Teletext on the C128 40 column screen

Started by OzOne, October 29, 2006, 08:29 AM

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OzOne

Since a TV generates Teletext from unused rater lines might it be possible to make the 128 generate a Teletext signal by putting some sprites in the border ? I understand this would not be possible (at least easily) on the 80 column screen (no sprites!) Of course, can the VIC in the 128 actually put sprites in the border - I seem to recall this could be done with the C64's VIC-II.

Or, is it possible to put text in the border areas somehow ?

Anyone have any ideas ?

Oz

romwack

Even if you can put sprites in the border, this still isn't the 'unused' part of the screen.  

Or can border sprites be placed in this area?  We need someone with vertical hold to test this :-)

hydrophilic

Cool idea.  It should work if you disable the vertical border and stick your sprites up top.  Disabling the vertical border is very easy and doesn't even require a stable raster interrupt.

The VDC should also be able to do it with text.  Just change the vertical sync position to make the screen start way up at the top.  Then you might want to increase the total number of displayed rows so you still have 25 rows in the visible part of the screen.  Finally, to continue using the KERNAL Editor routines, you'd need to set the start of text and start of color to the first of the last 25 rows (since the Editor can't handle more than 25 rows).

With either chip, the horizontal borders might cause trouble, depending on the teletext details.  Anybody want to share a link?  In the case of VIC, the horizontal borders can also be disabled, but this definately requires a stable raster interrupt.