When the TWI is configured as a client, it will wait for a Start condition to be detected. When this happens, the successive address packet will be received and checked by the address match logic. The client will ACK a correct address and store the address in the Client Data (TWIn.SDATA) register. If the received address is not a match, the client will not acknowledge or store the address, but wait for a new Start condition.
The Address or Stop Interrupt Flag (APIF)
in the Client Status (TWIn.SSTATUS) register is set to ‘1’ when a Start
condition is succeeded by one of the following:
- A valid address match with the address stored in the Address (ADDR[7:1]) bit field in the Client Address (TWIn.SADDR) register
- The General Call Address (0x00), and
the Address (ADDR[0]) bit in the Client Address (TWIn.SADDR) register is set to
‘
1’ - A valid address match with the
secondary address stored in the Address Mask (ADDRMASK) bit field, and the Address
Mask Enable (ADDREN) bit is set to ‘
1’ in the Client Address Mask (TWIn.SADDRMASK) register - Any address if the Address
Recognition Mode (PMEN) bit in the Client Control A (TWIn.SCTRLA) register is set to
‘
1’
A Start condition immediately followed by a Stop condition is an illegal operation, and the Bus Error (BUSERR) flag in the Client Status (TWIn.SSTATUS) register is set.
Depending on the Read/Write Direction (DIR) bit in the Client Status (TWIn.SSTATUS) register and the bus condition, one of four distinct cases (S1 to S4) arises after the reception of the address packet.
