68K ISA project

[Eric Smith]

Chris M wrote:

>  please share. It's not nice when you don't share.

The schematic has been online for ten years:

http://www.brouhaha.com/~eric/retrocomputing/apple/apple2/68020/

If anyone were to actually build one, I could probably dig up the PAL 
equations.

 >> so I occasionally get tempted to build S/N 2.
 > not often enough apparently

Plenty often enough, but my TODO list is *extremely* long, and nearly 
everything else is more urgent.

 >> Originally I wanted to design an upgraded version that could
 >> DMA into the Apple memory, for higher performance graphics.
 > DMA oftentimes is simply a chip. So witch chip you wuz gonna use?

There isn't any off-the-shelf chip that can adapt a 68K to act as a bus 
master on an Apple II in any sensible manner.  I would have had to 
design my own logic for that.

 > Now this thing was some sort of coprocessor thing I guess, right?

Yes.

 > Could you be more specific. Details details.

There aren't really any more details to be had.  Sorry.  It was just a 
one-off hack.

Eric