![]() This would include things like player movement, enemy AI, player shots and bullets etc. So in a game like Galaxian, there are two contexts of code execution the 60Hz VBLANK interrupt, which is wired to the Z80's NMI and causes the CPU to execute code at address 0066h, and the main code which starts executing at address 0000h when the CPU is reset and runs (continues) after the aforementioned NMI handler routine is finished until it fires again.Īside from various hardware functions, the NMI handler contains all the processing in the game that affects, and is affected by, the speed that the game is running. ![]() Not only does this allow the game to update the sprites without any flicker or tear, it also serves as a reliable, periodic timer on which to base the speed of the game. Before we can create a framework for the transcoded game, we need to understand the architecture of the original.Įvery single arcade game that I have reverse-engineered thus far has been driven by the 60Hz VBLANK interrupt.
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