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Old 24 April 2020, 23:07   #1
Gorf
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Is the Amiga capable of Teletext?

Well ok: there are several hardware thingies, that allow decoding of teletext/videotext - that is NOT what I am talking about.

I am wondering if the other way around, producing a teletext signal for the TV, is actually possible, even if I am not aware of any such project or tool ....

Here ist a RaspPi doing it (without additional hardware!)
[ Show youtube player ]
https://github.com/ali1234/raspi-teletext

Could a ECS Amiga be tweaked to display something during the phase that would be otherwise "vblank"?

Last edited by Gorf; 25 April 2020 at 04:44.
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Old 25 April 2020, 01:05   #2
Solo Kazuki
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Software on AmiNet.
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Old 25 April 2020, 01:28   #3
Gorf
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Originally Posted by Solo Kazuki View Post
I did of course look there (and other places) BEFORE I started this thread.
And none of these programs do, what I asked for!

So your comment is not helpful at all!
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Old 25 April 2020, 02:12   #4
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he wants to transmit it to a TV, confusing because the video shows old UK Ceefax
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Old 25 April 2020, 03:35   #5
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Originally Posted by Retro1234 View Post
he wants to transmit it to a TV, confusing because the video shows old UK Ceefax
Ceefax=teletext=videotext

the video shows just pages done with the same technique, but the signal comes from the RasPi.

Now: could the Amiga do the same?
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Old 25 April 2020, 04:16   #6
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My Microtext disk for my adaptor contains a drawer called developer and includes application software that allows software to be written. Such applications to be written in Lattice 'C'. It says that the routines are provided for your own private use only. There is an object file displayrow.o which provides a means of displaying teletext pages on an Amiga screen.


https://www.scuzzscink.com/amiga/scu...ary19_2603.htm


You should refer to the 1976 Broadcast Teletext Specification which is published by the BBC. They give a phone number though this is 1988.


I do sense that the software and developer tools are designed to work with the adaptor which is the key I guess to providing the data. Dunno.
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Old 25 April 2020, 04:33   #7
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I have this vague memory of one of the DICE games actually having a teletext signal in it? Or am I completely lost here?
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Old 25 April 2020, 04:40   #8
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Originally Posted by scuzz View Post
My Microtext disk for my adaptor contains a drawer called developer and includes application software that allows software to be written. Such applications to be written in Lattice 'C'. It says that the routines are provided for your own private use only. There is an object file displayrow.o which provides a means of displaying teletext pages on an Amiga screen.


https://www.scuzzscink.com/amiga/scu...ary19_2603.htm


You should refer to the 1976 Broadcast Teletext Specification which is published by the BBC. They give a phone number though this is 1988.


I do sense that the software and developer tools are designed to work with the adaptor which is the key I guess to providing the data. Dunno.
Again: wrong direction!
This adapter is for decoding teletext and showing the results on your Amiga.

I was asking for sending out a teletext signal from the Amiga to any TV that is capable of displaying teletext.

Yes I am referring to the official teletext standard.
The system was called Ceefax in UK, Teletext in France and Videotext in Germany. But all three use the same standard.
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Old 25 April 2020, 04:41   #9
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Originally Posted by NorthWay View Post
I have this vague memory of one of the DICE games actually having a teletext signal in it? Or am I completely lost here?
Ok that is the first real hint, that it might be possible!
What DICE game are you referring to?
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Old 25 April 2020, 05:55   #10
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In analogue TV, Teletext, and programme guide data, is encoded in the vertical blanking period between frames.

That Raspberry Pi project fiddles with the registers of the video output hardware so that the top of the display buffer is output into the normally blank part of the video signal and then renders the teletext data as a bitmap. It only works with the analogue composite video output, not HDMI.

I'm not sure if the Amiga HW can be made to do that. A good place to start is probably the stuff on overscan in the HRM like http://amigadev.elowar.com/read/ADCD.../node006F.html. Like with the RPI, this will probably only work for composite or (urgh) RF TV inputs.

