This web content dives into the unexpected discovery of a coding error in the ROM of the Macintosh Classic II that led to a crash being averted. Through detailed analysis using MAME emulator and disassemblers, the author unravels the mystery behind a CAS instruction that magically corrects an invalid address in the CPU, preventing a Sad Mac error. The surprising twist is that this glitch in the ROM code seems to have been inadvertently compensated for by the CPU, explaining why the issue was never noticed on actual hardware. The article offers a deep dive into the technical intricacies of vintage Apple technology, showcasing the intricacies of troubleshooting and emulation.
https://www.downtowndougbrown.com/2025/01/the-invalid-68030-instruction-that-accidentally-allowed-the-mac-classic-ii-to-successfully-boot-up/