VOGONS


First post, by starhawk

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I have a stack of weird reasons stuck together that makes me want to do this. Please don't ask unless you want a response so long it will have numbered chapters, AND you're willing to read something that's that long. No, I can't condense it, don't ask for that -- I will cackle, tell you that you were warned, and hand you a novel that you can expect to be quizzed on.

I have a datasheet for an Intel 82335SX chip that (theoretically) can take a 16MHz or 20MHz i386SX CPU and i387 FPU, and make it work in a system that expects to greet an 80286 when it gets up in the morning. I've attached it. Unfortunately, while I can get the chip from a questionable source in China (for the usual caveats, including a price that makes me wonder just how high the odds are that I'll be getting an experience similar to Sparkfun's early 2010 experience with Not Alibaba... especially considering that there are *four* *listings* *on* *all* *of* *eBay* and of the four, this is the odd one out at *half* the price of the others!) -- I can't find ANY schematics for how to use it, nor can I locate any modules/daughtercards/etc that are prebuilt that use it.

To be completely honest, the track record I have with putting circuitry together and having it actually *work* means that whether or not that chip is actually a chunk of bare copper flattened hard and stuck in a 132pin QFP probably doesn't actually matter much.

But I want to try.

Specifically what I want to make is a daughterboard that will adapt a 12MHz 286 motherboard to a 20MHz 386SX + a matching 387 coproc. I don't mind bodge-wiring the existing motherboard to heck and back if I have to, and I have a spare for it, but I basically want to "286-Overdrive" (as if such a thing ever existed by that name) the system in question. If it absolutely matters, the machine I'm upgrading (or trying to) is a Compaq Portable III, and I want to do it in a way that respects the era and heritage of that machine. This is *NOT* getting a RasPi inside; those people make me as close as I ever get to violently angry. A 20MHz or 25MHz 386 is about perfect for me -- my very first system of my own rocked a 25MHz AM386SX and that turns out to have been an incredible coincidence, because that's right about at the sweet spot for me where computing just makes sense. (Funny how that works.)

Laugh at me if you want, but can anyone find me that ref design... or *any* schematics that will let me build what I describe?

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Reply 2 of 18, by Oetker

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Have you looked into existing boards that do the same thing? These devices exist and aren't as special as you seem to think they are. One of them might be using the same chip, maybe someone that owns one could provide you with more info.
Hyper386sx 286 Upgrade CPU
Re: 286-to-386...or...286-to-486 Adapters...GOT ONE??
Looking for 286 CPU upgrade "kit"

Reply 3 of 18, by wiretap

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You likely won't find implementation schematics, because those are property of the OEM who designed boards with them and probably still under proprietary release exemptions. Looking at the datasheet, it is actually very detailed and goes into all the necessary voltage requirements, current requirements, capacitance, resistance, AC/DC timings, wait states, logic timing charts, etc. For interfacing other devices, you need to also look at their datasheets for the respective requirements so you can design a circuit that meets the electrical spec.

Your best bet is to reverse engineer a schematic from an existing board if you don't know where to start based on the data sheet. These Intel 82335-SX chips did come on some early Shuttle motherboards from what I see on CPU registries.

Regardless, if you don't know where to go from the datasheet, a hardware design of this level would be a monumental task that would have an extremely high chance of failure. You won't be able to do it with bodge wire.. it is way too complex. Even simple CPU upgrade boards for the Amiga that interface with the 68000 take years to develop from very skilled individuals that know hardware engineering like the back of their hand or have been in that industry for many years. A 286 to 386 interface with coprocessor will more complicated than that.

Here is what a 8088 or 286 to 386+coprocossor upgrade board looks like -- The Intel InBoard 386: http://www.cpushack.com/2019/08/14/how-to-386 … inboard-386-at/

edit: as the post above mine, there are also the later-era upgrade boards that adapt to the existing socket.

Circuit Board Repair Manuals
EGA 120 Column Project
MHz Display Project
Dual Socket 8 Project

Reply 4 of 18, by starhawk

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Hmmm...

Right, they're not so uncommon... sure... off to eBay, then, since that's where nearly all such stuff always is -- at least in my experience! (Note, ignore the quote marks, they're used here to delineate search terms, they weren't part of the actual search because I have more intelligence than an empty can of store brand baked beans. Duh.)
"hypertec 386sx" --> No matches found. (FWIW, the *only* HyperTec brand /anything/ of even remote relevance is an ISA-8 RTC card. Meh.)
"evergreen technologies" --> One result, not relevant (an upgrade for non-super Skt7 motherboards to support a 333MHz K6-II CPU, if I understand it. I didn't look that close because I didn't care enough.)
"SX/20LCM" --> No matches.
"SX/25LCM" --> No matches.
"SX/33LCM" --> No matches.
"kingston 286 386" --> No matches.
"intel inboard" --> No matches.

Right... exactly as I'd pretty well figured. @Oetker, I know I'm "special" and I'm starting to think that you might be as well 😉 but I'll not issue summary judgement. Do me a kind favor, if you would, please -- since you're apparently privy to knowledge I've not got, where is a place I can find these things, that more ordinary folks normally would not go? Clearly you know better than I do!

