[Coco] 8 slot multi pak

[RETRO Innovations]

The main problem with an extensive slot MPI (16 is the limit, at least 
without resorting to some trickery), is the way the MPI space has been 
abused in the past.

Glenside IDE (and thus all IDE controllers purporting to be compatible) 
abuse the SCS address space, which is gated in the MPI to ensure that 
only the currently selected slot gets the SCS signal.  Since the GIDE 
ignores the SCS line, it responds to all $ff5x addresses, regardless of 
slot selection.

That means only $ff4x is alone available for slots to guarantee a free space

$ff6x and $ff7x are there as well, they are global, so the MPI treats 
those locations like a big Y cable for all signals except for ROMs.

In other words, for slot values >4, each one deliver less additional value.

I think the better approach is for Darren to expand his CocoFDC to 
include a bit of uc/CPLD code to emulate an IDE port, add a cc90, and 
maybe add a few more items that folks feel are absolutely necessary.  
Then, pop that in a regular MPI with specialized cart like Zippster's 
PSG cart, or similar, and enjoy.

Jim