Table of Contents
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:
- Basic FDC.
- Configurable IO ports, interrupts, and DMA.
- Optional boot ROM.
- Optional ROM drive. (As of May 2013: No supporting software - none currently planned).
- Optional connector for external floppy drive (self-powered).
- Optional use of a DP8473V controller chip in socket U2 instead of a PC8477B controller chip in socket U16.
- Optional use of an 82077AA controller chip in socket U16 instead of a PC8477B. (See 'Known Problems/Issues' section below.)
- 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.
Current Version: XT-FDC Rev 01
Manufacturing Files: Files were not on old wiki
Vintage Computer Forum Links
Note - the Vintage Computer Forums moved to a new URL in February 2016. All links below point to the new URL.
BIOS Links & Files
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 The latest version may be found here in case the files below are out of date.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).
The diagrams below document the jumper settings for the XT-FDC board. Click for larger images. Diagrams courtesy of http://www.minuszerodegrees.net/
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:
- 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.
- National Semiconductor DP8473V - nothing in socket U16, and a DP8473V in socket U2
- 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.
- 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.
- “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
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!
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