Ok. This seems to be a bit confusing :-)RS-485 could be either 2-wire half-duplex OR 4-wire full-duplex. I have not been implementing any RS-485 before (only RS232) but the information I found on the net is quite clear (have a look at http://www.bb-elec.com/tech_arti...basics.asp for example).
But the main question still remains: Could the built-in UARTs handle 256kbps?

Thanks for the suggestions regarding software implementation of UART but it would be nice finding a device with 2UARTs and CAN at a reasonable cost ;-)

Best regards

Patric