Question(s) about Vic 20 PAL tape games

[gyuuu]

Noob question, hoping I can pick someone's brain here.

 

I recently got a Vic and I'm quite interested in games on cassette from the UK. I bought a handful of tapes and booted them up and they play just fine, but two of them (Arcadia and Crazy Cavey) are off-center on my NTSC machine. I know this is because they were developed for PAL machines, and I'm wondering if there are any simple solutions to get this displaying properly without having to identify and poke the screen values for each game.

 

I've been using the Vic through composite on an LCD TV and haven't tried it on a CRT yet, would this possibly make any difference? Or alternatively would one of those cheap Chinese NTSC to PAL converters potentially fix the issue?

[carlsson]

Nope. The only way you can solve this is to get a PAL VIC-20, or hack the program.

 

The problem consists of that the NTSC 6560 chip and the PAL 6561 chip use different value ranges for screen positioning. It means the values used to center the screen on NTSC would put it at the upper left corner on PAL, and vice versa a game hard coded to be centered on PAL would display in the lower right corner on NTSC, or perhaps be outside of visual area.

 

The Kernel chip in the computer exists in PAL and NTSC versions and contain the default values for respective graphics chip. However instead of reading those ROM values, many games hard code their screen positioning themselves which causes this problem. Most commonly it is seen with cartridges intended for the US market, which then make the screen appear in the upper left corner in Europe. Some of those games, mostly Commodore's own, have solved it by letting the user move the screen with cursor keys or joystick but far from all developers thought about it. To make matters worse, the majority of games use the default screen of 22 columns x 23 rows which means the system will automatically position the screen correctly before the game relocates the screen to what it thinks are the proper coordinates. Thus if the developer had not bothered to position the screen at all, the problem would never have occurred.

 

Trying to modify the video signal from the computer thus won't solve anything, since it is a software issue. If you would be getting a PAL VIC-20, you might though need a PAL to NTSC converter in case your gear can't display the PAL signal (preferrably in colour) but that is something else than the screen is off center.

 

If the mentioned games don't rely on any raster timing tricks and just change the screen layout, they may be possible to hack, either by hard coding new values into them or inserting a routine that works with relative offsets to the ROM defaults. Actually the program might read the ROM values and use that as an indicator if the game is run on PAL or NTSC and adjust the screen positioning based on that, since it is not thought that any NTSC user will have a PAL Kernel or vice versa, that would position the screen off center all the time.

 

A handful of games existed in separate PAL and NTSC versions, but those would usually be games waiting for the raster beam which requires them to be reprogrammed. For this reason, some of the games from Commodore (e.g. Bandits) only work on NTSC by the way. I can't recall seeing any PAL hacked versions of those few games.

[gyuuu]

Thanks for the info carlsson, appreciate you being willing to spell the issue out for someone uneducated on this stuff like myself

 

Sounds like I'm just gonna need to test games out on an emulator before going and buying tapes - thankfully most of the games I bought work just fine. I'm curious if there's any sort of documentation anywhere detailing which games were programmed solely for PAL, a lot of really interesting Vic games seem to have only been released in Europe on tape. I suppose I could just to the SD2IEC route and not have to worry about it but I really like having the physical media.

[carlsson]

It was worth my time to be verbose, since there tends to be some misunderstanding on things like this. While there are lists of all known VIC-20 tapes, I'm not sure if they specify which ones were exclusive to Europe. What you could do is to download files and perhaps get help to hack them, but also buying the original tapes of the games you like, even if you really can't load the tapes.

 

I seem to recall there are small differences in clock frequency between PAL and NTSC. Perhaps on the VIC-20 the difference is so small that normally tapes will load in either direction.

[gyuuu]

Yeah I grabbed 7 tapes and 5 of them loaded and played just fine, they maybe played a little faster than intended but not to the point of being unplayable. The ones that worked were antimatter splatter, rockman, space snake, R.I.P. the game and multitron; no issues with any of those.