Re: [stella] How to know?

Subject: Re: [stella] How to know?
From: emooney@xxxxxxxxxxxxxxxx (Erik Mooney)
Date: Tue, 16 Sep 1997 04:08:20 GMT
>I took a break from my C64 tool, and decided to just
>use it in it's beta stage to do a little A2600 program.
>It just displays a stable screen (3 lines of VSYNC, 37
>of VBLANK, 192 picture, and 30 of overscan), changing
>one of the playfield registers every line.  Worked my
>first try ;)

I did the same thing for my first project, except that I changed two
playfield registers, and mine took two tries because I didn't set COLUPF
the first time.

>Anyway, this prompts a couple questions:
>1) How do I know I've made _exactly_ the 262 lines per
>frame?  It seems TVs are fairly resilient, and will
>allow at least a few lines of error, with ?no difference?
>visible.  I mean, how can you know without counting
>through it all, and being ?certain?

You answered your own question - TVs are pretty resilient, so you don't
need to do exactly 262 lines.  You're supposed to count through it all and
alternate between 262 and 263 lines (NTSC video is defined as 525.5 lines
every 1/30 second) but most TVs will sync anywhere between about 240 and
about 280.

>2) Why is overscan differentiated from the main 192 line
>display?  Can you not display graphics there?  Should
>you blank the screen for that area?  Is there anything
>special you should do in that area?

It doesn't have to be differentiated, and some games do display more than
192 lines.  Missile Command draws 222.  All TVs will display 192 lines..
more than that and some older TVs may cut off part of the picture.  You can
do whatever you want there... the picture will continue to be displayed
until you write a 0 to VBLANK.

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