OddBudMan's DMX Receiver (GCC)

DMX receiving is a sinch.

Have a counter count the bytes as they come in at 250k. If you have an error (this is caused by a break in the dmx frame) reset your counter. Remember DMX spits out up to 512 channels at a time (+ start byte).

Here is some code I wrote in AVR-GCC.
This generates software PWM to dim LEDs from the input DMX signal.

CODE

#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/signal.h>

#define sei() __asm__ __volatile__ ("sei" ::)
#define cli() __asm__ __volatile__ ("cli" ::)
#define NOP() __asm__ __volatile__ ("nop" ::)
void wait(int);
void init_usart(void);

volatile int count,bytecount;
volatile int count,dmxcount,ch1,ch2,ch3,ch4,ch5,ch6;
volatile int i,j,k,ij;

SIGNAL (SIG_OVERFLOW0) /* Note [2] */
{
uint8_t temp=0x00;
if(count>=255)count=0; //8bit counter
if(count<ch1)temp|=0x01; //Channel 1
if(count<ch2)temp|=0x02; //Channel 2
if(count<ch3)temp|=0x04; //Channel 3
if(count<ch4)temp|=0x08; //Channel 4
if(count<ch5)temp|=0x10; //Channel 5
if(count<ch6)temp|=0x20; //Channel 6
count++;
PORTB=temp;
//PORTB=0x00;
}

SIGNAL (SIG_UART_RECV)
{
uint8_t status, data;
status=UCSRA;
data=UDR;

//Frame error | DOR error detects a break and resets dmx count
if(status&0x10){dmxcount=0;return;}
if(status&0x08){dmxcount=0;return;}

//check for start condition
if(dmxcount==0){
if(data==0){dmxcount++;return;}
}

// if(dmxcount==4)PORTB=~data;
if(dmxcount==1)ch1=data;
if(dmxcount==2)ch2=data;
if(dmxcount==3)ch3=data;
if(dmxcount==4)ch4=data;
if(dmxcount==5)ch5=data;
if(dmxcount==6)ch6=data;
dmxcount++;
}

void ioinit (void) /* Note [5] */
{
DDRB=0xff; //portb as output

/*Timer Interrput Settings
* prescaller at /256 */
TCCR0=0x01;
TIMSK|=0x01;
}

int main (void)
{
ioinit();
init_usart();
sei (); //turn on global interrupt
PORTB=0xff;
while(1){i=0;}
return 1;
}

void init_usart(void) {
//USART Control and Status Register A UCSRA - Not used in init

//USART Control and Status Register B UCSRB
/*
Bit 7 RXCIE: RX Complete Interrupt Enable 1
Bit 6 TXCIE: TX Complete Interrupt Enable 0
Bit 5 UDRIE: USART Data Register Empty Interrupt Enable 0
Bit 4 RXEN: Receiver Enable 1
Bit 3 TXEN: Transmitter Enable 1
Bit 2 UCSZ2: Character Size 0
Bit 1 RXB8: Receive Data Bit 8 0
Bit 0 TXB8: Transmit Data Bit 8 0
*/
UCSRB = 0x98;

/*USART Control and Status Register C UCSRC
Bit 7 URSEL: Register Select 1
Bit 6 UMSEL: USART Mode Select 0
Bit 5 0
Bit 4 UPM1:0: Parity Mode 0
Bit 3 USBS: Stop Bit Select 1 //2 stop bits
Bit 2 UCSZ1:0: Character Size 1
Bit 1 1
Bit 0 UCPOL: Clock Polarity 0
*/
UCSRC=0x8e;

/* 250kbps 8N2 */
UBRRH=0x00;
//UBRRL=1;
UBRRL=1;
}

DISCLAIMER: I wrote this code a little while ago now, so please be kind to my coding techniques shown in this sloppy example. I'm not even sure this will work straight off the bat but I think it should (as another poster mentioned things have changed of late with Start Byte codes, so this code is by no means 100% reliable - check the latest DMX spec revision [if you can find it...]). Hopefully this example can help others.

oddbudman