Subject: Re: Hardware Project
From: "Terence J. Boldt" <apple2@cgocable.net>
Date: Tue, Nov 17, 1998 6Ç46 
Message-id: <36517e53.0@news.cgocable.net>

>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.


I finally get it... :-)  I'm making a quick mod to my design (adding 3
address lines) to allow the 256 byte code to be non-relocatable.  I wrote
the ProDOS entry and card controlling routines in about 80 bytes, but to
make it relocatable, I had trouble squeezing it all in 256 bytes (still
didn't work).  I don't know why I didn't think of this on my own, but heck,
I'm always willing to accept ideas from intelligent/knowledgeable people.

>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.


GAL/PAL's would save at least two chips in my design, but I have an EPROM
programmer and not a PAL/GAL programmer.  The EPROM programmer and eraser I
ordered from the States a couple years ago cost me only $125 U.S. together.
At the time a PAL/GAL programmer was $300+.

>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).


This is definitely the way to go nowadays.  Maybe my next project will use
something like this, but for now I'll use obsolete equipment because I'm
saving for another motorcycle.  (No, we don't have snow 365 days a year in
Canada eh?)  :-P

-- Terence J. Boldt