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Author Topic: Need help removing demo mode from a ROM  (Read 1045 times)

spookgoblin

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Need help removing demo mode from a ROM
« on: November 07, 2017, 03:28:31 pm »
Hi there!

Does anyone know of a way to remove/turn off the demo mode (triggers from main menu and demos gameplay) from a ROM--specifically Castlevania 1?

Many thanks!

FAST6191

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Re: Need help removing demo mode from a ROM
« Reply #1 on: November 07, 2017, 04:45:31 pm »
Making an arcade type station?

Looking at http://datacrystal.romhacking.net/wiki/Castlevania:ROM_map and http://datacrystal.romhacking.net/wiki/Castlevania:RAM_map you are not likely to get an exact answer from them and will have to figure out something yourself.

It does mention a title screen routine so maybe keep that in mind for a first look.

Most such things just run off a timer, typically reset on a button press but might be something more specific instead. I see there is a timer of unknown use in the RAM map so the concept is clearly within the game somewhere, though it may be a different one here and it may still be a different method.

You would then want to look for a bit of timer related code (something which adds a number every frame, has another thing check it to see if it is above a certain value and then launch accordingly). As well as anything saying if greater than then play demo you may also have to change the addition code otherwise you could experience an overflow and whatever that might entail.


edale

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Re: Need help removing demo mode from a ROM
« Reply #3 on: November 07, 2017, 09:59:53 pm »
From that RAM map linked a few posts ago:

0x001E   Title Screen timer(time until attract mode)   Counts down from FF to 00.

I'd wager this is what you're looking for. I don't have the skills to tell you what to do with it though.


*edit-
I did verify that a cheat code of "001E:55" (I just chose a random number somewhere in the middle of the countdown, after watching that RAM Address' behavior for a while, and 55 was what I used) in FCEUX will completely eliminate the game entering the demo from the title screen, hitting Start still started the game as normal. You'd have to play the game for a while to see if this introduces any bugs.

If you can set your emulator up to load that cheat code with the ROM, then that may be your solution right there. A ROM hack solution would require more skills than I have.
« Last Edit: November 07, 2017, 10:17:46 pm by edale »