Tuesday, January 12, 2016

Fujitsu-General TXR-21 and VXR-20

In this previous post I just wrote a little about Teletext and Videotex and their relationship. In this other one I wrote about the devices that looks like MSX but are not. This post is the offspring of those two previous posts.

We already talked a lot about CAPTAIN devices. And the only CAPTAIN device that the MSX community knew was, for real, a MSX. And I knew that many times the teletext and videotex share their presentation format. With that knowledge, when I saw the Fujitsu-General TXR-21, I wanted it.

Who's Fujitsu-General?

Fujitsu-General can not be know as a MSX manufacturer, but they have a history with MSX and, at least, two MSX computers released. But when those computers were released the company's name was "General".

General Paxon advertising

In 1985, General was bought by Fujitsu and the company name was changed to Fujitsu-General. The MSX manufacturers list on "MSX2 Datapack" already showed the new name.

Then, we already have two good signs to buy that machine: the only CAPTAIN adapter that we knew was a MSX compatible and Fujitsu-General has the know-how to build a MSX. And then I saw the TXR-21 expansion slot and the cartridges that goes there.

Fujitsu-General TXR-21 (top) and VXR-20 (bottom) frontal view

Back of TXR-21 and VXR-20, you can see the 50-pin slot
connector, (with a cartrige inserted), the printer port
(Centronics 14-pins female), the audio/video out (RCA),
the audio/video (RCA) in and the RGB21 connector.

Didn't this cartridge looks a lot like a MSX cartridge?

They are visually identical to MSX cartridges. Nothing could be wrong and I bought this item.

Well, all could be wrong.

What's inside Fujitsu-General TXR-21?

When I opened the TXR-21, there was only three components that remembered the MSX: the Z80 processor, the slot connector and the sound chip, YM2413.

TXR-21 mainboard: the Z80 is the small square chip at top right
and the YM2413 is behind the huge capacitor

Excluding the EPROMs and RAM, the main ICs are:

Intel P80C31BH: 8051 compatible 8-bit microcontroller
Fujitsu MB64H445: CMOS Gate Array
Fujitsu MB64H448: CMOS Gate Array
NEC 70008A4: Z80 processor
OKI M6254 (MSM6254RS): Don't know what is it
Toshiba TC9017N: Teletext, Screen Display Controller
Yamaha YM2413: FM sound generator, the same of MSX-Music

And that's all. Tabajara picked the two socketed ROMs and dumped their contents using a EPROM reader. Nothing interesting there (at least for MSX research). The strings inside the ROM still says TXR-20:


If you want to investigate those ROMs, they are in this tarball.

From what I could understand, the 80C31 waits in standby (it have a low consumption mode) and when it receives an event (from remote sensor by example), it activates the other board components. The Z80 is the main processor, TC9017 controls the video, YM2413 plays the CAPTAIN tones and M6254 "reads" the teletext data from the broadcast transmission.

That is a "Not MSX". Even the cartridges, while mecanically compatible with the MSX standard, are eletric and hardware uncompatible. The two kinds of cartridges that I have here for the TXR-20/21: one is a big memory buffer to holds many teletext data and the other one is the modem adapter.

The memory buffer

CAPTAIN adapter cartridge

What's inside Fujitsu-General VXR-20


The cabinet is mostly empty, there is a small modem board at the corner. The cabinet size is to make a good looking set with TXR-20 or TXR-21 (they are almost identical)
The modem board, with many dip-switches

The big ICs on this board are:

NEC D7811G - 8-bit, single-chip microcomputer with A/D converter (the datasheet says the bus is 8085 compatible. Is the processor code compatible, too?)
NEC D7720AC - Programmable DSP

Funny story, I bought a CAPTAIN adapter cartridge "for MSX" some time ago and it doesn't works. I guessed it was because some circuit logic could be in the other end of cable (I got only the cartridge) or because it was defective. Now I know why: it's the same cartridge that cames with VXR-20, only the label is different.

My two VXR-20 cartridges
Probably the seller didn't knew what this cartridge was, but it looked like a MSX cartridge, had CAPTAIN wrote at label... and announced as a CAPTAIN adapter for MSX. Nice to see that I am not the only one fooled by those cartridges. I hope this post could help others to not made the same mistake.

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