Saw an interesting "feature" on a C8051F060 this week. I do not recall the details, but basically, if I enabled the SPI engine (as a slave) with the idle clock in one state, SPIBSY came true immediately and every byte received was shifted by one bit. Worked fine using idle clock in other sense. Luckily I could change the sense of the idle clock (and CLKPOL too, of course).
We learn as we go.
Bill
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