megaavr0 TWI in Slave mode

void i2c_slave_init(uint8_t addr)
{
    PORTMUX.TWISPIROUTEA = PORTMUX_TWI0_ALT2_gc;    // Mux na PORTF 2 a 3
    // Inicicalizace z examplu
    TWI0.SADDR = addr|0x01;                         //Slave address & enable general call
    TWI0.SCTRLA = TWI_ENABLE_bm |                   //Enable slave peripheral
    TWI_APIEN_bm |                                  //Enable address match interrupt
    TWI_PIEN_bm |                                   //Enable stop interrupt
    TWI_DIEN_bm |                                   //Enable data interrupt
    TWI_SMEN_bm;                                    //Enable smart mode
}

// preruseni TWI Slave vector
ISR(TWI0_TWIS_vect)
{
    if(TWI0.SSTATUS & TWI_APIF_bm)                  //Address match/stop interrupt
    {
        // Pokud je kolize tak vynuluje priznak a potvrdi
        if (TWI0.SSTATUS & TWI_COLL_bm)
        {
            TWI0.SSTATUS |= TWI_COLL_bm;            //Clear Collision flag
            TWI0_SCTRLB = TWI_SCMD_COMPTRANS_gc;    //complete transaction
            return;
        }

        // Pokud je oslovena SLAVE adresa tak odpovi
        if(TWI0.SSTATUS & TWI_AP_bm)
            TWI0_SCTRLB = TWI_SCMD_RESPONSE_gc;     //Send ACK after address match
        else
            TWI0_SCTRLB = TWI_SCMD_COMPTRANS_gc;    //complete transaction after Stop
    }

    // Toto jsem presne nepochopil jak funguje
    // Potrebuju odvysilat 2 nebo 4 byty
    if(TWI0.SSTATUS & TWI_DIF_bm)                   //Data interrupt
    {
        if(TWI0.SSTATUS & TWI_DIR_bm)
        {
            TWI0.SDATA = data;                      //Transmit data for Master to read
            TWI0_SCTRLB = TWI_SCMD_RESPONSE_gc;
        }
        else
        {
            TWI0_SCTRLB = TWI_SCMD_RESPONSE_gc;
            data = TWI0.SDATA;                      //Receive data written by Master
        }
    }
}