I2C bus learning - check for deficiencies and fill gaps

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The IIC protocol stipulates that when the host is used as a receiving device, the host does not respond to the last byte to indicate the end of data transmission to the transmitting device (slave device). This is because each transmission should receive an acknowledgement signal before the next byte is transmitted. If the receiver responds at this time, it does not receive the last byte. If it is the last byte, the 9th clock cycle sends a non-acknowledgement signal (at this time, it sends either an acknowledgement signal or a non-acknowledgement signal), and finally sends a stop signal.

Not every 8-bit data transmission will have an ACK signal, with the following 3 exceptions:

When the slave cannot respond to the slave address (for example, it is busy with other things and cannot respond to the operation of the IIC bus, or there is no corresponding slave for this address), the SDA line is not pulled low in the 9th SCL cycle, that is, there is no ACK signal. At this time, the host sends a P signal to terminate the transmission or re-sends an S signal to start a new transmission.
If the slave receiver cannot receive more data during a transmission, it will not send an ACK signal, so that the master can realize this and send a P signal to terminate the transmission or resend an S signal to start a new transmission.
The master receiver will not send an ACK signal after receiving the last byte. Therefore, the slave transmitter releases the SDA line to allow the master to send a P signal to end the transmission.

Reference address：I2C bus learning - check for deficiencies and fill gaps - response signal ACK

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