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TMP275: ACK or NACK at the end of the transfer

Kai Nomiyama
Expert 5285 points
Part Number: TMP275

Hi Team,

I have a question about TMP275 I2C communication.

TMP275 datasheet figure 9 shows Two-Wire Timing Diagram for Read word format.
When we see end of transfer(byte2 bit9), that SDA is ACK.
However, when we see NXP I2C bus specification, there is comment that "5.A master-receiver must signal the end of the transfer to the slave transmitter.".

Question here is should we send NACK at byte 2/ bit9 or send ACK as datasheet figure 9?

refer to https://www.nxp.com/docs/en/user-guide/UM10204.pdf

Regards,
Kai

  • 0
    TI__Expert 8970 points

    Hi Kai,

    Thank you for posting.

    Figure 9 of the TMP275 datasheet shows a stop condition at the end of the transfer. To signal a stop condition, the SDA line transitions from low to high while the SCL line remains high. This agrees with section 3.1.6 of the NXP I2C bus specification that requires a signal at the end of the transfer.

     

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    TI__Expert 5285 points

    Hi Nicole,

    In general, once the master has received the number of bytes it is expecting, it will send a NACK, signaling to the slave to halt communications and release the bus.
    The master will follow this up with a STOP condition like below figure.
    However, it looks TMP275 figure 9 shows not NACK but ACK at the end of transfer with STOP condition.

    refer to https://www.ti.com/lit/an/slva704/slva704.pdf

    Again, the question here is do we send ACK or NACK at the end of transfer that means frame5/ byte2/ bit9?

    Regards,
    Kai

  • 0 in reply to Kai Nomiyama
    TI__Expert 8970 points

    Hi Kai,

    I apologize if I misunderstood your initial question. You are correct that a NACK should be sent at the end of the transfer. In Figure 9 it should be a NACK shown at the end of the read. I will make sure this correction appears in the next datasheet update.

     

    Best regards,

    Nicole