Re: [stella] to overscan or not to overscan?

Subject: Re: [stella] to overscan or not to overscan?
From: p.cavina@xxxxxxxxxxxxx (Piero Cavina)
Date: Tue, 3 Dec 1996 21:13:34 +0100
>>According to the Stella programmer's guide, a NTSC TV frame generated by
>>the 2600 consists of 3 VSYNC lines, 37 VBLANK lines, 192 TV picture lines
>>and 30 "overscan" lines.
>I allways thought, that you have PAL TVs in Italy too. So the values would be
>3 VSYNC lines, 45 VBLANK lines, 228 TV picture lines and 36 overscan lines.

Yes, we've PAL. The values should be those... more or less! I found the
right ones by try and miss. :)

>>The question is: do we really need to do the "overscan" lines?

>You have to do the overscan lines, because they are part of the TV frame. You
>can get a steady picture without them, but there is a high possibility, that
>you will get the wrong colours or no colours at all, if you don't do the right
>number of lines for all parts of the TV frame.

That's true, in fact just one line too much can cause the colours to
disappear or the frame to flip.

>The overscan is the part from the end of the visible TV screen to the end of
>the actual TV tube. Since there is nothing to see there you can simply
>skip them
>by setting up a loop, that does STA WSYNC 30(36) times.

It seems to me that it's no easy to say where the visible TV screen ends,
maybe this changes from TV set to TV set?

>because there is no time for game logic during the 'TV picture' part of
>the TV frame.

I learned this very soon... :(

Thanks for your help


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