# Receiving Data Packets

Assuming the M2 case above, the clock is released for one byte, allowing the client to put one byte of data on the bus. The host will receive one byte of data from the client, and the Read Interrupt Flag (RIF) will be set to ‘1’ together with the Clock Hold (CLKHOLD) flag. The action selected by the Acknowledge Action (ACKACT) bit in the Host Control B (TWIn.MCTRLB) register is automatically sent on the bus when a command is written to the Command (MCMD) bit field in the TWIn.MCTRLB register.

The software can prepare to take one of the following actions:
• Respond with an ACK by writing ‘0’ to the ACKACT bit in the TWIn.MCTRLB register and prepare to receive a new data packet
• Respond with a NACK by writing ‘1’ to the ACKACT bit and then transmit a new address packet
• Respond with a NACK by writing ‘1’ to the ACKACT bit and then complete the transaction by issuing a Stop condition in the MCMD bit field from the TWIn.MCTRLB register

A NACK response might not be successfully executed, as the arbitration can be lost during the transmission. If a collision is detected, the host loses the arbitration, the Arbitration Lost (ARBLOST) flag is set to ‘1’, and the bus state changes to Busy. The Host Write Interrupt Flag (WIF) is set if the arbitration was lost when sending a NACK or a bus error occurred during the procedure. An arbitration lost during the sending of the data packet is treated in the same way as the above M4 case.

The RIF, CLKHOLD, ARBLOST and WIF flags are all located in the Host Status (TWIn.MSTATUS) register.

Note: The RIF and WIF flags are mutually exclusive and cannot be set simultaneously.