20 Jun
2012
20 Jun
'12
12:18 p.m.
On Jun 19, 2012, at 4:10 PM, Tony Duell wrote:
Most of the PALs in the original Mac weren't super-complex. The most
complex ones, as far as I can tell, are the DRAM controller and the
sound chip; the rest were just memory decoding. Of course, a PAL does
handle the somewhat complex 68000 bus logic, which I guess would be
the real magic behind a 68K board.
As for the address decoding PALs, they're fairly simple to guess
what the equations might be if you know the address map. I have
the hardcover Inside Macintosh 1/2/3 book, which has the address
maps for everything up through the SE, IIRC.
There is a somewhat reduced and difficult-to-read schematic of the
original Mac logic board at Andy Hertzfeld's folklore.org site:
http://folklore.org/projects/Macintosh/images/schematic.jpg
This was a one-page reduction used for service, so it's primarily
used for tracing out connections, but it looks fairly complete.
- Dave
An
"established system" (by which I think you mean "a commercial
packaged/closed system") just plain denies a person that option, unless
you go dig up the schematics for it.
And in that case, say for an Atari or an Amiga, there are so many
complex custom chips in there, a beginner isn't going to get much of an
education out of it.
AFAIk the Mac hardware was never rully documetned. There may be
reverse-engineered schematics of some older Macs, but they all have
either custom chips or copy-protected PALs, so you can't get very far... 