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Cruzer
Registered: Dec 2001
Posts: 1048 |
Teletext?
Since a TV generates teletext from some black/white pixels on some unused rasterlines, I wonder if it might be possible to make the c64 generate a teletext signal by putting some bordersprites in that area. Granted ofcuz that the vic chip produces a signal on these lines, and that it's possible with the c64's restrictions to get the right pixels in the right place to get the TV to interpret it as teletext.
Anyone who has experimented with this? |
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Ninja
Registered: Jan 2002
Posts: 411 |
I think it should be possible using the trick to display data in the 2Mhz-mode on a C128. (By the way, I don't know when Graham found this out. At least, Dizzy Devil showed it to me years before RfO).
Plus, I could imagine that at least some teletext decoders don't care in which line teletext data is being displayed. I mean such a check would require extra logic, just checking the run-in-sequence should be way easier. And the German specs say, that those lines for teletext are "recommended". It doesn't say "only there"
Anyway, both approaches are worth a try :) |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Graham told me how this worked and it's not about 2Mhz (yes 2Mhz option is in that register aswell). It's another bit telling the VIC to increase $d012 every cycle as long as that bit is set. In effect everything if offset due to skipped rasterlines. However, I'm not sure that the VIC will display at correct lines even still. And about teletext decoders... the teletext is located in the VBI data (i.e. when the raster beam is moving to the top-left corner). There is ofcourse already logic for handling vertical blank :D so I don't really agree with you there Ninja.
I will be suprised if it works... :D But then again the ways of the c64 are mysterious. |
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Ninja
Registered: Jan 2002
Posts: 411 |
jack: I see, this is the other $d030 issue then. So, we were talking about different things before :)
Still, the specs I have do just recommend teletext to be in the VBI. I don't see a "must" there. I hope this is some kind of backdoor...
But talking won't help us, someone has to try it :) I would do it somewhen, only not now. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
@ninja: :D I agree, talking won't help and also a teletext demo would certainly shake the foundation of c64/c128 demo coding. |
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Hoogo
Registered: Jun 2002
Posts: 105 |
Quote: @ninja: :D I agree, talking won't help and also a teletext demo would certainly shake the foundation of c64/c128 demo coding.
That would shake the foundations... All of a sudden everyone will realize that we did it wrong for 20 years ;-) |
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