Probleme ATmega164P + PCA9554

[Luky S. (luky)]

Ich habe eine simple Testroutine zum Ansteuern eines externen I2C 
Treiberbausteines erstellt. Leider reagiert der Baustein überhaupt nicht 
auf die Ansteuerung...
Ich habe die Kommunikation auf dem Bus mal aufgezeichnet und angehängt.

#define ADDRESS 0x20

void Init_TWI (void)
{
  TWBR = 72; //set Bus speed 100kHz @16Mhz MCKL
}

void TWI_send_start (void)
{
  TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN); //Send START condition
  while (!(TWCR & (1<<TWINT))); //Wait for TWINT Flag set.
}

void TWI_send_add_rw (unsigned char address, unsigned char rw)
{
  unsigned char addr_byte = 0;

  addr_byte = address << 1; //shift address one bit left
  addr_byte |= rw; //set RW-Bit, if necessary

  TWDR = addr_byte;
  TWCR = (1<<TWINT) | (1<<TWEN); //send content of TWDR
    while (!(TWCR & (1<<TWINT))); //wait, until address has been sent
}

unsigned char TWI_read_byte (void)
{
  TWCR = (1<<TWINT) | (1<<TWEA) | (1<<TWEN);
    while (!(TWCR & (1<<TWINT))); //wait, until byte has been received
  return TWDR;
}

void TWI_send_byte (unsigned char byte)
{
  TWDR = byte;
  
  TWCR = (1<<TWINT) | (1<<TWEN); //send content of TWDR
    while (!(TWCR & (1<<TWINT))); //wait, until byte has been sent
}

void TWI_send_stop (void)
{
  TWCR = (1<<TWINT) | (1<<TWSTO) | (1<<TWEN);  
  delay_ms(1); //wait a bit
}

int main(void) {
  
  Init_TWI();
      
while (1) {
    

  TWI_send_start ();

  TWI_send_add_rw (ADDRESS, 0);

  TWI_send_byte (0x1);
  TWI_send_byte (0x0);
  TWI_send_stop ();
  USART_transmit(input);


  delay_ms(2000);
      
}  //while


} //main