First post, by mockingbird
The XT-FDC is a worthless piece of garbage.
Here are a couple of links that describe the project in-depth:
https://www.vcfed.org/forum/forum/vcwiki/vcwi … 081-xt-fdc-rev1
https://www.retrobrewcomputers.org/doku.php?i … sa:xt-fdc:start
Here are the two boards I built:
One board has used parts in it, and the second board was built from parts ordered exclusively from an authorized distributor (Newark), as all the parts, except for the PC8477B are still being produced and can be obtained. The EEPROM was programmed with the 2.2 BIOS latest and verified with a TL866 vartiant.
The inspiration to build this project came from Tech Tangent's Youtube video titled More than two floppy drives?. In his video, he laments at the end how he didn't use the XT-FDC instead of paying a lot for his current floppy controller.
The truth of the matter is that he is way better off with his current card. The XT-FDC BIOS simply does not work properly, at least not on 486-class PCs. I tested this on both the ECS UM4980 and the Asus VL/I-486SV2GX4. If the card is used as a "dumb" controller (If JP1 is open which disables the boot ROM), it works properly. If JP14 is open, the card won't work with the ROM enabled. When the card does work with the ROM configured, floppy access is very, very slow (maybe this was only tested on an XT).
Even with the card working with the ROM enabled, I could not get the second port to work properly. With a 360K (verified working) drive attached, when accessed as drive B:, the LED comes on but the drive won't spin.
So just a warning for anyone needing a controller for more than two floppies (if your BIOS doesn't support it natively). This is not a good solution. The project seems to have been abandoned, and I haven't seen any new BIOS updates.
What I probably will end up doing is just using these as dumb controllers on two seperate computers and just having only two floppies per computer.