Backplane Atari Computer

[ivop]

For now, I leave the 1090 slots of the board, but that's certainly something that could be added later at the left or right side. Depending on the amount of slots I need, the current board might be extended to 30.5 × 24.4 cm, which is ATX. But to keep the cost manageable, I'll stick to 20x20 for now. You can also daisy chain multiple boards by soldering pinheaders at the sides and use a flatcable.

 

Cards I will be making first are:

 

1. GTIA + basic composite video out

2. ANTIC

3. CPU

 

The test clocks and scope out the address and databus. After that,

 

4. MMU

5. PIA

 

Test this, with SysCheck for RAM and ROM

 

6. POKEY, stereo, plus audio mixer

7. ROM

8. RAM

 

Test, and finished

 

Then a SIO card with an SDrive, a SIO card with MIDI, and a SIO to normal SIO connecter converter.

 

Long way to go.

 

[danwinslow]

Looks great.

[ivop]

Thanks. Still considering whether I should put the MMU and PIA on a single card or not. Similar with RAM and ROM. Any opinions on that?

 

[+ZuluGula]

Is it going to be possible to install U1MB?

[ivop]

2 hours ago, ZuluGula said:

Is it going to be possible to install U1MB?

Sure, that should be possible. Either by connecting to the MMU and ROM card, or a dedicated carrier board could be created, and then remove the MMU card (or chip if it's on the same board as the PIA), and the ROM and extended RAM cards. It would need a 64kB base RAM card though.

 

[Mathy]

Hello guys

 

IIRC Candle is working on an external version of the U1MB.

 

Sincerely

 

Mathy

 

[ivop]

If the external U1MB will be a CART/ECI board, it should be plug and play after removing the MMU, RAM and ROM from the backplane. Hopefully it will also do the 64kB base RAM, otherwise it would still need a separate 64kB RAM card.

[ivop]

On 4/5/2021 at 7:27 PM, ivop said:

but I also did something extremely stupid. I overwrote my only copy of the bus proposal .ods file with an empty sheet

Turned out it was not a PEBKAC after all. I almost ran out of space on my home filesystem. Luckily I noticed because KiCad mentioned I was low on diskspace. Just for fun I tried LibreOffice Calc again. Saved a sheet. Added some values, saved again, and lo and behold, corruption! Unrecoverable by "repair" or whatever they call it. A proper program never overwrites the original. It writes a new file, and only if that was succesfull, it moves it to the old file. Or even better, renames the old file to .bak, and renames the old file to the new file.

 

Anyway, I moved 12GB to another partition, and it's all fine now. Recreated the bus design in Calc. Now moving on to the power supply part of the backplane.

Edited April 7, 2021 by ivop

[ivop]

Full Card prototype

 

 

 

 

This is 10x20 max (lines are 7.5 or 5 by 10cm). None of the cards will be this big. Most will only need CART/ECI and perhaps MISC.

 

 

[+mytek]

Cool concept ?

[ivop]

Added some LEDs for +12V and +5V:

 

 

You know, otherwise you are bound to plug in or unplug a card with the board still powered

 

I'm fairly sure this is the board I'm going to order soon. Any last minute comments?

 

It's 20x20cm. 5 boards would set me back $79 + shipping ($20+) + tax ($20+) + custom duties  (~$15), which is somewhere between $130-$150 probably. That's for a four layer 2.0mm board, 2oz front and back copper, and 1oz sandwiched copper for the inner layers. Oldskool 4lyr 1.6mm 1oz/0.5z is on $13 cheaper, so a sturdy board it is! It would come out to circa $30 per board. Not too bad IMHO.

 

Backplane.pdf

Edited April 15, 2021 by ivop