part of code
always @ (posedge clk or negedge reset)
begin
if(!reset)//If the reset is negative (reset button pressed) we reset the valeus
begin
count <= 8'b0;
counter_pressed<= 25'b0;
counter_not_pressed<= 25'b0;
end
else
begin
//If button is negative (button pressed) and status is low we start counting
if(!button & !button_state)
begin
counter_pressed <= counter_pressed + 1'b1; //Counting
end
else
begin
counter_pressed <= 25'b0; //If not, reset the counter
end
if(counter_pressed == 25'd2000000)//When 2M pulses are reached, we increase the push counter by one and reset the others
begin
count = count + 1'b1;
counter_pressed <= 25'b0;
button_state = 1'b1;
end
//Do the same for the positive part of button (button not pressed)
if(button & button_state)
begin
counter_not_pressed <= counter_not_pressed + 1'b1;
end
else
begin
counter_not_pressed <= 25'b0;
end
if(counter_not_pressed == 25'd2000000)
begin
counter_not_pressed <= 25'b0;
button_state = 1'b0;
end
end//end of else of negative reset
end//end of always
//Finally, assign 8 bits from the counter to the 8 LEDs
assign LEDS[7:0] = count[7:0];
endmodule
