Rick's b.log - 2018/08/15
You are 18.221.90.184, pleased to meet you!
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Rick's b.log - 2018/08/15 |
| It is the 21st of November 2024 You are 18.221.90.184, pleased to meet you! |
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mailto: blog -at- heyrick -dot- eu
For those who don't know what Minitel is, think Prestel. Or videotex. Only it was wildly popular in France, to the point where adoption of the Internet was initially slow in France because people preferred (and trusted) Minitel. When I first came over here to France, it was quite common to see adverts quoting a four digit phone number, like "
Its origins are an experimental project in Brittany in 1978 that was rolled out to the rest of France in 1982, to become the largest and most popular pre-internet online service.
The service is correctly called "Télétel". "Minitel" is the name of the terminal, and it actually has a meaning other than the diminutive size of the terminals - Médium interactif par numérisation d'information téléphonique.
On the back of my Minitel is the specification plate. Interestingly there is an embossed version underneath, with this metal plate placed on top. The end of guarantee, 1988/30 refers to week 30. In other words, the week of 25th July. When the movie Cocktail with Tom Cruise was popular. The first Die Hard movie was released ten days prior, and it's the week Tandy announced the 1000SL computer (an IBM clone running an 8086 at 8MHz, one of many of their "1000" PC clones). I know my model was built in the beginning of January 1986 (from arkings on one of the boards inside). That would be a couple of weeks before the terminal mission of Space Shuttle Challenger. Popular in music was "West End Girls" by the Pet Shop Girls. Sometimes you're better off dead, there's a gun in your hand, it's pointing at your head, you think you're mad too unstable, kicking in chairs and knocking down tables, in a restaurant in a West end town, call the police there's a mad man around, running down underground, to a dive bar in a West end town...
The interesting thing here is he description of the two modes. Mode 1 is CEPT Videotex at a text resolution of 40×25. Again, not unlike Prestel or Teletext (including the block graphics). Mode 2 is more interesting. It's a plain ASCII (ISO 2022/6429) terminal at a resolution of 80×25.
I think it would be rather amusing to debug software on my Pi using a thirty two year old Minitel! Unfortunately it will probably be a while because the Minitel's serial port is "weird" which means that an adapter board needs to be built that uses transistors to switch according to the serial data. One cannot simply plug in an RS232 cable.
The Minitel was ridiculously easy to open. Two clips under the handle, and two underneath. Flip them, then the back would normally slide off. It's a little harder in reality because there's a clip-in mains filter board (with fuses) that needs to be dealt with first to release the mains and telephony cables.
An interesting thing about the video/power board, asides from the big wire patch to the transformer, is that many of the test points and all of the adjustment points are named, actually built into the board design.
Now for the control board. There's no overall image as I have not stripped the machine, and there's plenty of dust as I didn't want to touch the circuitry any more than was absolutely necessary. Anyway, here are the three most important ICs:
The final chip in the photo is a D4168C 8KiB "XRAM" (an SRAM with improvements) hat acts as the memory and screen buffer for the EF9345.
Other ICs on the board are TIC MODEM (HC3 5731-R) and TIC FCC (M04 8801?). All I can say that you can still by the modem chip from China, and searching for anything with "FCC" in the title is going to end up being something to do with the American FCC...
Not pictured is one 5V voltage regulator with a heatsink. At a rough guess, this will be stepping down the 8V from the video/power board to the 5V used by the rest of the motherboard. Being built in the '80s, it will be 5V TTL logic levels.
Now here's something new. I've seen Minitels before. I've seen inside Minitels before. I haven't seen this before...
The keyboard is a membrane matrix. Nothing unusual about the electronics. In terms of keys, there are three primary sections. The alphabetic keys (like a regular keyboard), the numeric keys (like a phone - with 123 at the top), and special function keys: Connexion/Fin, Fnct, Sommaire, Annulation, Retour, Répétition, Guide, Correction, Suite, and Envoi.
Reassembly was simple. Just put the back cover back on, clip into place, and refit the filter board.
David Pilling's Hearsay 2 has a Minitel emulation, with source as Main.c.vxterm. Pop over to David's site for the software/source.
Minitel 1B
Another public holiday (Assumption), another vide grenier. This time, I picked up an ancient Minitel 1B made by Telic Alcatel.
3634". Minitel progressively expanded to include colour and graphics primitives, however like Prestel it used the videotex style 1200/75 data transfer rate.
Around the turn of the century, France Telecom estimated that there were 25 million users of Minitel (out of a population of around 60 million), and about ten thousand companies provided twenty five thousand different services - all accessible through the little Minitel terminal. As with Prestel, some services were free and some were paid. The range included messaging services, directory enquiries (always free), adult services, plane/train booking, and mail order companies. In 1998, Minitel generated revenues of €832,000,000, of which €521,000,000 (yes, half a billion euros) was channelled to the many service providers. This was 1998. When reasonably fast (33k6 (56k would arrive in 1999)) dial-up with local rate phone numbers was available.
Minitel was finally switched off in 2012, which was big news here in France.
The service operated at V.23 which means it is a half-duplex data transfer that receives data at 1200 baud and sends it at 75 baud. Being half-duplex, data only flows in one direction at a time. This is contemporary with similar systems such as Prestel, but it's somewhat extraordinary that users in the early 2010s had the patience...
The terminal is entirely passive. That is to say that it is a screen and a keyboard and little else. A very small amount of firmware decodes the input data or display and encodes the keyboard for transmission. There is no storage and precious little memory. There is a method of printing the screen (to compatible serial printers), but that's it. The remote system does all of the work, the Minitel just acts as the human interface end.
