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Hacking a CASIO fx-5800p Programmable Calculator

 Some information about the internals of fx-5800p, a cute programmable calculator that was very popular in the surveying market in China in the past. 1. SoC Dieshot SoC Markings: OKI ML610901B (CPU, RAM, Mask ROM, LCD Driver) Flash: 29LV800CBT (Only half of the Flash ROM is being used) RAM: 62256 Oscillator: Unknown, probably embedded. The oscillation frequency can deviate by quite a lot during serial communication. It's probably an RC or on-chip RC oscillator. 2. OS Update & Data Encoding “OS” refers to the binary data residing in the external Flash ROM. In fact, most of the core math, hardware access, communication, and maintenance functions are hard-wired inside the SOC (Mask-ROM). The font set and the power-off screen are also in the Mask-ROM. From what I know so far, the UI, statistics, and programming functions are probably in the external flash, which can be reprogrammed. To enter the OS Update menu: Shutdown the device using [SHIFT]+[AC/ON] Hold [MODE]+[7], Press [AC/ON

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