VOGONS


Micro ATX 486 - what's the degree of interest?

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Reply 100 of 123, by LightStruk

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jakethompson1 wrote on 2020-09-06, 21:41:
johnnycontrario wrote on 2020-08-29, 06:17:

Coincidentally, I found this product (probably unobtanium), that's almost exactly what I just described: https://www.esapcsolutions.com/product/esa-in … hared-pci-slot/

I have one, if there is anything you'd like to know about it.

I am very curious about the SoC on that board. Have you ever run the DOS Benchmark Pack on it? Does the video chip work well with the typical SVGA and VESA modes?

Which reminds me, I've run that benchmark suite on a Vortex86 MX, a Geode LX, and a VIA Nehemiah, but never posted the results...

Reply 101 of 123, by jakethompson1

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LightStruk wrote on 2020-09-08, 15:57:

I am very curious about the SoC on that board. Have you ever run the DOS Benchmark Pack on it? Does the video chip work well with the typical SVGA and VESA modes?

Which reminds me, I've run that benchmark suite on a Vortex86 MX, a Geode LX, and a VIA Nehemiah, but never posted the results...

I haven't run the benchmark pack but I did run speedsys a while back - Re: The Ultimate 486 Benchmark Comparison you will see that it has no L2 cache, and despite being PC100 the memory timing is a bit disappointing. The BIOS has no options about memory timing. Perhaps the ZFx86 datasheet has info on how to crank it up. My recently-arrived UM8881/UM8886 board runs circles around this thing.

The board has UltraDMA and other modern features, but there is no DOS driver. The UltraDMA controller has some glitches that seem to block it from working with a "standard" DOS UDMA driver. If you look at the patch for Linux on the ZFx86 website for this IDE controller there is info in the comments.

The onboard VGA does pass the Commander Keen test but I haven't done much otherwise. By default it scales everything to 800x600 as if it's designed to drive an LCD screen but you can write an int10h hooker to disable that (I did). However, there is no Win 3.x driver for it, so I put in an ATI Rage XL in the PCI slot and I think that's a better solution.

Reply 103 of 123, by Cyberdyne

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If NuXT is over 300, then i think that a ATX (486) (ISA) would cost over 1000 easily, so it is not economical. Even overpized 486 motherboards are 10 times cheaper.

Just use underclock or throttle or disable cache with your ATX Socket7/Slot1/Socket370.

I am aroused about any X86 motherboard that has full functional ISA slot. I think i have problem. Not really into that original (Turbo) XT,286,386 and CGA/EGA stuff. So just a DOS nut.

Reply 104 of 123, by LightStruk

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Nitroraptor53 wrote on 2020-10-09, 05:21:

I might be getting some money soon. Hypothetically, would anyone design the board? How much?

There are lots of PCB design services on the web you could hire. If you're serious about hiring somebody on this message board to do it, (and there are several clearly skilled engineers who frequent this place), then you should make a separate post where it's clear in the title that you are hiring.

I will reiterate my earlier suggestion. Use the AMD Elan SC520 - you don't need a hard-to-source CPU socket or Northbridge chip. Just a Super I/O chip, SDRAM slots, ISA and PCI slots, IDE ports, and some odds and ends like the PS/2 ports, serial and parallel ports, front panel pin headers, lithium battery socket, floppy port, voltage regulators, BIOS chip, and an ATX power supply socket. The design challenge will be simpler and cheaper if you don't integrate anything else, and the final product will be cheaper too. Testing and validation will be easier.

There are many things you could integrate for creature comforts - an SD2IDE, a sound chip (either an ES1868, YMF71x, or YMF74x), a video chip, and a network chip (some cheap PCI Realtek). On the other hand, all of these creature comforts are already cheaply available as expansion boards! Half of the fun for many customers will be choosing these parts and assembling the end result themselves. Even without everything integrated, a MicroATX board would still have enough slots to get the job done.