A few years ago I was working for a place that was still using broadcast teletext in retail locations but the broadcaster wanted to shut it down. I was on a team that won an in-house hackathon by prototyping a RPI teletext solution based on that github repo. It got picked up as a real project and I spent a couple of weeks with another guy writing a much neater version in C# that could talk to the rest of our systems but that was the end of my involvement. It was a fun bit of work

Andrew
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Old 25 April 2020, 06:29   #11
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Quote:
Originally Posted by bwldrbst View Post
In analogue TV, Teletext, and programme guide data, is encoded in the vertical blanking period between frames.
Yes. I thought this was clear

Quote:
That Raspberry Pi project fiddles with the registers of the video output hardware so that the top of the display buffer is output into the normally blank part of the video signal and then renders the teletext data as a bitmap. It only works with the analogue composite video output, not HDMI.
Exactly

Quote:

I'm not sure if the Amiga HW can be made to do that.
Well - that was my question.

Quote:
A good place to start is probably the stuff on overscan in the HRM like http://amigadev.elowar.com/read/ADCD.../node006F.html. Like with the RPI, this will probably only work for composite or (urgh) RF TV inputs.
No sure - it should also work via RGB (SCART) I think. Probably depends on the TV.

Is there an overview what is possible with ECS timings?
(OCS won’t work for sure but there are quite some strange settings possible with ECS)

Quote:
A few years ago I was working for a place that was still using broadcast teletext in retail locations but the broadcaster wanted to shut it down. I was on a team that won an in-house hackathon by prototyping a RPI teletext solution based on that github repo. It got picked up as a real project and I spent a couple of weeks with another guy writing a much neater version in C# that could talk to the rest of our systems but that was the end of my involvement. It was a fun bit of work

Andrew

I did not know that someone still actively uses teletext.

My idea was, this could perhaps be a missed opportunity for the Amiga ... for applications like the one you coded for - and of course as a second display that could be used in parallel. That would be ideal for things like video-titeling ...
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Old 25 April 2020, 08:31   #12
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Quote:
Originally Posted by Gorf View Post
No sure - it should also work via RGB (SCART) I think. Probably depends on the TV.
Probably. I've never actually seen a SCART TV, they weren't really sold here.

Quote:
Originally Posted by Gorf View Post
Is there an overview what is possible with ECS timings?
(OCS won’t work for sure but there are quite some strange settings possible with ECS)
I've had a bit of a look in the HRM. The VBSTRT/VBSTOP registers sound like they may be relevant. They might allow display of lines in the area reserved for teletext.

However in this thread there seems to be some doubt that it's possible: http://eab.abime.net/showthread.php?t=50015

Quote:
Originally Posted by Gorf View Post
I did not know that someone still actively uses teletext.
As far as I know, they're one of the last users of it. They're a betting company that used it for race information displays at racecourses and in retail outlets. They're gradually phasing it out but needed a temporary solution for when the broadcaster turned it off.
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Old 25 April 2020, 11:28   #13
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The wikipedia page on teletext says the following about teletext encoding:
Quote:
Originally Posted by Wikipedia on Telextext
...using lines 6–22 on the first field and 318–335 on the second field...
So we'd need an display setup that can hit PAL lines 6-22.
The HRM states the following on vertical blank & maximum overscan
Quote:
Originally Posted by amigadev.elowar.com on vertical blanking
The minimum time of vertical blanking is 20 horizontal scan lines for an
NTSC system and 25 horizontal scan lines for a PAL system. The range
starts at line 0 and ends at line 20 for NTSC or line 25 for PAL.
Quote:
Originally Posted by amigadev.elowar.com on maximum overscan
Code:
                              NTSC                 PAL
                              ----                 ---

     Vertical Blank Start     0                    0
      Vertical Blank Stop     $15 (21)             $1D (29)


                              NTSC     NTSC        PAL      PAL
                              Normal   Interlaced  Normal   Interlaced
                              ------   ----------  ------   ----------
        Displayable lines
          of screen video     241      483         283      567
                                       =525-(21*2)          =625-(29*2)


        Table 3-13: Maximum Allowable Vertical Screen Video
I'm pretty sure the numbers mentioned here count scanlines the same way as the Wikipedia article does. Which means that (unless I really misinterpreted the HRM or it is wrong) the answer is sadly: no, not without additional hardware.
Edit: above is info for OCS only. I don't know about ECS/AGA here, as I've never used the extra registers mentioned in the post above.

