jcallen@maxzilla.encore.com (Jerry Callen) (12/28/90)
>1). Just so you are aware, George and I have been discussing in broad strokes >the possibility of a 'universal' expansion board for the pc532. The basic >idea is a low cost CPU/EPROM/RAM board which one could add IO, etc. >(including with glue chips wiring to an XT adapter card edge connector). >At this point we have kinda come to an understanding that the concept >is worth exploring, but not much else. In any event PLEASE do not let >this hold you back from pursueing your project. This is pretty much what I had in mind for the floppy controller; I was hoping to produce something reusable for other expansion boards. In any case, it look like "better minds" are going to go after the universal expansion board, so I'll probably drop the DRAM and use SRAM. If the universal controller is ready before I have a working prototype, I'll switch over to that. I suspect my controller will be a one-of-kind widget... Having thrown in the towel, let me nonetheless offer some ideas for the universal expansion card. :-) I like the 32CG160; it's not all that expensive, you get two DMA channels, three timers and instruction set compatibility with the pc532 (so we all have the tools). At 16MHz you can get (best case) 4 megabytes/second using 8 bit DMA, which seems good enough to keep up with the pc532. The on-chip blitter would be handy for a low-cost video board. It has the improved "direct exception" mode of the 32532, so interrupt response is merely slow, not glacial. :-) It's easy to add one or two 74xx148s to get 15 interrupt levels. The wait state generator makes it really easy to attach slow peripherals (like the 8255). -- Jerry Callen jcallen@encore.com