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Mystery Solved: Apple II MouseCard's VBL-Synced Interrupts

2025-05-08

This post delves into the synchronization mechanism between the Apple II MouseCard's IRQ interrupts and vertical blanking (VBL). The author initially observed flickering in MAME emulation but smooth rendering on real hardware. Through community interaction and analysis of the MouseCard firmware, the mystery was solved: the MouseCard doesn't directly receive the VBL signal but uses software on a 68705 microprocessor to precisely calculate and trigger interrupts, achieving VBL synchronization. This involves manipulating 6821 PIA registers and configuring the 68705's internal timer, ultimately achieving highly accurate VBL synchronization, consistent with Apple's official documentation.

Glider Returns: A Classic Apple II Game Reimagined

2025-03-27

The classic Apple II game, Glider, has been resurrected by a developer who painstakingly recreated it using 6502 assembly. Requiring an Apple ][+ or later model (mouse required on the ][+), this reimplementation offers both mouse and keyboard control and is best enjoyed on a monochrome display (by design). The developer has also shared a detailed development log detailing the journey of learning 6502 assembly and bringing the project to life. This free, playable version is a treat for retro gaming enthusiasts.

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