I just spent the last two hours trying to figure out why all of the UART-related register code was failing on my 5529LP. After hooking up to a different 5529, where code performed as expected, I finally remembered that several months ago I'd found that one of my LP boards had a "broken" UART/I2C - Of course, I'd not marked the board when I set it aside. Dumb. Board is marked now. It's still useful for other experiments, so I'll keep it on hand; I just won't use it for any comms protocols.