The Slave Address register in combination with the Slave Address Mask register (TWIn.SADDRMASK) is used by the slave address match logic to determine if a master TWI device has addressed the TWI slave. The Slave Address Interrupt Flag (APIF) is set to ‘1’ if the received address is recognized. The slave address match logic supports recognition of 7- and 10-bits addresses, and general call address.

When using 7-bit or 10-bit Address Recognition mode, the upper seven bits of the Address register (ADDR[7:1]) represent the slave address and the Least Significant bit (ADDR[0]) is used for general call address recognition. Writing the ADDR[0] bit to ‘1’, in this case, enables the general call address recognition logic. The TWI slave address match logic only supports recognition of the first byte of a 10-bit address (i.e., by setting ADDRA[7:1] = “0b11110aa” where “aa” represents bit 9 and 8, or the slave address). The second 10-bit address byte must be handled by software.