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16bit MFM\RLL + Floppy controller in 8bit PC\XT... possible?

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First post, by Ozzuneoj

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The title pretty much says it all. Would a 16bit ISA MFM\RLL + Floppy card be able to work in an 8bit slot? I'm thinking yes, but I don't know what the side effects would be... the 16bit portion has to do something. I'd only need one hard drive and two floppies accessible.

My reason for wanting to do this is related to a post in another thread... it got me rethinking the idea of putting my Soundblaster CT1350B (hopefully with CMS upgrade eventually) in my IBM 5150 with a 286 upgrade. I know it isn't a perfectly matched system, but I don't own a 386, so it currently serves as my system to play the oldest of DOS games (pre-VGA).

These systems are incredibly limited by having only 5 8bit ISA slots. The slots are currently populated as such:

Slot 5 - Everex EV-659 (EGA+Parallel)
Slot 4 - AST SixPakPlus (384k memory expansion, RTC+battery, 1xSerial, 1xGameport)
Slot 3 - Original IBM Floppy (Connected to 5 1/4 Tandon 360k and 3.5" TEAC for 720k support)
Slot 2 - Western Digital WD1002A-wx1 (MFM controller connected to 20MB Miniscribe drive)
Slot 1 - Orchid Tiny Turbo 286 (Switchable between 8088 4.7Mhz and AMD 7.16Mhz 286)

To add a sound card (or anything else) I'll have to remove something, but they're all integral to the computer at this point, so my only option is to consolidate two cards into one... hence an MFM\RLL+Floppy controller... but they seem to always be 16bit.

Now for some blitting from the back buffer.

Reply 1 of 3, by Jo22

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It depends on the model, I guess. For example, some MFM/RLL controllers do have their own firmware (mostly 8bit ones), some don't.
Besides, PC/XT and PC/AT used different i/o ports for HDD (see XT-IDE). That's no real problem, though.

Afaik, there were also external ISA boxes. But they are now a bit rare to find, I guess.
IBM made one, as well. I think it was named the "IBM 5161 Expansion Unit".
If you do know someone with good soldering skills, you can even make your own.
The PC-BUS is quite simple (~62 pins). A backplane paired with an old SCSI plug (68–pin for example) and
a ribbon cable could be used for expansion. Perhaps you'll need a second PSU (not necessary f. game cards, etc.)
But saying that, I haven't done this myself so far. It's just and idea. So be careful when you really attempt to build it.

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 2 of 3, by h-a-l-9000

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The floppy portion may work. But the HDD MFM part is designed for 16-bit I/O and you are very likely lacking BIOS support (if the card doesn't bring its own BIOS).

1+1=10

Reply 3 of 3, by Jo22

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Good point. I wonder if that XT-IDE BIOS is able to talk to an WD1003 controller, too.

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

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