Thunder Castle Title Screen

[HunterZero]

While testing my PAL60 modified Intellivsion console, I plugged in Thunder Castle, and noticed that the title screen background is black when played on a 60Hz system. When the exact same cartridge is played on a 50Hz system, the background of the title screen is the standard olive green.

 

Wondered if someone here could give a technical explanation for why this is so?

 

It must be some sort of timing issue, as the only difference my PAL60 Intellivision has over a standard PAL one is the STIC chip, and the crystal.

 

- J

[+intvsteve]

Interesting... I can't recall off the top of my head if the color chip is different between the two (NTSC, PAL). Can't say I've ever fired up Thunder Castle on my PAL system. Now I'm curious!

[HunterZero]

Interesting... I can't recall off the top of my head if the color chip is different between the two (NTSC, PAL). Can't say I've ever fired up Thunder Castle on my PAL system. Now I'm curious!

 

The colour circuitry is different. US systems used a single chip solution, most PAL units have a daughterboard that generates the colour.

 

The colour circuitry in my PAL60 unit is the standard PAL circuit. I've seen screen caps of the game running on NTSC and the title screen is black. So the difference doesn't come from the colour circuitry.

 

So I am thinking it must be some code timing issue, as the only variables are the STIC and system clock. Perhaps the game programmer used some 'trick' with the EXEC that is timing sensitive to change the background colour on the title screen, and that trick doesn't work on PAL timed systems?

 

- J

Edited February 13, 2017 by HunterZero

[mr_me]

The MAME emulator does the same thing with Thunder Castle. It also does it with the Vectron titlescreen.

 

-Mattel's plan was to reduce the pal colour circuity to a chip. It's what held up the release of the Intellivision II in those markets. I'm not sure how the digiplay Intellivision II did it in Brasil.