Reverse Engineering an Unknown Microcontroller #ReverseEngineering works on reverse-engineering eInk price tags. One particular company (Samsung Electro Mechanics/SoluM) switched from a third party chip (Marvell 88MZ100) to a new chip in their next generation tags. This chip seemed to be made by them, custom, for this purpose. This never bodes well for reverse-engineering. There were two types that had a segment-based e-Ink display and one that had a normal graphical eInk display. They had the same main chip on them, so I started with the segment-based device, since it is easier to understand a simpler unknown system.

Google image search helps in this project. It is an unexpected but very useful tool for reverse engineering sometimes.

The main MCU is revealed to be one ZBS242. Well, OK. That is not a microcontroller I am familiar with. Searching the internet some more finds us a link (archived here for posterity) that that StackExchange answer also mentioned. The page is in Korean, but it shows that this chip has an 8051 core, and a rather predictable set of peripherals: UART, SPI, I2C, ADC, DAC, Comparator, Temperature sensor, 5-channel PWM, 3-ch Triac controller, IR transmitter, Key scan functionality, RF-Wake, antenna diversity, and a ZigBee compatible radio and MAC. The image shows that it also has 32KHz internal RC oscillator and claims to be able to consume just 1 uA in sleep mode. I guess this is the company that made the chip for Samsung. Interesting…

Read the post for all the details used to find out about the chip, it’s capabilities, and more.

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