Last bit of advice - this is not the kind of board that can be populated by hobbyists. You wouldn't be able to sell this as a kit for people to solder themselves. Whether it's the SC520 or a CPU socket, both are BGA parts that require a reflow oven to solder.

Reply 105 of 123, by Nitroraptor53

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LightStruk wrote on 2020-10-09, 13:38:
There are lots of PCB design services on the web you could hire. If you're serious about hiring somebody on this message board t […]
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Nitroraptor53 wrote on 2020-10-09, 05:21:

I might be getting some money soon. Hypothetically, would anyone design the board? How much?

There are lots of PCB design services on the web you could hire. If you're serious about hiring somebody on this message board to do it, (and there are several clearly skilled engineers who frequent this place), then you should make a separate post where it's clear in the title that you are hiring.

I will reiterate my earlier suggestion. Use the AMD Elan SC520 - you don't need a hard-to-source CPU socket or Northbridge chip. Just a Super I/O chip, SDRAM slots, ISA and PCI slots, IDE ports, and some odds and ends like the PS/2 ports, serial and parallel ports, front panel pin headers, lithium battery socket, floppy port, voltage regulators, BIOS chip, and an ATX power supply socket. The design challenge will be simpler and cheaper if you don't integrate anything else, and the final product will be cheaper too. Testing and validation will be easier.

There are many things you could integrate for creature comforts - an SD2IDE, a sound chip (either an ES1868, YMF71x, or YMF74x), a video chip, and a network chip (some cheap PCI Realtek). On the other hand, all of these creature comforts are already cheaply available as expansion boards! Half of the fun for many customers will be choosing these parts and assembling the end result themselves. Even without everything integrated, a MicroATX board would still have enough slots to get the job done.

Last bit of advice - this is not the kind of board that can be populated by hobbyists. You wouldn't be able to sell this as a kit for people to solder themselves. Whether it's the SC520 or a CPU socket, both are BGA parts that require a reflow oven to solder.

I've never done a project like this, so this seems like good advice. The problem with the Elan, which I have considered as an option, is supply. There's a hundred on ebay but I was wanting to create more than that. There are also 486 sockets on ebay, 564 in total, but I'd probably buy half that. Maybe the board could have a switch between Socket and Integrated? Y'know, switch between the Elan or a user CPU? I imagine there'd be different board configurations, one with an Elan, one with a Socket, one with both, etc, etc.

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Reply 106 of 123, by LightStruk

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Nitroraptor53 wrote on 2020-10-09, 18:19:

The problem with the Elan, which I have considered as an option, is supply.

There's literally hundreds of thousands of SC520's available from distributors on DigiPart. One of them claims to have over 190,000, and will sell them for about $10 each. That's in addition to the smaller, though possibly cheaper, lots listed on eBay.

Nitroraptor53 wrote on 2020-10-09, 18:19:

Maybe the board could have a switch between Socket and Integrated? Y'know, switch between the Elan or a user CPU? I imagine there'd be different board configurations, one with an Elan, one with a Socket, one with both, etc, etc.

It would need to be different board configurations, to the point that they are entirely different products.

  • The Elan SC520 has an integrated Northbridge to talk to PCI, ISA, and main memory. The Socket 3 486 chips all need a traditional chipset with a Northbridge and Southbridge.
  • Socket 3 chipsets run at bus speeds of 25 or 33 MHz and support FPM or EDO RAM, while the SC520 uses the more modern SDRAM running at a bus speed of 66 MHz. The RAM sockets are totally different.
  • Socket 3 CPUs need an L2 cache for optimal performance, which means either more sockets or more chips for you to find. A MicroATX board starts to feel a bit cramped. The SC520 does not support L2 cache, but the faster main memory compensates for that.
  • All of these differences mean that the BIOS will be quite different between the configurations.

Reply 109 of 123, by maxtherabbit

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LightStruk wrote on 2020-10-09, 13:38:

Whether it's the SC520 or a CPU socket, both are BGA parts that require a reflow oven to solder.

