[retro swim] - Episode 36 (Part 3) - More Teradrive Fun

[@HunterZBNS]

OMG one machine that does composite CGA, plus EGA and VGA?! It should be considered the holy grail of 16-bit PC gaming hardware!

[@BeyondTheScanlines]

That extra ISA slot mod was ingenious. Such a weird computer on so many levels - particularly because of that whole dual pixel clock thing? I have to wonder about that indeed. Been enjoying this mini-series quite a bit :D

[@RetroSwim]

I think there's probably a lot about this computer that isn't documented, or is poorly documented. It's definitely a cool thing! :)

[@Pixelmusement]

Admittedly, I'm not well versed in how ISA works, but how is it all you had to do was add wires and were able to seemingly magically connect a second ISA device to something which was never intended to hold more than one? I would've thought there would be more to it than that in terms of configuration and whatnot. :o

[@RetroSwim]

The ISA bus is very simple in design. All of the address lines, data lines, IRQ lines, and DMA lines are connected to every slot in parallel. It's the job of the card itself to selectively listen for data that it bound for it (which is the purpose of IO ports, the card should ignore the data lines unless the address on the address bus matches what it's configured to). The CPU has no way of knowing which slot an ISA device is connected to, because they're electrically identical.

[@HunterZBNS]

I guess that's pretty much the idea of a bus, but yeah I wouldn't have thought of that either. And even if I'd thought of it, I'm not sure I would have had the guts to try that lol. Nice work!

[@HighTreason610]

Aha, so you've found the no -12V thing, I remember me and some guy on a forum scratching our heads for ages before he remembered the PSU didn't supply negative voltages... We felt a bit dumb for not latching onto this fact so fast. He ended up just using another sound card and I've always left mine as PC Speaker only. Awesome ISA modification there, that must have taken some real patience, what's that, like 78 connections total? Geez.

[@RetroSwim]

39, I saved myself some effort and time by leaving out the pins not used by the XTCF adaptor! :)

[@tom611]

What's the pin header at the top of the ISA for? I'm a bit surprised that you soldered directly to such a rare and fairly expensive machine, I would've used an external expansion box or soldered to the sound card, personally.

[@RetroSwim]

The header is for a proprietary HDD, which was factory fitted in the TeraDrive Model 3. It's the same HDD found in one of the 286 model IBM PS/2 systems. If I needed to solder to the mobo I probably would have looked for an alternative, but I was perfectly comfortable soldering the 0.1" spaced pins on the ISA slot on the riser board.

[@intel386DX]

cool! I did not know that you can add more slots in parallel :)

[@wishusknight3009]

I tried adding a passive backplane to a 386 that I have to give it 8 more slots. It sort of worked.... But sometimes there needs to be proper bus termination and drive signal which I didn't ever get figured out. But yeah it is pretty much as simple as soldering wires, its not PRQ driven like PCI is.

[@ChrisNova777]

wow comander keen.. i didnt even know i did play this game but i just got a WICKID INTENSE flashback of playing that game.. so i guess i did! .. ww i was probably 9 years old

[@RetroSwim]

Awesome! :D