Two last clues(?) identified, one of them noted previously but documented here with confirmations and one new observation supporting my theory statement.
Quote, GttMFH2e p.412___________________________________________________________
Pseudo-slot video in the Macintosh IIci
Like the built-in video in the Macintosh SE/30, the video interface in the Macintosh IIci simulates some features of a Macintosh II Video Card in a NuBus expansion slot. By simulating the features of an expansion card in a slot, the Macintosh IIci can share common System ROM with the other Macintosh models that use the MC68030 processor. This simulation of a video card in a NuBus slot is called
pseudo-slot video.
The video screen buffer in the Macintosh IIci occupies memory starting at $0000_0000 in physical address space. Using the memory management unit in the MC68030, the Macintosh IIci maps the screen buffer to logical address space starting at $FB000_0000. That address space was chosen because it is the same as the address space used by expansion slot $B in the six-slot in the six-slot models of the Macintosh II family.
________________________________________________________________________________
That $B was an intentional choice in the IIci design jibes with the above tidbit about operations of the PowerCache Accelerators and my guess that they step all over Interrupt/Slot/Pseudo-Slot assignments of the IIsi and SE/30.
Driving the video subsystems of either appears to me to require some kind of logical intervention to sidestep Slot Manager operations as well as the memory mapping issue techknight had previously noted.
The second discovery would be the existence of two versions of the Twin-Slot Adapter for the IIsi.
Rev1(?)
http://www.applefritter.com/node/20222
Rev2(?) (c)1992
http://www.applefritter.com/node/20222
Hopefully the differences between the two versions will shed some light on the Cloning Project requirements for someone competent. My guess is that later (read faster better, more likely to wind up in an SE/30) PowerCache Cards had on-board ROM and circuitry mods circumventing the need for the drastic interventions necessary for compatibility with previous models.
I'll also guess that the location of the last remaining IC and pin assignments of U1 on the simplified Rev.2 adapter will be crucial in reverse engineering.
WAG: the unimplemented pads at U3 on the Rev.2 adapter suggest to me the possibility that a Rev.1.5 version was produced with backward compatibility with earlier PowerCache models, possibly another crucial tidbit?
Dunno, I think I've done about all that I can at this point. I don't have any of the adapters linked here and I've never even seen the SE/30 adapter which puts me at a severe disadvantage. Pics would be greatly appreciated, posting them in the NuBus Mafia project on 'fritter would seem to be the most useful for later iterations of the cloning project.
I'll get the lead out and post pics there of the LCIII adapter myself, or have someone competent post them for me!
