hi all!
i'm playing around the software appleI monitor and i just realized that it's too simple the video software part.
so i take a fast look to the schematic found on the operational manual, but i think that some is missing.

in the applefritter.com site, i found few references about shift-regiters, char generator (and so on ic's) that maybe are connected to the 6820.

can someone give me a bit more info about that?

btw: the replica I resolved this problem with actual ic's

tnx!

As I recall, the video ram cannot be directly accessed. As you write to video port, the characters scroll across the screen on the bottom row. As more characters are received, the characters are shifted up in the RAM and on the screen. You cannot address them directly. This is kind of like a teletype device, with the history being scrolled up as new characters are received.

Someone can correct me ,as I may be wrong.

Daryl

You are right. In fact, the Apple 1 is a very simple 6502 computer with ROM (256 bytes!), RAM and all I/O via a 6820 PIA. Input is via a parallel keyboard, output characters are written to the 6820 parallel output. The other part of the Apple 1 is a video terminal attached tot hat 6820 port. That is where the shift registers, character ROM (2513) and such are used for.
The Apple 1 Replica and the A-ONE replace the RAM in the 6502 computer with a large SRAM. Also for the parallel keyboard input via a modern controller, a PS/2 keybaord can be used. But for the rest it is nearly identical yto the original, the 820 is still there.
The video terminal part is constructed with modern ATMEGA controllers, since the IC's in the Apple 1 are very rare.

More on the Apple 1 and Replica's on Vince Briel's, San Bergmans and my site.

Hans, http://retro.hansotten.nl

yes, ok, but isn't there the original appleI "terminal" i/o schematic?
i cant believe it's gone lost!

i really dont care too much about it, but i find it interesting..

tnx

ps:
not so much time to work on sbc2 monitor, maybe in the weekend

The Apple 1 Operations Manual has the full schematics.

Here's a link to download it:

http://www.applefritter.com/filestore2/ ... /a1man.pdf

Daryl

sorry, i know this manual, but i exchanged the first page circuit with a normal ram bank (printing 2 pages in 1 sheet maybe it's a bit confusing...)

thank you