Re: Hardware Project

[david@uow.edu.au (David Wilson)]

dcross1@nospam.home.com (David Cross) writes:
>If I understand what you're saying, you propose to replace three separate chips 
>(?) or groups of code with one chip, or more condensed code.

>My question is: Was there a reason why this wasn't practical or possible, say, 
>10 years ago when the Apple // series was a going concern?

Late vintage cards (eg Apple 1MB RAMCard (Slinky), HS SCSI etc) did use
custom logic chips to save on all the glue chips that a typical design
needs.

The early Apple // cards (Disk II, Parallel Printer card) used 256byte
ROMs which fitted perfectly into the CnXX space.

Later cards (Super Serial Card etc) used 2KB ROM with external logic to map
it into CnXX and C800..CEFF using the two selects IOSEL and IOSTB.

Still later a 4KB ROM was used with half the chip in C800..CFFF and the other
half used for the CnXX space - the code replicated 7 times - once for each slot.

Until relatively recently home made designs would not have used programmable
logic devices such as PAL/GAL or more complicated ones due to the cost of
the programmers (and the chips as well) - not that many people would have
even had an EPROM Programmer at home I would guess.

So my idea was to program a GAL to cut the number of glue chips down from
over five to about two (at least the chips that are common to any Apple //
card). The other suggestion made was to replace all of them with a single
PLD (44 pins or such like).
--
David Wilson  School of IT & CS, Uni of Wollongong, Australia  david@uow.edu.au