>
>We eventually found the problem - the 4414 has 256 bytes eeprom, so it has 
>no EEADRH register, and therefore no code to initialise it. The 8515 has 
>512 bytes, but EEADRH is initialised to 0 on reset, so no problem- no code 
>change needed.  However on the Mega8515, this register is not initialised 
>and powers up in a random state. This was not highlighted in the 
>'differences' section of the datasheet.

This is why I try never to depend on a power up state.
I init everything, unless I am forced, by space requirements, to remove 
that code.
I've done that for Zilog, 8051 variants, PIC, and Atmel.

Also, you'll hit another issue on early AVR parts, where X wasn't 
implemented as a 16 bit register. You CAN still use it as two 8 bit 
registers, but code written for the early parts will assume that XL will 
never increment XH, which is no longer true, or they will use XL as a 
pointer and XH to store other data, with somewhat bizarre results.

Still, pretty minor when jumping 8-10 years in processors.



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