20 Jun
2012
20 Jun
'12
10:01 p.m.
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.
No, it's not hard to work them out -- mostly. But if you are trying to
learn about the 68000, it helps if you don't have to do guesswork on the
way ;)-)
[...]
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.
I haev my own compelte scheamtics of the Mac+ (both boards, keyboard,
mouse, disk drive), but of course nothing definite on the PALs.
I have thoguth of a fully-documetned 68000 board. The Sage II. It's a
single board, sitting on top of disk drives and PSU. It's all standard
ICs (TTL and normal I/O devices), _all_ of which are in sockets. And
there's a schematic in the user manual. The onyl problem is finding such
a machine.
-tony
