"251 is still an 8-bit controller since it has an 8-bit data bus"

I believe the bitwidth of a controller is defined by the width of the ALU and the INTERNAL data bus, by that definition the 251 is a 16 bitter.

If the EXTERNAL data bus is the defining factor, what does that make the XA, It can be configured with an external data bus 8 or 16 bits wide, but the Internal RAM and flash will still be accessed on a 16 bit bus.

Erik