The Address Match unit checks if received address bytes match the seven-bit address in the TWI Address Register (TWARn). If the TWI General Call Recognition Enable bit (TWARn.TWGCE) is written to '1', all incoming address bits will also be compared against the General Call address. Upon an address match, the Control Unit is informed, allowing the correct action to be taken. The TWI may or may not acknowledge its address, depending on settings in the TWI Control Register (TWCRn). The Address Match unit is able to compare addresses even when the AVR MCU is in sleep mode, enabling the MCU to wake up if addressed by a Master.