Code: Select all

module kbd

	(input kbd_clk, kbd_data,
	output reg [7:0] scan = 0, output reg scan_ready = 0);
	
	parameter start_bit = 0;
	parameter receive_data = 1;
	parameter parity = 2;
	parameter stop_bit = 3;
		
	reg [7:0] rxdata = 8'd0;
	reg [3:0] bitcounter = 4'd0;
	reg [1:0] state = 2'd0;
	
	wire kbdclk;
	wire kbddata;
		
	assign kbdclk = kbd_clk;
	assign kbddata = kbd_data;
	
	always @(negedge kbdclk) begin
	
		case(state)
	
			start_bit: begin
		
				if (kbddata == 1'b1) state = start_bit;
				else begin
				
					state <= receive_data;
					scan_ready <= 1'b0;
					rxdata <= 8'd0;
					bitcounter <= 0;
										
				end
		
			end
			
			receive_data: begin
			
				if (bitcounter == 4'b1000) begin
					
					state <= parity;
					bitcounter <= 4'd0;
								
				end else begin
				
					bitcounter <= bitcounter + 1;
					rxdata <= {kbddata,rxdata[7:1]};
					
				end
				
			end
			
			parity: state <= stop_bit;
									
			stop_bit: begin
			
				if (kbddata == 1'b1) begin
										
					scan = rxdata;
					scan_ready <= 1'b1;
					state = start_bit;
					
				end else state <= start_bit;
							
			end
			
			default: state <= start_bit;
	
		endcase
	
	end
	
endmodule 

Code: Select all

`timescale 1us/1ns

module tb;

	reg kbdclk;
	reg kbddata;
	wire [7:0] scan;
	wire scan_ready;

	integer i;
	reg [10:0] frame;

	kbd dut (
		.kbd_clk(kbdclk),
		.kbd_data(kbddata),
		.scan(scan),
		.scan_ready(scan_ready)
    );

    task send_bit(input reg b);
		
		begin
		
			kbddata = b;   
			#5;
			kbdclk = 0;    
			#5;
			kbdclk = 1;
			#5;
    
		end
    
	 endtask

    initial begin
        
		kbdclk = 1;
		kbddata = 1;

		frame[0]  = 1'b0;
		frame[1]  = 1'b1;
		frame[2]  = 1'b0;
		frame[3]  = 1'b1;
		frame[4]  = 1'b0;
		frame[5]  = 1'b1;
		frame[6]  = 1'b0;
		frame[7]  = 1'b1;
		frame[8]  = 1'b0;
		frame[9]  = 1'b1;
		frame[10] = 1'b1;

		#20;

		for (i = 0; i < 11; i = i + 1) send_bit(frame[i]); #50;

	end

    initial begin
        $monitor("t=%0t kbdclk=%b kbddata=%b scan=%b scan_ready=%b state=%0d bitcounter=%0d rxdata=%b",
                 $time, kbdclk, kbddata, scan, scan_ready,
                 dut.state, dut.bitcounter, dut.rxdata);
    end

endmodule