The Naked Atari 800

[rubber_jonnie]

That is very helpful indeed, thanks for that, I had been finding it difficult to get the schematics for the board, makes a big difference when you can see what goes where :)

Note that it seems it's not same exact board you have. The schematics are for a NTSC Sally board. The actual PAL logic with the second crystal is missing.

As a matter of fact the schematics describes a Sally CPU board with CTIA, not with GTIA. Interesting, but I doubt such a board was ever shipped in that configuration. By the time that Sally was released, all boards probably shipped with GTIA, and not CTIA.

Definitely interesting, I'll have to have a proper read through it, but the PCB on page 18 looks very like a PAL cpu board thats missing the crystal etc.

[rubber_jonnie]

OK, so now I have 2 test rigs:

IMG20260123130411.jpg

Top one I built first and works with the Digispark SMD/USB board, but as I also have some DIL packaged ATTiny85's for similar USB boards, and I wanted a board where I could just pop out the IC and program it with the TL866 rather than all the hassle of desoldering the SMD device.

As it goes I am likely to wire up the programming pins on the SMD test rig, I just haven't got round to it yet.

And the whole thing works great, the ATTiny has no bootloader and just fires the config straight into the Si5351 on power up and then goes into idle, with a slow flashing LED to confirm the programming is done and that's it's now idling.

Pretty pleased with the results, I no longer have to worry about missing crystals as long as they are in the range 8Khz to 160Mhz :)

A minor bonus along the way, I thought I'd killed one of my SMD USB Digispark boards, turned out I hadn't, just somehow erased the bootloader :lol:

All programmed now and working just fine again.

[stephen_usher]

I guess that you could reduce the over all footprint size if necessary by putting the ATTiny85 under the clock board and using the system's own VCC to power it, meaning that you don't need the USB socket etc. Maybe even just bodge wire the ATTiny 85 on top and hot glue it.

[rubber_jonnie]

I guess that you could reduce the over all footprint size if necessary by putting the ATTiny85 under the clock board and using the system's own VCC to power it, meaning that you don't need the USB socket etc. Maybe even just bodge wire the ATTiny 85 on top and hot glue it.

Yeah, those are literally just test rigs for the ATTiny and clock boards - does the program do what it's supposed to, so there is a lot of scope to reduce the footprint overall, need to think about that next.

On the 800 it is currently running off VCC, the USB socket isn't in use at all. The two boards are just wired together so I'm going to have a look an see what can be done to reduce the size.

[rubber_jonnie]

@stephen_usher

This is the current lash up in the 800:

IMG20260123144023.jpg

So I need to figure out a nice small footprint for it for when I use it permanently.

[stephen_usher]

:dualthumbup:

[rubber_jonnie]

I was a little surprised to find this on eBay for a very reasonable price, just £10:

Screenshot 2026-01-24 at 12.02.54.png

And whilst it isn't in perfect condition, it should clean up pretty easily and it will give the 800 a bit of solidity that it doesn't have right now and should clean up very easily. I'll need to make a bottom plate for it but that should be relatively straightforwards.

As a further experiment with the clock generator this morning I decided to try and see if I could program all 3 clocks with the well known Atari frequencies:

1. 3.546894MHz PAL Master clock
2. 4.433618Mhz PAL Colourburst clock
3. 3.579575 Mhz NTSC Master clock

Now I know what I'm doing I can easily generate the register settings using Clockbuilder Pro and import them into the Arduino IDE script for the ATTiny85 then export that as a HEX file that can be used for programming the IC using a TL866.

I think I'm going to put together a repository on GitHub with details of how to do it all and what you need to do it, and I'll include some ready built hex files with common frequencies.

If I get time I'll also build a new module for the Atari 800 using one of these I have to hand:

Screenshot 2026-01-24 at 12.23.41.png

It has one less channel, but certainly in most Atari situations 2 channels is all that's needed and it is much smaller than the 3 channel devices and in fact a similar size to the ATTiny boards (Both SMD and DIL) so will make for a much neater solution. It also comes with Stemma QT 4 pin connectors which could ultimately mean a much neater set up.

More on that later if I get round to it.

[ijor]

Definitely interesting, I'll have to have a proper read through it, but the PCB on page 18 looks very like a PAL cpu board thats missing the crystal etc.

Yes, it seems the board layout itself is the same for PAL or NTSC. But not only that the PAL stuff is not populated in the picture, it is not included at all in the schematics either. That is, the schematics are for an NTSC, Sally based, CPU board. I assume the PAL logic is the same than the one included in the original 400/800 schematics. So if you take the Sally schematics from the Sam's book, and you add the PAL stuff from the original schematics, it should probably much your board.

[rubber_jonnie]

Definitely interesting, I'll have to have a proper read through it, but the PCB on page 18 looks very like a PAL cpu board thats missing the crystal etc.

Yes, it seems the board layout itself is the same for PAL or NTSC. But not only that the PAL stuff is not populated in the picture, it is not included at all in the schematics either. That is, the schematics are for an NTSC, Sally based, CPU board. I assume the PAL logic is the same than the one included in the original 400/800 schematics. So if you take the Sally schematics from the Sam's book, and you add the PAL stuff from the original schematics, it should probably much your board.

I expect so yes. I hadn't realised that some 800's had Sally CPUs, but it makes sense now as it wouldn't work with a known good 6502.

As it goes the CPU board is from a 400 and I don't recall it having a Sally, but I can't remember from when I upgraded the 400 to an SCCC last year. I think it must have been otherwise the PAL board wouldn't b working with a Sally in it!!

And yes, looking back at the pic from my Atari 400 thread it's definitely a Sally. I didn't realise 400's & 800's ever had Sally CPU's, you learn something new every day :)

[ijor]

I hadn't realised that some 800's had Sally CPUs, but it makes sense now as it wouldn't work with a known good 6502.
...
I didn't realise 400's & 800's ever had Sally CPU's, you learn something new every day :)

I learnt about that not too long ago. I also thought that Sally started with the 1200XL. May be also in the latest 400/800 units.

But what I found out these last couple of days, thanks to some research motivated by this thread, is that Sally appeared much earlier, and that it seems that actually ALL PAL CPU boards are Sally based!