I am trying implement a PMBus master on MSP430 chip to command UCD3138 for LLC converter that has a TI default code on it.
It is working well when UCD3138 executes ROM, but I am getting almost random NACK on read commands when it executes through Flash. The success rate is below 50% and NACK happens almost in every other massage. I am running 250KHz CLK and tried to reduce it also up to 100kHz. The strange thing is NACK seems not to happen anymore when I ignore reading last byte of DATA, and I am still reading correct PEC after STP.
I would appreciate if anyone could help me out with this, I am not sure if it is a CLK timing problem or the order of reading data from ISR. I am reading one byte at each ISR after Restart, and last byte is read after STP is set.
Thanks,