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
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| 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]
- Press [⬅️], then [9]
You’re now in the maintenance menu, press [2] for OS Update functions. (Warning: you may accidentally delete your OS, be careful. Self-test or OS Update will cause a memory clear)
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| OS Update Process |
Notice the data transmission is scrambled. It's probably some early form of bitstuffing.
3. et cetera
Some photos
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