module pwm_led
  (
  input            clk_50,          // 50 MHz clock op MAX II board
  output reg       max_led,         // led op MAX II board actief low
  input            encoder_A,       // rotary encoder A kanaal
  input            encoder_B        // rotary encoder B kanaal
  );
reg [7:0]  prescaler;               // 50 MHz mag gerust gedeeld worden
reg [7:0]   pwm_teller;             // 8 bit pwm teller
reg [7:0]   pwm_waarde;             // 8 bit pwm teller
reg [2:0]   encoder_A_reg;          // synchronisatie A kanaal
reg [2:0]   encoder_B_reg;          // synchronisatie B kanaal
reg         enc_ena;                // actief bij een flankwissel van A of B
reg 	 	richting2;              // draairichting encoder

assign      pwm_clk = prescaler[7]; // prescaler is 8 bit voor deze pwm_clk

always @ (posedge clk_50)           // delen de clock door 65536
begin
prescaler <= prescaler + 1;
end

always @(posedge pwm_clk)
begin
 encoder_A_reg <= {encoder_A_reg[1:0], encoder_A};  // rotary encoder_A doorschuiven
 encoder_B_reg <= {encoder_B_reg[1:0], encoder_B};  // rotary encoder_B doorschuiven
 enc_ena       <= encoder_A_reg[1] ^ encoder_A_reg[2] ^ encoder_B_reg[1] ^ encoder_B_reg[2];
 richting2     <= encoder_A_reg[1] ^ encoder_B_reg[2];
  if(enc_ena)
   begin 
    if (richting2)
      begin
        if(pwm_waarde < 255)  pwm_waarde <= pwm_waarde +1; // increment tot max 255
      end
    else
      begin
        if (pwm_waarde > 0) pwm_waarde <= pwm_waarde -1; // decrement begrenzen tot 0
      end
   end
end

// 8 bit pwm teller en pwm comparator output.
always @(posedge pwm_clk)
begin
  pwm_teller <= pwm_teller +1;
  if ((pwm_teller == 0) & (pwm_waarde > 0))max_led <= 0; // actief low, dus 0 sturen
  if (pwm_teller == pwm_waarde) max_led <= 1;            // 1 sturen = afleggen
end
endmodule