TMP275: I2C read problem

Longchang Chen

Part Number: TMP275

Hi :

We have a question about the part TMP275, we found that the last bit of read is “ACK by Master”, we want to know whether there is any problem if our CPLD internal I2C read TMP275 with NACK but not ‘ACK’ before stop, Is this bit must be “ACK” for TMP275? You know some other sensor I2C part is “NACK” in their spec, Our CPLD also access other sensor parts. It’s urgent for us, Thanks.

over 6 years ago

0 Josh Wyatt over 6 years ago

TI__Guru* 91206 points

Dear Longchang -

Within an I2C transfer, after the side reading a byte (master on a receive or slave on a send) receives a byte, it must send an ACK.

The major exception is if the receiver is controlling the number of bytes sent, it must send a NACK after the last byte to be sent.

For example, on a slave-to-master transfer, the master must send a NACK just before sending a STOP condition to end the transfer. (This is required by the spec.)

It seems you are describing part of a normal condition - but please confirm that depending on the situation, an ACK or NACK is sent by Master.

See and follow page 10, here in this case: https://www.nxp.com/docs/en/user-guide/UM10204.pdf