Sorry. In case it wasn't blatantly obvious (uh, all over this blog), I grew up in the '80s so all this is the stuff of my childhood memories.
It doesn't work that way from switch on. One needs to press 
Fnct T then A (select Terminal American) to switch to 80×25 mode, then Fnct P then 4 to switch the serial port to 4800bps (the fastest this machine can do). Finally, Fnct T then E to toggle local echo off.
The serial port is 7E1, so don't expect support for extended characters. Indeed, one can select between American and French terminal types, and this alters what characters are available. Being 7 bit, only values 0-127 can be sent to the terminal.
Apparently the terminal does emulate a traditional protocol. Some think it is VT100 compatible, others think it is VT52.
Once inside, the machine is laid out pretty clearly:
The monochrome video tube is pretty obvious. It's a Samsung 240AG4 9 inch black and white cathode ray tube. To the left of the picture (right side in the box) is the video controller and power supply board. This board is connected to the motherboard by way of a seven pin header. It provides +/- 12V and +8V to the motherboard, and accepts composite video and sync from the motherboard. In theory one could inject separated 50Hz video and sync (decoded from PAL if necessary) into the video controller to have the screen act as a display device.
At the bottom is the motherboard. This is where the clever stuff happens. In common with '80s technology, it has numerous integrated circuits.
The biggest IC on the right is an 8032, an Intel microcontroller with no ROM and 256 bytes of RAM. It is an enhanced version of the popular 8051 microcontroller, though like the 8051 it takes 12 clock ticks per instruction cycle. Running in tandem with the video hardware at 14.31818MHz, it achieves approximately 1 MIPS.
This microcontroller decodes the keyboard and the incoming serial data. From that it instructs the EF9345 what to display on the screen.
The ED9345 (closest in the photo) is, really, the heart of how Minitel works. As you can probably imagine the microcontroller is somewhat limited in what it can do with merely 256 bytes of RAM. The EF9345 is a single chip colour CRT controller. It supports 25×40 or 25×80, along with 128 alphanumeric and 128 semi-graphic generators. In 40 character mode it supports foreground/background colours, double height/width, blinking, inverted, conceal etc (a lot like Teletext). In 80 character mode it supports underlining, blinking, reverse, and colour selection (I don't know how much of this Minitel supports). The display can be roll-up, roll-down, or cursor.
Something to note here is that the character generator outputs sync and R, G, B. The R, G, B are mixed together to generate a video signal for the monitor. If one could tap into these, they could be output to a SCART socket for display by compatible TVs. As a cheap'n'cheerful test, it ought to be possible to mix together one of the colour signals with the sync using diodes, shove in a resistance of around 75 ohms or so, and push it into the composite input of a television - not a great way to do it but should work as a proof of concept. You can't mix all the colours using diodes as colour video doesn't work like that. ☺
The Minitel, internally, is colour. Because the hardware works in colour. The screen is monochrome because it's cheaper that way. I have been colour Minitels. Probably later versions.
There are also various logic gates and such, much as expected. Somewhere there will be a V.23 modulator/demodulator. This may well be the function of the TIC MODEM.
There doesn't appear to be any hardware for DTMF tone generation, so it may dial by loop disconnect using the on-hook relay. I would say that such a thing isn't going to stand a hope of working with VoIP phone lines, but then one isn't going to get far trying to push an analogue data signal down a compressed stream.
Holding an 2764, it's an 8KiB EPROM. For what purpose? Easy! The other Minitel 1Bs that I have seen have contained a 8052 microcontroller which contains 8KiB of ROM baked into the chip. If you noticed above, I specified that this microcontroller held no ROM. Thus... here is the firmware. In a separate ROM.
The keyboard is not terribly pleasant to use. Marginally better than the Oric-1. About the same as a graphical calculator. It is laid out in AZERTY format (this is France), with extreme eccentricity regarding the accented characters typical in French. Ctrl-Répétition will get you the œ ligature (which I think is only used in a handful of words), Ctrl-Retour gets it uppercase. Ctrl-Suite gives you the ß which isn't even French (unless France loved Betamax?). Ctrl-Correction would give you a lower case C with cedilla. God help you if you wanted an accented 'e' (any type). I think Ctrl-number gave some other stuff, but there's no indication on the keyboard. And when in American mode? Different characters... no French.
David Pilling, 17th August 2018, 16:06 David Pilling, 17th August 2018, 16:11
Doesn't seem much else.
I suppose I could say "hey is all the Micronet stuff archived somewhere" - also chucked.Rick, 18th August 2018, 21:39
Whereas we might call it "VT100 terminal emulation", the French call it "Le standard téléinformatique"...Rick, 18th August 2018, 21:44
Sorry. I cannot test. Not only do I not have an analogue modem any more (well, I lie, I have my original 14k4 Courier but the power pack is long gone), I also do not have a phone line capable of handling data. It's a virtual landline coming out of the Livebox. VoIP and SIP...
(so I can't test the real Minitel either)David Pilling, 24th August 2018, 01:37 Rick, 8th September 2018, 07:20
[I think Minitel 2 is the first one that supports dialing by itself]marcel ohanian, 22nd March 2021, 03:38 Rick, 22nd March 2021, 19:22
Also, if you had a Minitel, you no longer got phone books (because you can freely use your terminal to look up addresses).
No idea how much they cost new, if for example you wanted to upgrade to a better model? Looking on Google just gets me a hundred thousand terminals on eBay...Peter Renaud, 31st March 2021, 02:09 Rick, 1st April 2021, 14:41
My EPROM programmer worked with my Acorn A5000 and I've not switched that on in two decades. Don't know if it still works...
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