Hi ZJY, We limit the fsystem (MCLK) as 25MHz in the datasheet: Also limit the I2C clock the same as MCLK: The limitiation comes from the microcontroller design. And we do not guarantee the spec out of the range. [quote userid="574265" url="~/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/1502258/msp430f5529-use-i2c-module-to-read-data---after-set-mclk-as-32mhz/5774421#5774421"]I want to make sure why this happened. Is there any thing wrong with my main code, or may because of the high MCLK? [/quote] What I suspect is that, the NAK reply from salve is late than you process the NAK check. If you are working with following data transfer, the TXBUF will be discarded where there is a NAK occurs. While if you are working with next re-start signal, there looks like no hardware mechanism to discard it. So, I suggest you add some dealy before next re-start signal and see whether it could work. B.R. Sal
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