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PC-98 – 110-Pin Cables And External I/O

This was something I had always wanted to try: I had my trusty PC-9801N NS/A and the 110-pin port worked, as I'd tested it with both an Ethernet Adapter and SCSI Adapter.

What else can you do with this port? Well, it turns out that it's a full interface to the PC-98's C-BUS. I mean, that's why the Ethernet and SCSI adapters work so easily... they're actually mini C-BUS cards built to fit the portable asthetic of the 98-Note and its 110-pin connector.

It turns out that NEC released an entire external chassis, known as the PC-9801N-08 External I/O Unit, to hold three C-BUS cards. This connects to any 98-Note with a 110-pin port (later 98-Notes have a much larger port!) via a chunky cable, of which I've never seen one in the flesh. What I have seen are 110-pin to Floppy Drive cables, but these have a centronics 50-pin plug at the far end, instead of the required 110-pin at both ends.

The moons aligned: The right items appeared on Buyee at the right time for the right place... so I collected them.

Can I make a cable?

I set off to find the appropriate 110-pin connectors, but the best I could gather were 'external floppy cables' for the 98-NOTE. Fortunately, these have the correct connector on one end!

Look at that tiny-centronics goodness! Before-long, I had the casing off and the plugs dismantled with minimal damage.

The plastic casing can be prised off...

As expected, the floppy interface didn't need to use all pins, so only a small amount of wiring existed. The plugs are actually crimp-style, so further dismantling occurred to get them apart.

Ok, we're torn-down with minimal damage... a few broken clips, but nothing structural! I grabbed the nearest 50-pin IDC SCSI ribbon and tried to make it fit...

And it was never going to work as the cable was too thick. I couldn't think of viable alternatives... so I went down the solder route. DON'T DO THIS!

I ended up wrecking that plug, so jumped back on the auction site and shelled out too much for yet another 110-pin to floppy cable... it's in the mail.

The proper way to re-wire!

I ended up murdering a few data cables, that had been happily chilling in my box'o'junk, whilst looking for appropriately-girthed wires of a proper length. First up was a 50-pin Centronics SCSI cable... how could that not be tiny-strand?

Crap photo... but that far-left light-blue is the SCSI wire and you can see it's double the thickness. What else? Apple Serial cables were also too thick...

And then I hit the gold mine! DVI cables! Who doesn't have 6 million of the ugly things sitting in a box? And so I got started...

Some of the internal wiring of the DVI cable was twisted pair, probably for the colour video signals. These could still be used, you just needed to strip back more shielding...

The wires locked in to the rail nicely and even happily bent 90-deg, as required for the plug.

And look at that! It happened. I then realised I hadn't recorded the colouring, or even started on the other end... so I had to BEEP OUT the entire thing to wire it up. I mean, this was also a good quality verification process!

Meanwhile, as that I'd murdered the plug for the other side with solder, I couldn't even finish it. 75% done though!

Why was it never going to work?

Whilst waiting for the next cable to arrive, I decided I should investigate the I/O Unit end. Whilst beeping out the pins on the 110-pin connector, I realised that both extremeties of both rows of pins were ALL grounded. ALL GROUNDED. Looking at the pinout of the 110-pin port, these should all be +5v or other signals.... there's no way that these should be grounded on the I/O end?

A quick further googl' pointed out the obvious. In this Japanese forum post, one user asks if they can connect the unit straight through and is quickly told (via googl's bad translator):

However, looking at itp's post, it seems that there are cables (2 pieces) and an interface adapter for the expansion box. Without this, it is practically impossible (to connect a laptop directly). If you look closely at the connector on the back of the I/O Unit, it is not 110 pins. The manual says "100-pin connector".

It's what?

Haha... that's one of my 110-pin Ethernet modules lined up against the 100-pin (Yes, NOT 110-PIN!) connector on the I/O side. All that hard work above was NEVER going to work. Then again, maybe I'll finish the cable as it could still function as one-of-two of the cables needed if I ever manage to find/build the interface box! But then I'll still need a 100-pin amphenol plug!?

We'll chalk this one down as a huge (mildly-expensive) time-sinking failure!