The XT-FDC is an 8 bit ISA board based on the National Semiconductor PC8477B floppy disk drive controller chip, a chip that supports up to four floppy disk drives. It supports up to four floppy drives internally with an optional external connector for two of those.

Hardware functionality included is:

  1. Basic FDC.
  2. Configurable IO ports, interrupts, and DMA.
  3. Optional boot ROM.
  4. Optional ROM drive. (As of May 2013: No supporting software - none currently planned).
  5. Optional connector for external floppy drive (self-powered).
  6. Optional use of a DP8473V controller chip in socket U2 instead of a PC8477B controller chip in socket U16.
  7. Optional use of an 82077AA controller chip in socket U16 instead of a PC8477B. (See 'Known Problems/Issues' section below.)
  8. Optional connector for 8“ drive (no guarantee of suitability).

This board was a project on the Vintage Computer Forum, and a large amount of useful information can be found in forum threads there. See the links in the “Build Information” section below to relevant threads on this forum.

Hardware Documentation

Current Version: XT-FDC Rev 01

Board: printing_xt-fdc-brd.pdf

Schematic: printing_xt-fdc-sch.pdf

Manufacturing Files: FIXME Files were not on old wiki FIXME

KiCAD Files:

Build Information

Note - the Vintage Computer Forums moved to a new URL in February 2016. All links below point to the new URL.

The BIOS for the XT-FDC has been written by Sergey Malinov. The latest version may be found here in case the files below are out of date. (Note that the linked page is for a different hardware board than the XT-FDC; the BIOS works with both boards).

Parts List

Jumper Settings

The diagrams below document the jumper settings for the XT-FDC board. Click for larger images. Diagrams courtesy of

Basic FDC:

Boot ROM:

ROM Drive:

DP8473V in socket U2:

Alternate Controller Chips

The primary intent is for a National Semiconductor PC8477B floppy disk drive controller chip to be used in socket U16. There are two other options:

  1. Intel 82077AA - in socket U16, an 82077AA is used in place of the PC8477B. Note that the -5 version of the chip (i.e. 82077AA-5) does not support 2.88M drives. At May 2013, only one tester has the 82077AA working in the XT-FDC. See the 'Known Problems/Issues' section below for more information. The use of an 82077AA has two unique requirements:
    • Capacitor C23 in place.
    • Jumper JP10 on.
  2. National Semiconductor DP8473V - nothing in socket U16, and a DP8473V in socket U2

Known Problems/Issues

  1. 82077AA chip - May 2013: It was anticpated that an 82077AA chip would work in socket U16. It works in modem7's second-revision prototype board, but not in the second-revision boards of nestor nor Kiwisek. For now, just be aware that there is a risk of the XT-FDC not working if an 82077AA is used.
  2. 360K Drives - Some 360K drives generate a signal on pin 34. For 360K drives that do, that will be a READY signal. A READY signal will be a problem for the XT-FDC. If you intend to connect a 360K drive to the XT-FDC that generates a signal on pin 34, then disconnect pin 34. Some drives have a jumper that can be removed to achieve that (e.g. the JU-455-7 has an 'RY' jumper). For information, that requirement is not unique to the XT-FDC board. The IBM 5162 and 5170 computers have the same requirement. Note: 1.2M drives will be expected to generate a DISK CHANGED signal on pin 34.
  3. “ROM” Errors - the following problem was fixed in version 2.2 of Sergey's BIOS:
    • On the IBM 5150 (later model), the following errors will be seen on computer power on: F660 ROM, F860 ROM, FA60 ROM, FC60 ROM
    • On the IBM 5155 and IBM 5160, the following errors will be seen on computer power on: F6600 ROM, F8600 ROM, FA600 ROM, FC600 ROM

Builder's Notes/Comments

Please use this space to add any notes/comments on this board that don't fit into the above sections. (Periodically, these comments may be re-arranged to be better incorporated into a new revision of the wiki page.) Please sign your comments using the wiki “Insert Signature” feature!

File List

FilenameFilesizeLast modified
28c64.pdf660.2 KiB2016/02/28 13:37
am29f040.pdf241.2 KiB2016/02/28 13:37
dp8473.pdf354.4 KiB2016/02/28 13:37
floppy_bios-2.2.bin8.0 KiB2016/02/28 14:23
floppy_bios-2.2.tar.gz100.4 KiB2016/02/28 14:23
isa_xt-fdc-001.zip128.1 KiB2016/02/28 13:37
pc8477b.pdf573.6 KiB2016/02/28 13:37
printing_xt-fdc-brd.pdf981.6 KiB2016/02/28 13:37
printing_xt-fdc-sch.pdf277.1 KiB2016/02/28 13:37
xt-fdc-components.png86.2 KiB2016/02/28 13:39
xt-fdc.lst6.9 KiB2016/02/28 13:37
boards/isa/xt-fdc/start.txt · Last modified: 2016/02/29 06:36 by tgoodman
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