PGA 486 sockets are not BGA parts. They are through hole. A skilled hobbiest could easily assemble a traditionally designed 486 board. The most challenging thing would be the fine pitch QFPs used by the chipset

Reply 110 of 123, by LightStruk

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maxtherabbit wrote on 2020-10-11, 16:30:

PGA 486 sockets are not BGA parts. They are through hole. A skilled hobbiest could easily assemble a traditionally designed 486 board. The most challenging thing would be the fine pitch QFPs used by the chipset

I stand corrected. That said, the 237 "through hole" pins on a Socket 3 are quite a bit smaller than the legs of a DIP part, and they are quite close together. I'd be interested in hearing how someone might sanely hand-solder such a thing. Wouldn't it be hard to keep the tip of the iron from bumping into adjacent pins from the one you're working on?
Soldering the fine-pitch QFPs is challenging, but certainly I've seen people do it with just a soldering iron and the appropriate application of flux and solder paste. I have never tried, personally.

Reply 111 of 123, by LightStruk

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pentiumspeed wrote on 2020-10-10, 19:52:

pentiumspeed, this presentation talks about the "Elan SC520 Microcontroller Customer Development Platform" motherboard towards the end. The interesting thing about this board is it looks almost EXACTLY like what I'm proposing. It has 2 SDRAM slots, 3 PCI and 2 ISA slots (one slot shared between the two types), a Super I/O chip (in this case, an ALi M512x providing floppy, LPT, 2 high-speed COM ports, keyboard, and PS/2 mouse), one IDE channel, one ethernet port (provided by an AMD PCnet-FAST III chip, naturally), and a bunch of development aids, like in-circuit emulator, JTAG port, etc.

The biggest problem with this design is the single slow IDE port (no Ultra-ATA here). It's very easy to provide a slow IDE port, since it's just an extension of the ISA bus. It would be much better to have two UDMA33 channels, which could easily be provided by a PCI controller card or by a PCI IDE chip on the board.

Too bad AMD doesn't appear to have posted the schematics of this board anywhere, because then designing a modern MicroATX board would involve only trivial modifications. (Embedded CPU manufacturers sometimes provide schematics of their evaluation boards, as an aid to builders.)

Reply 112 of 123, by appiah4

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Soldering a Socket 3 is not a big deal. Desoldering one? I tried it once, and it was madness.

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Reply 114 of 123, by Thermalwrong

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I did this recently for a dead 486 board 😀 Madness sure, but really good desoldering practise too. Data pins get heated for 2 seconds (can see a small trace going to it) and power pins get heated for 10 seconds. With a good desoldering pump, even a manual one, very do-able.

The 486 socket is pretty roomy compared to later socket types, it's got regular 2.54mm spacing on the pins and the pins of the socket are usually much smaller than the holes they go into, so they're comparatively easy to clear.

Reply 115 of 123, by mattrock1988

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So I was directed to this thread by another kind member of the VOGONS community.

As we have all seen with the NuXT project from our friends at Monotech, there is indeed a market for so-called reimagined retro motherboards, and systems based on them. However, with the rising prices of 486 and Pentium motherboards, I feel there needs to be a more capable board that accommodates either Socket 3 or Socket 5 chips (depending on the desired direction of this project).

Could I get a tally on who might be interested? Perhaps we should put out a proper survey to see what kind of features and capabilities would be desired here. Personally, I'd like to continue along the vein of NuXT... a motherboard that offers some quality integration, but without losing the essence of "retro" (full bevy of ISA slots, compatibility with a wide range of existing Intel, AMD and Cyrix chips, etc).

The more I read through this thread, the more I've begun to side with the more practical concept proposed by LightStruk. The AMD Elan would be more than sufficient for the task, and nearly everything else should be attainable "off the shelf" without relying on super expensive FPGAs. I'd love to see a project like this come to fruition, and will be following this thread (and others like it) with continued interest.

