Re: Apple 1 replica is almost finished

["Vince Briel" <vbriel@comcast.net>]

I've got a few questions, though:

- Why are you using a an AT90S8515 rather than a ATmega8515? The latter
are pin compatible replacements, but can run at twice the speed while
costing 25% less [1]. Besides, Atmel is phasing out the AT90 line in
favour of the ATmega and ATtiny lines -- already, the 90S8515 is no
longer recommended for new designs.

The ps/2 keyboard adapter was a project I took on using the 8515 that came
with my STK500 programmer. I wanted to use the smaller ATMEGA8 like what is
used for the video, but my firmware uses timer interupt pin for the data
line on the keyboard and the atmega8 only has 1 full set of i/o. I haven't
used the atmega8515 but if its a drop in replacement, I'll do it. 8MHz is
more than enough for a keyboard encoder. Nobody can type that fast and the
firmware code is tight. But now the price is $2.50 cheaper than then
90S8515, and I was aware of the atmega8515 but I've been in a rush to finish
the final revision.

- Why are you using NTSC composite (or PAL? you don't say) rather than
VGA video?

Sorry, forgot to mention NTSC. I forgot to mention that at the site, I'll be
sure to update the page. Now, why not VGA? Good question. I usually get
people asking why I don't make it look just like the Apple 1. Well, I'm
trying to keep with most of the original format of the Apple 1. It's output
was NTSC composite video and it just doesn't feel right hooked up to VGA.
For just a standard singleboard computer, I probably would have gone that
way, but I at least want the authentic feel of the Apple 1. This is why
after adding the ps/2 keyboard adapter I decided to leave the option of an
ASCII keyboard. It really has the true feel of a classic early 8 bit
machine.

The ATmega should be fast enough for the latter, the image
quality of a VGA monitor is much better than that of a television or
composite monitor, and you'd be avoiding problems with different
television standards.

Yeah, I had a friend do the coding on the ATMEGA8 for the video. This was a
real sore spot as you probably know that interlaced TV signals are very
outdated and NTSC is worse to deal with than PAL. Maybe we can code a PAL
version later after the rollout depending on if there is enough demand. I
really don't know how many people will want one. This is the first and only
known Apple 1 replica to be created. Even though Woz handed out schematics
of his design as well as the monitor source, a lot of people just bought
from Apple.

- Can the �Cs be reprogrammed on the board, or do you have to remove
them?

I didn't make room for ISP, so yeah gotta remove it.

Finally, note that the link "The Circuit" on the web page is broken.

Yeah, I'm finishing up the revised version of the circuit. I should have
that up by this weekend.

Vince



[1] at least where I'm buying my components -- www.reichelt.de