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The Official Nabu PC Floppy Disk Controller thread


Veteran Member
Nov 22, 2012
Richmond Hill, Ontario, Canada
I've had multiple people ask me for pictures of the Nabu PC floppy disk controller (FDC) board so that reproductions can be made. I was a little hesitant to let too many people have pictures because for one, I cannot get mine to work yet and two, there would be duplication of work. I have been convinced that it's best just to put the pictures out there and hope someone can reproduce this board (actually two boards) for the community of new Nabu PC owners.

This is a thread to have any hobbiest discuss this here so we can all learn from questions and answers and maybe get some assistance from others to help figure out why my floppy disk controller doesn't work. It's actually not too complicated but there is a couple of things to note:

1. Any NABU PC can utilise this board set but it needs a modification to the motherboard to allow for the 8K Rev B FDC EPROM to work as opposed to the 4K Rev A EPROM that does not have the FDC functionality.
2. I have posted my Rev B FD firmware.
3. I did my best at the pictures. If you need any further details, please ask here so that everuone can benefit from the answers.
4. If you want to test this out, I would be happy to try a board to see if it acts the same way as my original board and I would appreciate a copy of the board when completed, if possible.

The pictures and information are posted here: https://vintagecomputer.ca/nabu-pc-fdc/

Disk images and firmware are located here: https://vintagecomputer.ca/files/Nabu/ Note: Thanks to Dave Dunfield for the images. I put a copy here

Please ask any questions here and if you do decide to tackle this reproduction, please post here to let evryone know who is working on it. I would like to try to avoid duplication of work but I realize this is a hobby and people may want to do the reproduction on their own. Let's hope this work can benefit all new Nabu PC owners.

P.S. If you have a working Nabu PC with a working floppy drive, please contact me.
Wow! you are one of the 0.1% of people who not only post pictures, but made the extra effort to desolder the chips from the board so we can see all the traces! I'd hate to ask this but could you provide the dimensions of the boards?
Ask away. That's what this thread is for :)

The FDC main board is 231mm x 85mm. There are two holes for standoffs that match holes in the motherboard. One in the middle and one at the far end. You have the dimensions for the metal plate. Same size and screw holes.

The FDC Option board is 88mm x 52mm. It's held in by the pins.
Very nice work @snuci . Between this effort and the effort to reverse engineer the network adapter, I’m convinced that something really interesting will be possible with all of these NABU PCs.

- Alex
I got a start on this after talking with @snuci on twitter just after these machines started surfacing on ebay. Learning that the bridgeboard pulls all 4 slot select signals has been important. I'm slowly rebuilding the schematic from pictures - at first I thought the FDC directly attached to J9. The WD1797 has been replaced with a WD2797, which doesn't require 12V and is a better part in general.


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I noticed that the connector board for the floppy controller utilizes all four options slots. It seems to take all of the card select and interrupt lines from each of the headers, and puts it in one cable. Looking at the pictures, I assume this is to allow additional expansion options to be daisy-chained to the floppy adapter instead of connecting directly to the mainboard.

Unless the floppy controller is using multiple interrupt vectors or more than 16 I/O addresses, I wonder if it is a good idea to keep this feature in reproductions. If additional homebrew expansions are developed in the future, it may cause some issues. Either cards would need to be designed to daisy chain off the floppy controller (making it a requirement that the floppy controller is present to use), or other expansion options and the floppy controller would not be able to be used at the same time.

I am currently working on a design for an IDE ATA adapter for my unit when it shows up. It would also be nice to be able to use the floppy drive controller, if the option is available.
I use the IDE board from the nabu.cpm project here: https://github.com/randomvariations/nabu.cpm It requires you to tap into the TR1863 to communicate to the Nabu via a USB to TTY interface and a PC terminal (no use of the Nabu video or keyboard). I am able to boot up CP/M 2.2. Unfortunately, it doesn't work with the FDC at all at this point. I was going to see if I could use the 30 pin connector off of the FDC board to see if I can run both FDC board and CF IDE but as one can see, the 30 pin option port is not extended untouched through the FDC card.

If you haven't seen this picture, this is how the IDE CF card is connected and the wires coming off of the TR1863 for input/output.
I did see that project, but the interface strategy they are using will only work for CF cards and the (more rare) XT-style hard drives. It is designed to use the 8-bit XFA, while I am designing around the 16-bit ATA bus. That should allow both 8-bit and 16-bit devices to be used without issue. It also isn't too that much more complicated, only requiring latching buffers and some more addressing / chip select logic.

As for the 30-pin connector on the FDC, it looks to be wired differently than the 30-pin connectors on the board. From what I can see with the images you posted, the floppy controller only consumes the CS and INT lines from slot 1, and passes the signals in slots 2, 3, and 4 onto the external header.
@ThisPostContainsComputers yeah, my guess would be that it uses more than one address - but I haven't got to the part where I check that just yet. One *should* be sufficient, but this card is built in a very strange way. If you look, for instance, at the LS244 closest to the 30-way headerr, it has D0-7 going *out* of it, but the inputs all seem to go to ground!?
And yes, the bridgeboard changes the pinout of the 30-way header. For instance, it doesn't pass 5V.
Been poking at the software side. It looks at CF/DF/EF/FF for 0x10 to find the card

By the look of it

x0 is then control/status
x1 is sector
x2 is track
x3 is data
xF reads 0x10, bit 1 of write looks like it may be the motor poking bit
bottom underway, i know people will build modern better versions, i like to have a close replica also. i still need to go over it with a fine tooth comb from the high res imagesfdc bottom.JPG
@Klyball, are you duplicating @snuci’s board exactly and then adding the jumper wire and cutting the trace just like @snuci’s board? Or will you mod the traces to incorporate the fixes applied to @snuci’s board?