// This is a 4-bit counter
// that can either count up or down (depending on a switch)
// and that counts up/down roughly every second.

// The purpose of the example is to show how "human-type" speeds
// can be achieved in circuits, even though they use very fast clocks
// e.g. the 50 MHz clock on the DE2 board.

// Author janders; November 2009

module slowcounter(clk, sw0, count4);
	input clk;
	input sw0;
	output reg [3:0] count4;
	reg [24:0] counter;
	reg enable;

        // you need to tie the clk pin to the 50 MHz clock on the DE2 board
        // you need to tie the count4 outputs to the LEDs on the DE2
        // you need to tie the sw0 to one of the switches on the DE2
        
	// generate an enable signal
	always@(posedge clk)
	begin
		counter = counter + 1'b1;
		if (counter == 25'h000000)
			enable = 1'b1;
		else
			enable = 1'b0;
	end
	
	// generate an up/down counter
	always@(posedge clk) 
	begin
		if (enable == 1'b1) 
		begin
	
			if (sw0 == 1'b0)
				count4 = count4 + 1'b1;
			else
				count4 = count4 - 1'b1;
		end
	end	
	
endmodule