Reply 5 of 18, by megatron-uk

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The kit isn't exactly rare, but it's not common either. The IBM PS/2 range has a whole suite of proprietary 286 to 486slc modules from Kingston, for example. (I have one myself, but most of them won't work in anything else than the system they were designed for)

The devices so come up on eBay, but we are talking about 30 years old kit that would have sold in the tens of thousands range, rather than hundreds or millions, so you won't see them everyday.

Reply 7 of 18, by starhawk

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@Megatron-UK -- OK, three questions. One, is it reasonably possible (or even UNreasonably possible without swapping the entire freaking PCB or programming a whole new ROM -- I do some crazy stuff with electronics and I'm kinda known for it in my more usual circles, but it keeps me in the black bank-wise) to make eg a Kingston PS/2 unit work in a different system? Two, is there anywhere even a little less exclusive than chip-collecting sites? and three, about how much should I expect to pay? 😒

I've never even actually seen one listed on eBay.

Reply 9 of 18, by Tiido

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The short answer is that this info will never come / doesn't exist.
Longer answer is that when you know how the 286 and 386 buses work, the datasheet of that chip provides enough info to build the thing you're after. Most of it made sense when I went though the datasheet and there shouldn't be too much difficulty getting things going.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 12 of 18, by pentiumspeed

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https://www.ebay.ca/itm/Vintage-AMI-386-386SX … CYAAOSw7elf84hZ

The data sheet does this exactly as this motherboard is.

Cheers,

Great Northern aka Canada.

Reply 13 of 18, by starhawk

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/sigh

Correction...

starhawk wrote on 2021-02-28, 00:36:

For newcomers: any suggestions for obtaining an "accelerator card" (for lack of a better term) as could be built with the chip in question or something like it, other than eBay or specialist chip-collector places...?

Again, relevant system is a Compaq Portable III, 12MHz 286 CPU -- goal is 20MHz or 25MHz 386 CPU.

Off topic --
As an aside, forgive me for noting... but, speaking strictly as a 34 y/o Millennial... a lot of knowledge and a lot of inspiration comes from actual physical books, even still -- and as a collective species, once such things are gone, if that ever happens, we will be much the worse for it. Maybe I sound like an Okay Boomer, but think about what books have made a difference in your life -- Tracy Kidder's "The Soul of a New Machine" anyone? or a dusty old programming manual? or even an ancient print encyclopedia...? Learn to scroll and to read large bodies of text and to be okay with that. I firmly believe that we could, as human beings communicating with one another nearly constantly across the globe, a vast quantity of the civil unrest in the world today could've been avoided if we'd not limited ourselves to 140 characters -- or 160 of them, for that matter -- in each such message we send, and especially by not trying to reinvent hieroglyphics to compensate for the failures of trying to cram far too much information into far too little linguistic space. Verbose communications are good for you and it has indeed been scientifically proven -- there's an article in Medium about it. Medium is one of those sites with anti-adblock measures ("free article" limits), so I have a PDF copy if anyone is interested. PM me; this is not the place for that discussion 😀 and I don't want this thread hijacked any more than it already is.

Reply 14 of 18, by Horun

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Ahhh a Compaq Portable III ! Nice. Cannot find any schematics but have a question: If you had an Evergreen 286 upgrade style adapter will it fit in your Compaq ?
You want to build your own but will a retail old style pre-built fit in your Compaq ?
Most of the CPU upgrade adapters are specifically designed and if you did not look these over it may give a little help (but now schematics):
http://ps-2.retropc.se/sandy55/Interposer/386_upgrade.html

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣 Second computer a 286 12Mhz with real IDE drive ! After that came 386, 486, Pentium, P.Pro and everything after....

Reply 15 of 18, by starhawk

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@ Horun -- if you can get me pinouts I can make it work. Might take a bit of work with the ol' logic probe, Compaq didn't leave behind proper documentation. But I have the same squawk pen that Blondihacks (Quinn Dunki) uses, and she's done some pretty amazing stuff -- I'm no Blondihacks but I'm also not the dimmest indicator light on the side of the box, either 😉 and I'm one stubborn git -- if it can be made to work, I'll argue with it till it does or till it smokes.

FWIW, the Compaq Portable III uses a sort of clamp-down socket thing for the CPU -- it looks, and works, remarkably like a modern Intel LGA socket except without the 'window' in the middle of the lid... and the fact that it's a lot harder to pry the 286 version open! But there are also a lot of proprietary Compaq chips on the mobo. I can get you photos but it's gonna be a day or two, I'm trying to tidy up the apartment a bit, and the machine is in the back of a closet right now.

Also -- Horun, PM me how much you'd want, including shipping, for the thing -- I have to be very careful with budgeting, but if we can work something out in the next few days, I'll be able to pay you in early March. I just have to plan ahead a little, that's all 😀

Reply 16 of 18, by starhawk

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@ Horun -- any luck on pinouts? I can't see much on that linked page -- unfortunately the thumbnails go to a 404 page 🙁 of course if I'm being an idiot and *all* it needs is the CPU socket (I can't imagine it's that simple tho) then no problem. But if it needs more than that I'm gonna need to know that, and I'm gonna need details.

@ Everyone else -- can you help as well? Pinouts, better photos, etc. Mostly I just need to know how it connects.

Reply 18 of 18, by Horun

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I do not own a 286 interposer upgrade anymore. It disappeared sometime back in the past 🙁

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣 Second computer a 286 12Mhz with real IDE drive ! After that came 386, 486, Pentium, P.Pro and everything after....