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Reply 116 of 123, by LightStruk

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In the spirit of providing another option, although I think it would be harder to design, harder to source parts for, and perform worse, there is a way to get a genuine Intel i486 with L2 cache support that doesn't require a Socket. Intel manufactured SQFP versions of the DX4-75 and DX4-100 for a while. The best versions appear to be the SK099 and SL2M9 models, which run at 100 MHz and have write-back L1 cache.

As a reminder, using a chip like this means you need the rest of a typical 486 motherboard's chipset (preferably a later one with PCI support), and you would want to provide L2 cache sockets as well. At 100 MHz with slower RAM than the Elan SC520 but with the benefit of L2 cache, it would perform only a little bit worse.

New-old-stock CPUs from this line are out there; here's some DX4-75 (SK052) chips which are either selling for $30 each or 25 cents each - it's unclear if the seller is unloading these one at a time or one box of 120 units at a time. Digipart lists a few distributors with DX4-100 (SL2M9) units in stock, but no prices are published.

Reply 117 of 123, by LightStruk

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@Nitroraptor53, I don't know if you're still pursuing this, but I did a bit more digging into the Elan SC520 and discovered a couple of limitations. They don't make it completely unsuitable for a MicroATX build, but they are important to note.

First, the SC520 only supports two ISA DMA channels, but can be numbered as desired. A typical 486 gaming PC would use at least three: 1 and 5 for a SB16, and 2 for the floppy controller. If there's a ECP/EPP parallel port instead of just a standard bi-directional LPT port, that would normally use channel 3. Strictly speaking, a modern system does not need a floppy drive, although a 486 usually has one. There's always SHSUFDRV for making a virtual floppy drive in software. It might even be possible that a floppy drive and the sound card could share a DMA channel, especially if they are not going to be used simultaneously. As for the parallel port, ECP and EPP are nice to have if you're plugging in a Zip drive or scanner, but again, not really crucial. PCI LPT chips exist and would side-step this issue.

The Elan SC520 Customer Development Platform we talked about earlier has a Super I/O chip with a floppy controller and an EPP parallel port wired to share one of the two available DMA channels.

Edit: Looks like I misunderstood. The SC520 supports four ISA DMA channels. The SC520 Customer Development Platform dedicates two of those four to the Super I/O chip and the IDE interface (see page B-4 of the manual.) A 16-bit sound card would use two channels, which would leave none free. To spare one more DMA channel, using a PCI IDE interface instead would ensure that the second of the two ISA slots has a DMA channel available.

Second, the SC520 does not support ISA bus mastering by expansion cards at all. The MASTER signal is completely missing. ISA SCSI cards and the like would not work, although PCI SCSI cards would work just fine.

The takeaway here is that the Elan SC520 can be the basis of a nice 486-class gaming PC, but it won't have all of the options that a typical 486 motherboard has. If the goal is to make an "ultimate" microATX 486 motherboard that is all things to all people, then the Elan SC520 is not suitable.

Reply 118 of 123, by fosterwj03

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Hi all,

I just watched the Youtube video below about a micro-DOS build and it reminded me of this discussion. He used a processor module with a custom PCB for IO.

https://www.youtube.com/watch?v=aJEp4ZUG7BI

While this isn't an Intel 486, I thought someone could create a full ATX or micro ATX PCB to host one of these system modules (they have both PCI and ISA bus interfaces) to route IO to an ATX back panel and bus lanes to ISA and PCI slots. Some of these modules also include an IDE interface. You could use an ATX power connector to supply power to the board. Just a thought.

Edit: Oh, and since it's a custom board, you could provide the power inverter for -5V right on the motherboard.

Reply 119 of 123, by weedeewee

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fosterwj03 wrote on 2021-04-13, 18:20:

I just watched the Youtube video below about a micro-DOS build and it reminded me of this discussion. He used a processor module with a custom PCB for IO.

https://www.youtube.com/watch?v=aJEp4ZUG7BI

fyi, you mean rasteri in this thread Tiny Vortex86-based DOS gaming PC - weeCee

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