void i2c_init(u08 address)
{
    i2c_Address = address;

    PORT_USI |= (1<<PORT_USI_SCL);                    // Set SCL high
    PORT_USI |= (1<<PORT_USI_SDA);                    // Set SDA high
    DDR_USI |= (1<<PORT_USI_SCL);                    // Set SCL as output
    DDR_USI &= ~(1<<PORT_USI_SDA);                    // Set SDA as input
    USICR =    (1<<USISIE)|(0<<USIOIE)|                // Enable Start Condition Interrupt. Disable Overflow Interrupt.
            (1<<USIWM1)|(0<<USIWM0)|                // Set USI in Two-wire mode. No USI Counter overflow prior
                                                    // to first Start Condition (potentail failure)
            (1<<USICS1)|(0<<USICS0)|(0<<USICLK)|    // Shift Register Clock Source = External, positive edge
            (0<<USITC);
    USISR    = 0xF0;                                // Clear all flags and reset overflow counter
}

        if( USI_TWI_statusReg.dataInRxBuf )
        {
              PORTB |= (1 << LED);
                 ........

void ReadSensor()    
{
    I2c_StartWait(SENSOR_ADDR | W);         // slave address, write to sensor
    I2c_Write(TWI_CMD_MASTER_READ);  
  
    I2c_RepStart(SENSOR_ADDR | R);   // slave address + read bit, read sensor
          
    Value = (unsigned long)I2c_Read(I2C_ACK) << 24;
    Value |= (unsigned long)I2c_Read(I2C_ACK) << 16;
    Value |= (unsigned long)I2c_Read(I2C_ACK) << 8;
    Value |= (unsigned long)I2c_Read(I2C_NACK) << 0;
  
    I2c_Stop();
}

(( USIDR>>1 ) == TWI_slaveAddress

#define SENSOR_ADDR  0x10

    I2c_StartWait(SENSOR_ADDR | W);         // slave address, write to sensor
    I2c_Write(TWI_CMD_MASTER_READ);  
  
    I2c_RepStart(SENSOR_ADDR | R);   // slave address + read bit, read sensor

TWI_slaveAddress = 0x08;
............
    case USI_SLAVE_CHECK_ADDRESS:
      if ( ( USIDR == 0 ) || ( ( USIDR >> 1 ) == slaveAddress) )
      {
          if ( USIDR & 0x01 )
        {
          overflowState = USI_SLAVE_SEND_DATA;
        }
        else
        {
          overflowState = USI_SLAVE_REQUEST_DATA;
        }
        SET_USI_TO_SEND_ACK( );
      }
.......

unsigned char send_byte(unsigned char val)
{
   USIDR = val;
   USISR = (1<<USIOIF);
   do
   {
      USICR = (1<<USIWM0) | (1<<USICS1) | (1<<USICLK) | (1<<USITC);
   }
   while ((USISR & (1<<USIOIF)) == 0);
  
   return USIDR;
}

void main()
{
    SETBIT(DDRB, USCK);
    SETBIT(PORTB, USCK);
    
    SETBIT(DDRB, DO);
    CLRBIT(PORTB, DO);
    
    CLRBIT(DDRB, DI);
    SETBIT(PORTB, DI);
        
    for(;;)
    {    
        SendByte(0x11);
        
        delay_ms(100);
    }
}

    // select clock phase negative-going in middle of data
    SPCR |= (1 << CPOL0);
        
        // data is sampled on the trailing (last) edge of SCK. SPI Mode - 3
        SPCR |= (1 << CPHA0);
        
    // Data order MSB first
    SPCR &= ~(1 << DORD0);
        
    // enable SPI
    SPCR |= (1 << SPE0);
    
    // clear status
    SPSR = SPSR;
    SpiTransferComplete = true;

    // enable SPI interrupt
    #ifdef SPI_USEINT
    SPCR |= (1 << SPIE0);
    #endif
}

void SendByte(unsigned char Data)
{
    unsigned char BitCount = 8;

    do
    {
        // Send bit to Slave, MSB first
        if(Data & 0x80)
        {
            SETBIT(PORTB, DO);
        }
        else
        {
            CLRBIT(PORTB, DO);
        }
        
        // Toggle SCK pin to send current bit
        CLRBIT(PORTB, USCK);
        SETBIT(PORTB, USCK);        
                
        // Get next bit to send
        Data <<= 1;      
    }
    while(--BitCount);

}