Re: 264 Series and their chips

On 08/14/2011 09:50 PM, Hársfalvi Levente wrote:
> On 2011-08-14 21:14, Gerrit Heitsch wrote:
>
>> Do you have a link giving some background on how that is done? I have
>> seen full screen images on the C16, but so far was unable to find
>> documentation that explains how to do this. Since TED doesn't have
>> sprites you can't do things as you'd do with a VIC when you want to put
>> graphics in the border area.
>
> Border removal doesn't need making use of the NTSC-bit ie. the above
> trick of enhancing horizontal resolution.
>
> Either way, I don't know where they're documented.
>
> In short, removing the vertical border is done by $ff1d tricks (setting
> the raster register back and forth at certain positions, so that screen
> redraw would be started earlier / stopped later than usual (taking care
> of the number of lines per frame that should be kept unaffected), with
> the additional work of switching screen memory at some position where
> the screen memory page would normally run "out" ie. wrap around). On the
> VIC, the possibility of using that trick is prevented by the absence of
> a writeable rasterline counter. Here it's fully possible to "enlarge"
> the screen area (without the chip stopping screen redraw after 25 rows),
> so no sprites are needed either.

Hm, yes, almost forgot that all relevant counters on TED can be written 
to. I can see how one can do neat tricks by using more than one bitmap 
area and adjusting the counters on the fly. Getting the timing right 
must be a pain with the double clocking unless one decides to go with 
single speed at all times.

  Gerrit


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