Hi Gil,

sounds, you are a pure software guy.

There is no way for any memory to vary the speed. You must read the EPROM data sheet to be sure, that it was fast enough for the micro.
You must always check the worst case conditions.
If it fits not, the only chance was to use another crystal.


Additional on the new DS89C420 different timings can be selected. But this must be done from the internal memory before any external access take place.


Peter