NTSC VIC 20 visible screen size

Basic and Machine Language

Moderator: Moderators

Post Reply
aeb
Vic 20 Amateur
Posts: 67
Joined: Sat Jun 19, 2004 2:06 pm

NTSC VIC 20 visible screen size

Post by aeb »

Quick question - On NTSC unexpanded VIC 20 do you get all 30 lines visible on your screen with these pokes:

poke36865,8
poke36867,188

If not all lines are visible, then how many? (You can count the 7 lines of garbage). Can you make more lines visible on your monitor by making 36865 smaller than 8?

Just asking for a small project; I want to make it NTSC compatible, but it needs 30 lines... (An old VIC-I document said there's not enough raster lines, but VICE emulator shows 31 in NTSC mode.)

Image
User avatar
tokra
Vic 20 Scientist
Posts: 1120
Joined: Tue Apr 27, 2010 5:32 pm
Location: Scheessel, Germany

Re: NTSC VIC 20 visible screen size

Post by tokra »

Sorry, maxmium resolution on a real NTSC-VIC-20 is 233 rasterlines, which I just measured with a 1084 that has a vertical-squeeze knob:

http://sleepingelephant.com/ipw-web/bul ... 9&start=17

Realistically you will only be able to put about 200 rasterlines (= 25 character lines) on screen and be safe on most display-devices with NTSC. Also see pixel's thread in the Games-section for arukanoido where he faced the same problem with NTSC.
aeb
Vic 20 Amateur
Posts: 67
Joined: Sat Jun 19, 2004 2:06 pm

Re: NTSC VIC 20 visible screen size

Post by aeb »

Thanks for the quick response. Maybe 29 will be enough... :) Have you measured the pixel ratio? VICE suggests 0,833 (as in my emulator screenshot), but when comparing to real life VIC video captures (and how I remember it) something like 0,750 would be closer?
User avatar
tokra
Vic 20 Scientist
Posts: 1120
Joined: Tue Apr 27, 2010 5:32 pm
Location: Scheessel, Germany

Re: NTSC VIC 20 visible screen size

Post by tokra »

29 character lines will only be visible on display devices that allow for vertical squeeze, not on more common devices like TVs and such.
Somewhere around 26-27 character lines would be the usual limit for NTSC, see here:

http://sleepingelephant.com/ipw-web/bul ... f=2&t=7189

Also, you seem to be using a very old VICE-version. I suggest trying a recent one from http://vice.pokefinder.org

You will see that NTSC-aspect ratio is 0.752 there
User avatar
pixel
Vic 20 Scientist
Posts: 1330
Joined: Fri Feb 28, 2014 3:56 am
Website: http://hugbox.org/
Location: Berlin, Germany
Occupation: Pan–galactic shaman

Re: NTSC VIC 20 visible screen size

Post by pixel »

tokra wrote:Also see pixel's thread in the Games-section for arukanoido where he faced the same problem with NTSC.
Most of the time I add useful information such as this to the Denial wiki page for the VIC chip at http://sleepingelephant.com/denial/wiki ... nology_VIC
A man without talent or ambition is most easily pleased. Others set his path and he is content.
https://github.com/SvenMichaelKlose
Post Reply