8235 External FDD port: how to use it

Luck has it I received a """new""" diskdrive by mail yesterday and what better way to test it than with a 8235.
The drive was hardwired as B: drive.
The computer is modded with a double sided disk rom and rewired to actually be able to work with double sided disk drives. The rewiring is at least necessary for internal double sided drives. I'm not sure if the external drive requires it as well.
I used a default 34 pin data cable (no twists or whatsoever) from an NMS8250 and some power from an ATX PSU.

The drive turned out to be ok, so it's an A: drive now and got installed in another computer.

I've never tried and I don't have all flavours (roms/drives), though my guess is that a virgin 8235 can only handle single sided diskdrives. I've heard otherwise, but I've never seen it happen.
There are tutorials on how to mod your machine to work with double sided drives.

Have you tested what your internal drive does on the external connector? You do need a cable adapter for that, but they're available.

Hi all
Thanks for all helps and advices.

In the end I succeeded to use the external fdd connection of my VG-8235.
Now I put here some details hoping they could be useful to some other ones like me.

I've found the solution for my case here: CREDIT

I've the model VG-8235/20 so I've also connected the CN3 PIN6 to the CN15 PIN10: probably this connection could need to say to the ext fdd to become S0 and the internal fdd to become S1 ... but I'm not sure for this.

Then I've done by myself a Shugart ribbon cable, starting from a PC ribbon cable, and I've paid attention to invert btween themeselves the PIN 10 with the PIN 12.

I've done the first test with a Gotek configured for MSX:
hot=msx and interface = jc into the ff.CFG file and jumpers put to close MO and S0

I've noticed that both the internal fdd and the external Gotek were running when I were doing the commands FILES or RUN "A:" or RUN "B:".
Then I've used the POKE comand:
first test using POKE &hf247,0 to set the default fdd to Α:
second ones using POKE &hf247,1 to set the default fdd to B:
but I had always the internal fdd running.

After these first test the loading from Gotek didn't work anymore: I don't know if could be caused by my ribbon Shugart cable or because the cooesistent internal and external fdds. The connection adviced between CN3 PIN6 and CN15 PIN10 probably does not exclude the internal FDD.

So I've removed the power supply of the internal fdd to exclude it.

After this action the Gotek connected to the external port worked properly again:
it lets the boot from some disk images, such as MSX Hme Office, EASE and other games selected from Gotek

Here I've put some videos about my tests:
Boot test1 from Gotek https://www.youtube.com/watch?v=tPbpLfVHQMk
Boot test2 from Gotek https://youtu.be/dDj2Z7dqfH8
Boot test3 from Gotek https://youtu.be/2LYVB-5eIZk
Boot test4 from Gotek https://youtu.be/cxesFXrrcmM

The Next step will be:
1) to set a switch for choosing the exclusion of the internal fdd when I use the external fdd port
2) test a real fdd device such as the VY-0010

Pin 10 and 12 of the external connector are the drive select signals. Pin 10 is drive select 0 (or A: for us humans) and pin 12 is drive select 1 (B. The Gotek drive will listen to one of these signals, depending on its jumper settings. If you have put the jumper on S0 it will react to drive select 0, if you have put the jumper on S1 it will react to drive select 1.

Apparently the drive select 0 is not connected to the external connector in a 8235/20, that's why you had to make a connection between CN3/PIN6 and CN15/PIN10.

Switching the wires in the ribbon cable is only necessary for drives that don't have jumpers like these. If your drive is hardwired to be A: it will be connected only to drive select 0. By switching the wires you reroute the drive select 1 to that connector pin and that drive can be used as B:.

I use a straight 1:1 ribbon cable to connect the Gotek to the external port of my 8235/00 with S0 jumper set. It works fine, the internal drive has been disconnected as it is broken anyway.

By the way, have you replaced the diskrom of your 8235?

Hi Briqunullus,
I've tried using a straight 1:1 ribbon cable, before all these tests, but nothing: both Gotek (S0 or S1 or nothing) and the external floppy driver, a VY-0010, only could read the disk contents and nothing all. No run, no load , no boot... nothing ☹️ ... only disk off line message from the prompt.
When I've inverted pin10 and pin12 all worked fine instead.

I didn't replace the diskrom: I have the original one. I want to use the original internal floppy and together an external floppy, because an external port was provided for this model