Got an interesting one here... I'm trying to use UART0 on a 644A to talk to a u-blox6 GPS chip, and failing.
The same code, same pins, same voltage, same clock speed, same everything, works fine on the 324P.
Carrying the physical gps chip between the two boards shows me it works in the 324 but not the 644.
The point is... poking around with a USB serial probe shows the *exact same data* being delivered to the pin on the ublox, but it just doesn't give a response as expected. There *is* data, but it's the default NMEA codes which I don't want. The gps chip ignores the mode change message and also ignores commands to change the NMEA messages.
/me is completely confused... is there some really subtle difference between the two UART0s?