1.2.4 Address Match Unit

The Address Match unit is only used in slave mode, and checks if the received address bytes match the 7-bit address in the TWI Address Register (TWAR). Upon an address match, the Control Unit is informed, allowing correct action to be taken. The TWI may or may not acknowledge its address, depending on settings in the TWCR.

On devices with a TWI Address Mask Register (TWAMR) the Address Match unit can react on a masked subset of addresses.

Although the clock system to the TWI is turned off in all sleep modes, the interface can still acknowledge its own Slave address or the general call address by using the TWI Bus clock as a clock source. The part will then wake up from sleep and the TWI will hold the SCL clock low during the wake up and until the TWINT Flag is cleared.