unsigned char i2c_start_wait(unsigned char address)
{
    uint8_t   twst;

   // send START condition
   TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);

   // wait until transmission completed
   while(!(TWCR & (1<<TWINT)));

   // check value of TWI Status Register. Mask prescaler bits.
   twst = TW_STATUS & 0xF8;
   if ( (twst != TW_START) && (twst != TW_REP_START)) return 1;

   // send device address
   TWDR = address;
   TWCR = (1<<TWINT) | (1<<TWEN);

   // wail until transmission completed and ACK/NACK has been received
   while(!(TWCR & (1<<TWINT)));

   // check value of TWI Status Register. Mask prescaler bits.
   twst = TW_STATUS & 0xF8;
   if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return 1;

   return 0;

}/*