Last edited by roondar; 25 April 2020 at 11:37.
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Old 25 April 2020, 16:14   #14
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Dutch national television still uses teletext. One of the very few, I'll bet.
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Old 25 April 2020, 16:15   #15
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yes I am aware of the OCS limitation in this case ;-)

Here is the same question from a couple of years ago with a short answer from Toni:
Quote:
teletext data lines are blanked by default. Need custom vblank timing settings. (this should be easily solved)
http://eab.abime.net/showthread.php?t=39670

Toni sees problems with the encoding ... but got wrong numbers there, which is discussed here:
http://eab.abime.net/showthread.php?t=50015
(from comment #17 on)

And here some discussion about the maximum overscan:
http://eab.abime.net/showthread.php?t=45691

All in all: no definitive answer. Nobody actually tried.
I don't have a CRT anymore ... got rid of them because I moved a couple of times and they are no fun to carry around
Actually I do not have a TV set at all (just monitors) or anything that would be able to display teletext ...

So it will probably stay a mystery forever ....

Last edited by Gorf; 25 April 2020 at 22:00.
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Old 25 April 2020, 19:38   #16
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Originally Posted by Gorf View Post
I don't have a CRT anymore ... got rid of them because I moves a couple of times and then are no fun to cary around
Actually I do not have a TV set at all (just monitors) or anything that would be able to display teletext ...

So it will probably stay a mystery forever ....
Very interesting topic! I cannot contribute any experience with teletext on the Amiga, but if you want to investigate further, maybe get an old USB TV dongle? There are ones that support analog TV with teletext, e.g. the Cinergy Hybrid ones. They show up on ebay quite often for a couple of Euros, and seem to have Linux support. Anyway, I'd guess it would turn out to be a massive time sink...
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Old 25 April 2020, 20:10   #17
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Originally Posted by chb View Post
Very interesting topic! I cannot contribute any experience with teletext on the Amiga, but if you want to investigate further, maybe get an old USB TV dongle? There are ones that support analog TV with teletext, e.g. the Cinergy Hybrid ones. They show up on ebay quite often for a couple of Euros, and seem to have Linux support. Anyway, I'd guess it would turn out to be a massive time sink...
They would need some input connectors I could actually use ... otherwise I would need a RF-modulator for my A3000 to feed that dongle.

It is also unclear if rgb would work ... the RaspPi it the video outputs composite ... so would BW-composite be enough?

PS:

that link is just for "DVB-T" dongles ... they expect a digital signal to begin with...
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Old 25 April 2020, 20:15   #18
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Quote:
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What DICE game are you referring to?
I have this faint memory that Benefactor might have had it, but I can't for the life of me remember where I have picked up on that.
Was there any other late DI(CE) game?
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Old 25 April 2020, 20:16   #19
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Originally Posted by Hedeon View Post
Dutch national television still uses teletext. One of the very few, I'll bet.
Probably as alot of TV is received through a box connect to a TV via HDMI and Text doesn't work via HDMI and probably only works with PAL/SECAM not HD.

Although you Neighbour Belgium has some of the most cable TV in the world and I'd be surprised if there cable TV isn't with HDMI.
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Old 25 April 2020, 20:23   #20
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I have this faint memory that Benefactor might have had it, but I can't for the life of me remember where I have picked up on that.
Was there any other late DI(CE) game?
The only "game" I am aware of is Worms - but the teletext-version of that game was just an April joke from Team17

https://www.team17.com/worms-for-tel...-marvel/worms/
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