Transmitting Data Packets

Assuming the M1 case above, the TWI host can start transmitting data by writing to the Host Data (TWIn.MDATA) register, which also clears the Write Interrupt Flag (WIF). The host continuously monitors the bus for collisions and errors during the data transfer. After completing the data packet transfer, the WIF flag will be set to ‘1’.

If the transmission is successful and the host receives an ACK bit from the client, the Received Acknowledge (RXACK) flag will be set to ‘0’, meaning that the client is ready to receive new data packets.

The software can prepare to take one of the following actions:

If the transmission is successful and the host receives a NACK bit from the client, the RXACK flag will be set to ‘1’, meaning that the client cannot or does not need to receive more data.

The software can prepare to take one of the following actions:

The RXACK status is valid only if the WIF flag is set to ‘1’ and the Arbitration Lost (ARBLOST) and Bus Error (BUSERR) flags are set to ‘0’.

The transmission can be unsuccessful if a collision is detected. Then, the host will lose the arbitration, the Arbitration Lost (ARBLOST) flag will be set to ‘1’, and the bus state changes to Busy. An arbitration lost during the data packet transfer is treated the same way as the above M4 case.

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