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]) represents the slave address and the Least Significant bit (ADDR[0]) is used for general call address recognition. Setting the ADDR[0] bit, 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.