> The Harvard architecture of PICs makes them
> less than ideal for a general purpose computer, however.  There may be
> variants of the PowerPC that can be assembled by hand.  I would look at
the
> various microprocessor families to see what might be suitable for a home
> built general purpose computer.

This is why I like the 8052 arch.  It's still a harvard arch (more or less)
but the newer "expanded" and "high speed" parts have allot of nice features.
AFAIK, all of the parts have the ability to combine the code and data
segments.  This lets you do all the "really fun" stuff that you can't
normally do on a harvard arch; like writing self modifying code. ;-)))
Another benefit is that you can start small and add more capability later
(such as external RAM and ROM up to 4Mb on Dallas 80c390).  The 8051/52
arch. is over 20 years old now and keeps on going like the Energizer bunny.
;-)  It has it's weaknesses of course, but then all platforms do.

As Olin says, there may be PPC, MIPS, 68K, Strong-Arm etc.... parts that you
could work with more easily than constructing an i86 based system from
scratch.

Some more reasons to lower your ambitions on a full fledged computer:

You can build 8052's up on breadboards and they will work fine.  A pentium
(or faster) is "never" going to run on a breadboard.  Interfacing to DRAM
memory is not fun, SRAM's are way easier to talk to.  The PC bus and chipset
is extremely complex, what with the ISA, PCI and AGP busses and their
associated bridges.  The test equipment needed to analyze and debug a PC bus
and memory interface would most probably not be available to you.  Once you
have everything connected correctly, you would need a physicist to help
explain why things didn't work as expected.

I'm not trying to "rain on your parade", but you may wish to first start
with a somewhat more "workable" set of hardware.  Regardless of what others
may think, it would *not* be a "waste of time" to attempt such a project.
The learning experience would be more than worthwhile.  And, I *can* see the
personal reward in accomplishing such a project, even if, in the end, it was
only able to display the traditional "hello world" on a display screen.  ;-)

If you still wish to proceed with your original idea, I wish you much luck
and fun.

michael brown

michael brown

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.