replacing AT90S8515

Hi,
thanks Jason for your suggest, but the Micro still not works.
Only a rail to rail signal swing change on the XTAL2 signal, but I think
this is more correct because this is the same amplitude I found on the
AT90S.
But by comparing the XTAL2 signal between At90S and MEGA (on an evaluation
board with 4 MHz cristal) I see a frequency difference:
AT90S: XTAL2 freq ~ 860 KHz
MEGA:	XTAL2 freq ~ 560 KHz
why this happens? what can I set too? I change also SUT fuses to 11 (65 ms
additional delay) but, as I expected, nothing was changed.

Bye.

Alessandro Serafini