60Hz demos?

[Hatta]

I was wanting to run some demos on my 1mb 520ST, but everything scrolls. Are there any good demos that are visible on an NTSC display?

[+rdemming]

As the ST demo scene was virtually non-existant in NTSC land the majority of demos came from PAL land. I personally don't know of any demo that was made for NTSC.

 

Demos that use special graphics tricks like sync scrolling, overscan or mid-line color chances will only work correctly on PAL.

 

Demos usually sync to the VBI to present smooth animation. That means there is 20 ms in PAL for processing a frame while on NTSC there is only 16.67 ms for processing a frame. Thus if the processing of a frame takes longer than 16.67 ms it will only work on PAL. In that case on NTSC the processing of the frame will not be finished before the next VBI which will cause problems.

If processing a frame takes less than 16.67 ms, then there might be a chance that it works on NTSC. However often demos set the refresh frequency explicitly on 50Hz causing the symptons you mention. And usually demos try to use every clock-cycle availble thus the changes a demo needs less than 16.67 ms per frame are small.

 

Thus to run a PAL demo successfully on NTSC the processing of a frame must take less than 16.67 ms, it must not use sync-scroll, overscan or mid-line graphics tricks and the demo must leave the 50/60 Hz frequency register alone (not put it back to 50 Hz).

 

I recommend that you connect your ST to an RGB monitor (like the Atari SC1224 or the Commodore 1084). These monitors support both 60 and 50 Hz and you should be able to run the demos correctly on an NTSC machine. However you might need to put your computer first in 50Hz for demos that don't do it themselfves. There are many programs out there that can do that but that only works if you don't have to reboot to load the demo disk.

 

Robert

[Hatta]

Rats. Guess I need to get my hands on some 13 pin DIN connectors then.

[Charlie_]

Most PAL demos run fine on a NTSC ST, but for some of them you have to run a 50Hz program before starting the demo.

For demos you are going to need a display capable of not rolling 50Hz, like an SC1224.

[+DarkLord]

I've only had a handful of demo scene type software that wouldn't work "out of the box"

on my SC1224. Occasionaly, as Rdemming and Official Ninja has mentioned, I've had

to use one of the boot utils that puts you in 50hz mode. Really not often though...