It looks suspiciously like you need 0x00 for off-chip and 0x0F for on-chip

The obvious thing to do is write a program to test the theory.

e.g. read-modify-write on-chip XRAM and off-chip XRAM

I have just read your data sheet, your on-chip is only 1024 bytes and I suspect that your off-chip is a lot larger. So you will soon see the answer.

The data sheet does look very clear, but I still think it is worth checking the real device. It is Atmel after all.


David.