MattInX's Miscelaneous Musings Say what now?


Retrochallenge Half-Time Round-up

Well, I meant to write this up at the weekend, but that didn't happen. Better late than never - it's time for a half-time round-up, or perhaps a review of quite how much has been added on to my to-do list for this project. It really does seem to be one of those things where it appears complicated at first, then you get into it, and discover there's a significant number of smaller tasks you hadn't thought of to begin with. Despite the mamoth amount of work outstanding, it's actually been a pretty productive first half of the challenge, and I'm certainly enjoying it.

I started off with a laptop that whilst technically could boot, couldn't do so under its own power, and couldn't run with both hard disk and floppy drive at the same time, which made the prospect of investigating the bus rather difficult. That being said, chewing through datasheets and poking at the board did yield quite a bit of useful information. Getting a working PSU was a big first step, and with luck there's a workable schematic for the charging circuitry that I'll be able to test and put together a PCB for so I have a working replacement for the factory PSU. I've been able to get a breakout board for the disk interface put together, although the information I'm getting from that is raising more questions than it answers - but that's the topic of my next post.

What should have been low-hanging fruit - setting up a wiki to document everything - turned into a whole series of issues. First I got into the whole question of what wiki to run, then the dependency game with various library and plugin versions. Finally ending up with the decision that I really just need to bite the bullet and bring my server up to the latest long-term supported release of the OS. I didn't want to do that without making sure we had good backups, which apparently exposed a minor issue with my provider, which they then had to fix. Essentially it's what I see on a regular basis at work, and I'd rather be playing with the retro hardware 🙂

So what's next?

First up is a write-up on my initial tests with my break-out board, which should be coming very soon. That's just opened up a whole new can of worms which has me on the hunt for someone locally with some more test equipment I can use - stay tuned for more!

As I mentioned above, I do have the parts to test the charger circuit I reverse engineered earlier in the month, so testing that seems like a good plan - before commiting that design to a PCB and having it manufactured.

I've been able to identify most of the ISA bus signals required for an XT-IDE interface on the disk controller chipset, which means they're almost certainly present on the connector. I need to ring out those connections and see if I can identify the missing /MEMW line (although this isn't a show-stopper - it's just required for programming). Once that's confirmed - it should be possible to adapt the XT-IDE design to build a new disk controller which would be compatible with Compact Flash. As Victor didn't seem to use a different bottom molding, a CF adaptor could be mounted where the hard disk currently goes, which would allow the card to be accessible through the hole for the second floppy.

That expansion header on the back is still largely undocumented, but once I have the disk controller pinout identified, finding those signals on the expansion header should be fairly straightforward. The 80C86 pinout I have, likewise the pinouts for the latches and buffers on the motherboard. That should make it possible to most (if not all) the remaining signals.

With that said - time to crack on. I should have the next post about the 26-pin interface up soon.

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