Author Topic: Door Door discovery  (Read 78 times)

forgotusername

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Door Door discovery
« on: October 12, 2019, 02:25:09 AM »
While doing some hacking stuff recently out of boredom, I noticed something strange about the game Door Door. As common as it is on bootleg multicarts, every knockoff version of it is...weirdly altered. Most notably, the doors can be opened multiple times after letting an enemy inside; in the original game, they can only be opened once. Additionally, the life counter doesn't appear, and the score resets to zero upon entering a new level. Check any multicart with the game; they ALL do this!

So I decided to put an unaltered Door Door ROM into a multicart menu. At some point in the gameplay, the graphics will completely glitch out, usually after closing a door or touching the candy. For whatever reason, bootleg carts can't handle running the game normally... (I actually have a plug & play that has this glitch in it [Super Joy III variant], so I know its not an emulation error. It always pissed me off as a kid)

My question is: is Door Door just something the crappy multigames cannot handle properly? Or is this a very early form of copy protection, from the developers seeing the possibility of pirates appearing in the future? Is it able to detect if the ROM is above a certain filesize or something, and intentionally breaks the game from there?

Picture attached of glitch results when importing the original version over the bootleg in a multicart.

NewRisingSun

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Re: Door Door discovery
« Reply #1 on: October 12, 2019, 01:56:46 PM »
The game occasionally writes to the CPU $8000-$FFFF range. This has no effect on the original NROM cartridge, but on OneBus and other multicarts, it will be interpreted as a mapper write. That has the effect of causing glitches in the graphics.
« Last Edit: October 12, 2019, 01:58:40 PM by NewRisingSun »