Electronic – How many bytes can be sent in a single i2c message

This question has been solved in Ti website and the following is the solution which he added:

From looking at the USCI Operation, I2C mode section in the MSP430x2xx >Family User's Guide SLAU144I I think the UCTXSTT bit will be cleared after >the slave has ACKed its receive address, and before the data has been read >from the slave. Therefore, the following in the Receive function could read >the UCB0RXBUF before the data has been received:

  while (UCB0CTL1 & UCTXSTT); // Start condition sent? RXBuffer full?
  receivedByte = UCB0RXBUF;

Try changing to:

 while((IFG2 & UCB0RXIFG) == 0); // Wait until data read

 receivedByte = UCB0RXBUF;

Chester Gillon's post

I fixed my problem by changing some parts in the Receive function. Thanks >to Chester Gillon's post, it made me realise that STT interrupt occurs >right after the slave ACK the master. After checking the user guide >carefully, i found this:

If a master wants to receive a single byte only, the UCTXSTP bit must be >set while the byte is being received. For this case, the UCTXSTT may be polled to determine when it is >cleared:

So this STOP condition must occur after the ACK but before the second data >ACK. So i changed my receive function into this and it solved all my >problems:

uint8_t Receive(char registerAddr){
uint8_t receivedByte = 0;
while (UCB0CTL1 & UCTXSTP); // Ensure stop condition got sent
UCB0CTL1 |= UCTR + UCTXSTT; // I2C start condition with UCTR flag for >     transmit
while((IFG2 & UCB0TXIFG) == 0); //UCB0TXIFG is set immidiately
UCB0TXBUF = registerAddr; //write registerAddr in TX buffer
while((IFG2 & UCB0TXIFG) == 0); // wait until TX buffer is empty and >     transmitted
UCB0CTL1 &= ~UCTR ; // Clear I2C TX flag for receive
UCB0CTL1 |= UCTXSTT; // I2C start condition with NACK for single byte >     reading
while (UCB0CTL1 & UCTXSTT); // Start condition sent? RXBuffer full?
UCB0CTL1 |= UCTXSTP;
while((IFG2 & UCB0RXIFG) == 0); // wait until TX buffer is empty and >     transmitted
receivedByte = UCB0RXBUF; // I2C stop condition
return receivedByte;
}

Barışcan Kayaoğlu's post

https://e2e.ti.com/support/microcontrollers/msp430/f/166/t/265825

I've run into this problem myself recently. The error originates from the manufacturer's datasheet. When the 'negative' flag is set the proper computation is:

temp -= 256;  // correct!

instead of

temp = 256 - temp;  // incorrect! But this is the example in the datasheet!

Here are a couple examples of control code for the MCP9808 on Github:

lexruee/mcp9808

adafruit/Adafruit_MCP9808_Library