Exploring EXT FDD port

Started by Cyothevile, March 19, 2021, 04:00:17 AM

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So all tower model and early desktops have the EXT FDD port. This was meant to be used with Fujitsu branded external floppy drives. The pinout is luckily provided in the FM Towns red book. After receiving feedback from ODE tester he gave specifics. He thought a tower model FMT with twin goteks isn't very aesthetic. I would agree with him to be honest. From a preservation standpoint though floppy drive emulators are best long term since floppy is vulnerable to magnetism, water, mold, bending etc. Racing against the clock for floppy preservation.

So I will be exploring possibility of potentially harnessing using that connector in a project. the intent is to use perhaps a PC98 external double floppy enclosure and use twin goteks in it. that way you have your physical drives still in your computer if you want to use floppy or in my case, the floppies I didn't crack the protection on yet :p

So basically, you grab a cheap pc98 double floppy enclosure and rip out the interface board, insert my imaginary board and use SCSI150 to SCSI250 female cable to connect to the PC. It is very important to note that the EXT FDD connector doesn't provide electricity hence the idea to
 a pc98 enclosure... Which does have a PSU and they seem to be very available. I would grab a totally broken one, gut the interface board and floppy and recap the PSU internally.

I'm making breakout board for the EXT FDD port and will be testing pinout to try to get a goteks to interact with the computer correctly. There seem to be some proprietary signals for the specific Fujitsu drives unfortunately which could be challenging and I really hope it could be possible to use simple converter PCB. One can hope. If it boils down to it I will try to nab a EXT FDD for FMT but they're kinda rare.

I will keep you posted.


Recently I won an EXT FDD on Yahoo.

I'll rip it open when it arrives. If the ICs aren't proprietary custom controllers and they're just logic IC as I suspect, cloning this card will be easy.

I also identifies the mating connector and a mass produced cable that can be used with some modification. I will keep you informed.


It turns out EXT FDD was meant for FMR computers, the predecessor to FMT. With proper cables I was able to boot Columns on my grey desktop.
I will begin the process to clone the interface board inside the EXT FDD


Definitely interested in your clone. I have some FMR systems that would benefit from this along with my FM Towns


I just got a CX20 and it looks like both FDDs are no good, so definitely interested in this project.

EDIT: Turns out the drives are fine, bad caps in the power supply were causing the issue. Still very much interested in this project!


To use external FDD you have to set the drives in TownsOS. It can be possible to set the two EXT FDD as the primary FDD by setting the jumpers to 0 and 1, with the internal drives set with jumpers at 2 and 3. That way you can use the external drives as your primary ones.

I promise I'll resume this in the summer.. Currently getting my nuts crushed in this university schedule.

The good news is that the board is just 74 series discrete logic chips so it's very simple. Getting a cable will be harder but possible.