Don't forget that if you're considering doing a 28MHz CPU for the SAM, you may want to consult with me and /or Martin Rookyard regarding the fiddly details you'll have to worry about :)
We had a prototype that ran at 12MHz with an overclocked Z80... and discovered that you'd need to have some glue (probably a finite state machine) in the middle that marshals memory and IO transactions over to the internal memory. Or possibly not; the Z380 (which is what I presume you're thinking of using) has different wait-state logic, and can hang on a half-clock if you need it to, so it might not be an issue. Simple solution: Try it and see ;) Simon
