ELV USB-I2C & Schrittmotorsteuerung iSMT

//TWI interrupt handler

//Handles all states of the TWI of the AVR that can occur in master mode

SIGNAL(SIG_2WIRE_SERIAL)

{

  if(TWSR==0x08 || TWSR==0x10)  //Start condition or repeated start condition transmitted by us => we are becoming bus master!

  {

    TWDR=TWIMasterSendBuffer[0];   //Load the address byte ("SLA+W" or "SLA+R")

    TWCR=0x85;                     //Generate start condition and send the address byte

    TWIMasterSendPtr=1;

  }

  else if(TWSR==0x18 || TWSR==0x20)  //Address byte ("SLA+W") has been transmitted => send our first data byte.

  {

    TWDR=TWIMasterSendBuffer[TWIMasterSendPtr++];

    TWCR=0x85;

  }

  else if(TWSR==0x28 || TWSR==0x30)  //We can send all the other data bytes.

  {

    if(TWIMasterSendPtr<TWIMasterSendCount)     //more data bytes to be sent

    {

      TWDR=TWIMasterSendBuffer[TWIMasterSendPtr++];

      TWCR=0xC5;   //send next data byte

    }

    else

    {

      TWCR=0xD5;   //No more data bytes to be sent => Generate stop condition to release the bus

      TWIInUse=FALSE;

    }

  }

  else if(TWSR==0x38) //Bus arbitration lost => release bus immediately

  {

    TWIErrorFlag=TRUE;

    TWIInUse=FALSE;

    TWCR=0xC5;

  }

  else if(TWSR==0x40)  //Address byte ("SLA+R") has been transmitted and ACK has been received => we can now start to receive data bytes

  {

    TWIMasterReceivePtr=0;

    TWCR=0xC5;  //request first data byte

  }

  else if(TWSR==0x48)  //Address byte ("SLA+R") has been transmitted and NOT ACK has been received => abort the read process

  {

    TWIErrorFlag=TRUE;

    TWCR=0xd5;  //generate stop condition and release the bus  0x95

    TWIInUse=FALSE;

  }

  else if(TWSR==0x50)  //a data byte has been read from the slave and acknowledged

  {

    TWIMasterReceiveBuffer[TWIMasterReceivePtr++]=TWDR;

    if(TWIMasterReceivePtr<TWIMasterReceiveCount)

      TWCR=0xC5;  //at least two more data bytes to get => send ACK

    else

      TWCR=0x85;  //only one more data byte to get => send NOT ACK

  }

  else if(TWSR==0x58)  //the last data byte has been read from the slave

  {

    TWIMasterReceiveBuffer[TWIMasterReceivePtr++]=TWDR;

    TWCR=0xD5;   //generate a stop condition and release the bus  0x95

    TWIInUse=FALSE;

  }

  else  //Unknown state, just reset the interrupt flag.

  {

    TWIErrorFlag=TRUE;

    TWIInUse=FALSE;

    TWCR = 0xC5;  //Acknowledge and reset the interrupt flag

  }

}