Tony mentioned the need to run at 1Mhz. in another posting. That's a
hard requirement for proper functioning of a SoftCard style coprocessor.
It truly was a bit of a hardware hack. I have three or four SoftCards
and perhaps a half dozen AE Z80+ cards. Some will work in some systems.
None of them will work in all of my systems. One more reason to keep on
the lookout for an Applicard if you're serious about Apple CP/M. Never
found a box that an Applicard wouldn't work in and it coexists with any
and all accelerators on both IIe and IIgs - at high speed settings, too.
All the "Softcard-derived" Z80 cards used a syncopated 3.5MHz clock,
which was regarded even at the time as a major hack. Like some other
cards, it has tight bus timing margins, and so running it on a system
other than one it was tested in during design is actually running a
reliability test. ;-)