I've been working on an emulation of UK Teletext which is the same as Mode-7 on a BBC Micro. I have a horrible feeling I started it this morning and it's only taken me this long... scary. I'll release the source etc. but I want to tidy it up first. Also at some point I'm hoping to convert some routines to ASM because it only just keeps up with itself at the moment. It runs ok on my 1.6GHz Athlon at a res of 1024x768. The reason for the crazy resolution is the fact that on a TV the image is stretched, and to get that effect with no nasty artifacts I had to up the resolution.
Here's a screenshot to be getting on with while I attack the source code:
![[Image: teletext.png]](http://marinedalek.no-ip.com/teletext.png)
The bits that are meant to flash flash and the clock works, but there are one or two features I haven't implemented because I haven't a clue what they do! These are End Box (&H0A), Start Box (&H0B), Conceal Display (&H18), Hold Graphics (&H1E) and Release Graphics (&H1F). If anyone has any idea what these do please say so, so that I can put them in the program.
whee! Teletext, hehe.
Ok, about the buttons. Its been a while since I used teletext, but:
I think Conceal Display is used to uncover and cover hidden sections, used in teletext quizes and whatnot. At least thats what I remember it doing in some mini quiz things I did years and years ago.
If "Hold Graphics" is the same as the hold button I am thinking of, then it means that it stops looping pages from automatically progressing to the next page in the sequence after a set time. Instead, it holds the page until you release it, giving time to read at leisure.
Btw, exactly how much of the teletext pages will it emulate? (Seeing as it is a vast network)
It's ok, I've found a site with nice explanations of the functions here:
http://www.bbcbasic.co.uk/products/bbcwi...cwinh.html .
I'm just writing a "decoder" for teletext signals. It's not fully functional yet. If I had access to the teletext data as broadcast then theoretically I could browse the teletext network just like on a TV. However, I don't know how to get at the data, so unless I find somewhere offering dumps of the teletext network in binary form it's nothing more than an intriguing toy. The page you see was hand-coded.
excuse me for asking, but why did you create a teletext renderer if you have no feed? ;P
And why are you awake at 4am? I thought only i was crazy/stupid enough for that. ;D
Quote:excuse me for asking, but why did you create a teletext renderer if you have no feed? ;P
Because
Quote:And why are you awake at 4am? I thought only i was crazy/stupid enough for that. ;D
4:47am
I should really go to bed now
hmmm
....
*waits*
best do I suppose, so I have a clear head to finish off the renderer.
Then it's on to the much harder task of actually finding a use for it!
I'm quite interested on this. Please keep us up to date.
After skim-reading the datasheet for a Philips decoder, I've decided to make it a pure mode-7 decoder for the time being - no multiple pages, just an interface that accepts control codes etc. to produce a teletext page. I have a feeling the philips decoder does this, only with a front-end to convert the extra data relating to page number etc.
Things left to implement before I release the code: Conceal Display, Hold Graphics, Release Graphics and the rest of the custom teletext character set. At the moment it's the bare minimum ASCII-compliant set.
Program complete-ish. Next thing is the ability to read in a screendump and parse that, followed by full support for a teletext datastream (though where I'll get one from is anybody's guess!)
Download =>
teletext.zip
Man, that reminds me of the Telegazeta in Poland....
