Problem with sending DMX

Question

I want to send DMX with my Arduino Mega 2560. I'm using the IDE 1.6.7

I tried the AVR -> DMX source code from Ulrich Radig and also the layout for the RS-485 transmission.

I modified the code to fit the ATMega2560 but when I upload the code nothing happens.

The only thing I didn't do is to use the 22 Ohm resistors, is that a problem?

Any idea?

Here is my circuit:

Here is the source

#include <avr/interrupt.h>
#include <avr/io.h>
#include <stdio.h>

#define F_CPU 16000000
#include <util/delay.h>

#define DMX_BAUD 250000
#define DMX_BAUD_BREAK 80000
#define DMX_BAUD_BREAK_UBBR ((F_CPU+DMX_BAUD_BREAK*8)/(DMX_BAUD_BREAK*16)-1)
#define DMX_BAUD_UBBR ((F_CPU+DMX_BAUD*8)/(DMX_BAUD*16)-1)


volatile unsigned char dmx_buffer[512];


//############################################################################
//DMX Senderoutine
ISR (USART_TX_vect)
//############################################################################
{
  static unsigned int  dmx_channel_tx_count = 0;
  static unsigned char dmx_tx_state = 0;

  switch (dmx_tx_state)
  {
    case (0):
      UBRR0   = DMX_BAUD_BREAK_UBBR;
      UDR0 = 0; //RESET Frame
      dmx_tx_state = 1;
      break;

    case (1):
      UBRR0   = DMX_BAUD_UBBR;
      UDR0 = 0; //Start Byte
      dmx_tx_state = 2;
      break;

    case (2):
      _delay_us(10);
      //Ausgabe des Zeichens
      UDR0 = dmx_buffer[dmx_channel_tx_count];
      dmx_channel_tx_count++;

      if(dmx_channel_tx_count == 512)
      {
        dmx_channel_tx_count = 0;
        dmx_tx_state = 0;
      }
      break;
  }
}

void setup() {
 //Init usart DMX-BUS
 UBRR0   = DMX_BAUD_UBBR;
  DDRE |= (1<<PE1); //Output TXD Pin ATmega2560
  UCSR0B|=(1<<TXEN0)|(1<<TXCIE0); // TXEN0 Transmitter enable / TXCIE0 TX complete interrupt enable
  UCSR0C|=(1<<USBS0); //USBS0 2 Stop bits
  sei();//Globale Interrupts Enable
  UDR0 = 0;//Start DMX

}

void loop() {
  // put your main code here, to run repeatedly:
    dmx_buffer[4]=255;
    _delay_ms(1000);
    dmx_buffer[5]=255;
     _delay_ms(1000);
    dmx_buffer[6]=255;
    _delay_ms(1000);
    dmx_buffer[4]=0;
    _delay_ms(1000);
    dmx_buffer[5]=0;
     _delay_ms(1000);
    dmx_buffer[6]=0;
     _delay_ms(1000);

}

Answer 1

The only thing I didnt do is to use the 22 Ohm resitors, is that a problem?

Yes, that's a huge problem. The resistors are there to prevent reflections from distorting the signal. Without them the best you can hope for is a garbled mess.