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sparkdrummer

VIC 20 Screen offset

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So I've been playing around with the VIC 20 I recently got. I have downloaded some games and transfered to real floppy.

Some of the games set up the screen lowered and to the right.

post-39776-0-23533800-1434276065_thumb.jpg

post-39776-0-37436900-1434276088_thumb.jpg

 

I am assuming this is happening because these games are PAL?

Is there any way to fix? The games look like they'd be fun to play.

p.s. - sorry about no color - that's the way my capture program interpreted it.

 

-Ralph...

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There's various registers on VIC that allow screen size and origin, so fixing as such should be possible.

And yes, entirely possible versions made for one TV system might look wrong on the other, and possible that there's already fixed versions for plenty of games already out there.

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The problem lies in that the 6560 VIC-I (NTSC) and 6561 VIC-I (PAL) have different value ranges.

 

Horizontal positioning: NTSC range 1-8, PAL range 5-19 (roughly)

Vertical positioning: NTSC range 5-130, PAL range 5-155 (roughly)

 

The PAL chip has a finer granularity in positioning the screen, and was also developed later on. Supposedly Commodore had trouble adapting the VIC-I chip to PAL, so the VIC-20 release was somewhat delayed in Europe, and may have caused a redesign with different value ranges.

 

If those games are in BASIC, you could look up any POKE 36864 (horizontal) and POKE 36865 (vertical) and try to change the values to lower numbers to move the screen to the upper left. If they're machine code, they're still possible to patch but a bit more complex.

 

For that matter, nearly every single VIC-20 cartridge, both those by Commodore and third party publishers, default to NTSC positioning. Some of those allow the user to reposition the screen with cursor keys or joystick, so PAL users also can enjoy cartridge games, but not all of them do. While working with the cartridge dumps for Mega-Cart, a number of games were patched on behalf of this, so a Mega-Cart ordered in PAL version would have much or all games centered for PAL use, while a cartridge ordered in NTSC version would be optimized for that.

 

Many inexperienced VIC-20 users believe those cartridges with screen offset in upper left position are exclusive US releases, and can keep searching until their fingers bleed for European releases of the same games, which never occurred as Commodore as well as the others thought it would be enough to include routines to reposition the screen.

 

For that matter, you can identify if your game runs on NTSC or PAL by reading values from the ROM, since the VIC-I chip is initialized with a set of numbers in ROM for screen position, number of columns and rows. Thus if those games had relied on that the Kernal routines would position the screen accordingly instead of doing it manually, the problem would never have occurred except for those games that reconfigure number of rows or columns. A few programs might actually check ROM and handle screen accordingly, but mostly newer homebrews.

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Yes, both games originated in the UK (by the looks of it, they are Firebird's Snake Byte and Imagine's Wacky Waiters) so the screen pointers will be for PAL displays. Yes, it is fixable, but you need to know where and what to POKE (which is outside my knowledge in general).

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Thanks guys

I kinda figured they were pal games. Fixing said games via pokes,etc is way beyond what this neophyte Vic user can do. Once I get my 16k expansion it's just gonna add to my confusion , right?

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I can't make any promises, but it might be possible that someone can help you patch the few PAL games you happen to find. Some of them use larger screen areas than usual - in particular Eugine Evans' games published by Imagine - and thus might not fit entirely on a NTSC screen even it is positioned properly.

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Ah well, they look like fun games but I'm still having some fun with my commodore stuff. It's definitely a change of pace from the ti world.

If somebody has hacked copies great, if not life goes on.

Ralph

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Attached is a ZIP file of Imagine games for the VIC20.

 

This includes Wacky Waiters NTSC version.

 

The archive has the following games in both PAL and NTSC format:

 

Arcadia

Bewitched

Catcha Snatcha

Frantic

Wacky Waiters

 

Note that these games requires memory at $A000 (Block 5) and are started with SYS64802, except Wacky Waiters which starts with SYS48896. I did not do the original dumps.

 

Also note Bewitched will crash if memory is present at address $2000.

 

I patched the NTSC versions using VICE, so let me know how they look on a real NTSC VIC.

 

Enjoy.

 

Graham

 

Imagine.zip

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Hey, thanks guys!

Sorry I'm so tardy in answering this thread.

I'm gonna download when I get near my computer and give em a spin.

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