AVRFreaks.net

#include <avr/interrupt.h>
#include <util/twi.h>



volatile unsigned char receiver[12];
volatile unsigned char transmitter[12];
volatile unsigned char cmd_Index;
volatile unsigned char debug;



ISR (TWI_vect)
{
  unsigned char I2C_control = 0;

  I2C_control = TWSR & 0xf8; // Mask prescaler bits.
  switch (I2C_control)
    {
    case TW_SR_SLA_ACK: // Slave address with receive.
    case TW_SR_ARB_LOST_SLA_ACK:
      debug |= 0x40;
      cmd_Index = 1;
      break;
    case TW_SR_DATA_ACK: // Data received.
      debug |= 0x20;
      receiver[cmd_Index] = TWDR;
      cmd_Index++;
      break;
    case TW_SR_DATA_NACK:
      debug |= 0x10;
      break;
    case TW_SR_STOP: // Stop or repeated start received.
    case TW_ST_SLA_ACK: // Slave address plus transmit received.
    case TW_ST_ARB_LOST_SLA_ACK:
      debug |= 0x08;
      cmd_Index = 1;
      TWDR = transmitter[cmd_Index];
      break;
    case TW_ST_DATA_ACK:
      debug |= 0x04;
      cmd_Index++;
      TWDR = transmitter[cmd_Index];
      break;
    case TW_ST_DATA_NACK:
      debug |= 0x02;
      break;
    case TW_ST_LAST_DATA:
      debug |= 0x01;
      break;
    case TW_NO_INFO:
      PORTB |= _BV(PB6);  //Set red LED.
      break;
    case TW_BUS_ERROR:
      PORTB |= _BV(PB6);  //Set red LED.
      TWCR = _BV(TWINT) | _BV(TWSTO);
      break;
    default:
      PORTB |= _BV(PB6);  //Set red LED.
      break;


    }

  TWCR = _BV(TWINT) | _BV(TWEA) | _BV(TWEN) | _BV(TWIE);


}