ahref:
Fantastic, Does anyone know the logic as to why the SPI pins were moved in the mega.I'm guessing it was the layout of the pins on the actual microcontroller combined with its size that made it hard to get them back to their old places ?
The statement on its product page about most UNO shields being compatible was misleading
Not only is the SPI signals on different pins for the Uno Vs mega boards, but also the I2C clock and data signals are on different pins. This does make shield compatibility a challenge for shield builders and is probably the reason that so many shields are Uno compatible only without wiring modification or jumper clip options built onto the shield. The new arduino ARM based board, the Due will make shield compatibility even more difficult in the future.
Lefty