Post 9ffc5Rm2xrTOKbCbhI by bhtooefr@cathoderay.tube
(DIR) More posts by bhtooefr@cathoderay.tube
(DIR) Post #9ffY1NsP76frGhz0tc by bhtooefr@cathoderay.tube
2019-02-09T20:12:59.418866Z
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An idea that's been bouncing around my head for a while: a so-called "Mini-XTX" motherboard. I'm not offering to make this, but it's something that I think would be neat to see.This would be a Mini-ITX form-factor motherboard, with the following features:* Switchable CPU speed between 4.77 and 9.55 MHz following the DTK standard for software switching* EMS 4.0 memory mapper, support for 1 MiB, 4 MiB, and 16 MiB 30-pin SIMMs (all memory under EMS control, and a default mapping of the first 640 kiB)* Super I/O chip providing 2x serial, parallel, FDC, RTC, soft ATX power, and PS/2 mouse/keyboard (the SMSC/Microchip FDC37B787 is I think the winner here), although with the caveat that this may require a custom BIOS to handle the keyboard controller properly?* XT-IDE-compatible PATA controller* Two 8-bit ISA slots, one in line with the I/O shield for an extremely low profile graphics card* A 7905 to provide -5 VDC to the cards that need it (in practice this means sound cards), so you can use any modern ATX power supply, you don't need something from the 1990s/early 2000s.Then, the graphics card options, all at 38 mm tall to stay under the I/O shield height and fit into the very tightest of cases:* CGA clone with the target of 100% compatibility with 8088 MPH, and with both TTL (DE9S) and composite (RCA socket) connections. If the design needs a CPLD to work (I suspect it will), maybe also support disabling CGA snow, and support the PCjr/Tandy modes? (If you did that, you'd also want sound support I think, and that actually complicates things.)* MDA clone, with color MDA support (which was a thing!). No need to provide parallel, just the video.* Something VGA, I guess?
(DIR) Post #9ffc5Rm2xrTOKbCbhI by bhtooefr@cathoderay.tube
2019-02-09T20:58:33.891364Z
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One annoyance I thought of with this design: Many Mini-ITX cases use a PCI riser, to flip the PCI card 90 degrees (either above or beside the motherboard).With an ISA slot, however, the slot is .562" further down the motherboard, which is significant enough that an existing case using a beside-motherboard riser will need creative riser design to work properly. (There's a few ways to do it - a metal or plastic frame to support a card on a ribbon cable riser could work, brute forcing it with three PCBs (to push the connector .562" back), or maybe you could cut a hole in the PCB and run the card through the back side of the connector?)If the riser folds the card over the motherboard, though, you just need to space the slot out .562". Not a problem AFAIK.
(DIR) Post #9ffcJR7ICmckLYoJgO by bhtooefr@cathoderay.tube
2019-02-09T21:01:05.254953Z
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Personally, I think the ribbon cable riser might make sense anyway - design the bracket properly, and you could make it adjustable for different cases (as Mini-ITX cases often shipped with their own riser when they need one, so you'd need to adjust an ISA riser for each case design anyway). Basically you'd have a stub of PCB in the motherboard that the bracket would mount to with height adjustability, and you could just flip the ribbon cable's mounting into the bracket to get the connector facing the right way.
(DIR) Post #9fg02lvNzDD4rHpOYC by seatsafetyswitch@cronk.stenoweb.net
2019-02-10T01:21:14Z
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@bhtooefr you could embed a Snark Barker too.
(DIR) Post #9fg02mAz3Dgddf7qrY by bhtooefr@cathoderay.tube
2019-02-10T01:26:59.716292Z
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@seatsafetyswitch That's burning up a lot of board area, though, and I'm not sure how I would feel about embedding a SB on a *XT*, where it wasn't all that useful anyway. (Even an Adlib isn't *THAT* useful...)And, I mean, there's a whole ISA slot free to shove a Snark Barker into, and my ultra-low-profile graphics slot idea would be available for VGA instead of CGA/MDA, if you want to play the VGA+SB Turbo XT game.