Re: Cassette port input frequency range? And CPU MHz ranges.

[mwillegal <mike@willegal.net>]

Take a look at the sync signal used on the stock Apple 1 and Apple II cassette interface on this page.  

http://www.willegal.net/appleii/aci.htm

Though the circuit works as a zero crossing detector, there are clear limits as to speed capability due to the relatively slow signal transition times on the comparitor side of the input capacitor.

You may get a bit more out of it, by using a digital music player which eliminates some the analog jitter involved with a real cassette player, but I'd be surprised if you could get 10x improvement.

Regards,
Mike Willegal