[sebhc] Re: Re-creating actual floppies from archive

Peter Shkabara peter59 at sbcglobal.net
Sat Apr 1 23:32:09 CST 2006

I might pipe in at this point. When I made the 4MHz and 6MHz mods for the
H89, I found that 4MHz was fine with a few IC changes, but I ran into great
difficulties at 6MHz. The solution ended up being a software patch to have
the operating system drop operation back down to 2MHz when I/O access was

Peter Shkabara
peter59 at sbcglobal.net

-----Original Message-----
It's been a long time, and I've forgotten the details. But I ran across it
when I was designing the H-1000 (a replacement CPU board for the H89). The
old 8250 had a bus fight problem with the Z80 at 4 MHz, and both new and old
8250 had problems at both 2 MHz and 4 MHz. National had an application note
that outlined the problem.

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