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Made Apple 1
Back around 1977, I ran across plans by Steve
Wozniak, AKA Woz, for the Apple 1 computer. I had the chips, and
the time, so why not? This is what I built. I no longer have the
set of plans I used, I have no idea what became of them. The
project took me about a month to complete, and though I
populated the board with chips and made sections of it run
perfectly, it didn't work well, and I soon abandoned the project. If I recall, I
suspected the problems were with the surplus dynamic RAMs, but
looking back on it, I also took some shortcuts in my
construction for lack of cash to do it right. For example, all
of the parts were used or surplus (even the IC sockets). I did
make an off board 1K static RAM board that worked better, but I had to
rob the chips from my Digital Group computer to populate it, and
I valued that computer far more. It was fun while it lasted.
The Circuit |
Homebrew Apple 1 Computer, circa
1977.
|
The Apple 1 was an ingenious design
that was very unique for the day. Based on the MOS Technology 6502, it
was probably the first hobby computer to ever be designed by a real
electronics engineer.
The Apple 1 used dynamic RAM, a far more economical memory than
static RAM, but very hard to use. Dynamic RAM required
"refreshing" every 2 ms. This was a heavy burden for an early
microprocessor, requiring special timing and controllers to stop or
pause the processor long enough to complete a refresh cycle 500 times a
second. Almost no one could make it work the first time! Miss a beat,
and you lose most or all your data. (I remember MITS had many problems
with their attempt, and although the Digital Group version worked fine,
a few modifications were required to the CPU and other boards to make it
work.)
Woz made it work. The Apple 1 used the same clock signal to refresh
the RAM, out clock the video and run the processor. It worked perfectly,
and made history. Mine didn't.
My home built version had several other differences from the Woz's
Apple 1, I already had a nice video card as part of my Digital Group
system, so I didn't build one on board. I also didn't have access to the
ROM listings, so I made a small boot ROM to load programs by keyboard.
That's all I can remember! |
