A decap of the MCU reveals that it is from Renesas and is likely a R5F51135ADLJ (128KB ROM flash, 32KB RAM, 8KB data flash). This is based on Renesas’ proprietary RX CPU architecture which is a big change from the last generation of Bayer BGM which used an STM32F103 ARM-based MCU. Someone did a complete code rewrite to port the code over from the ARM code of the last generation.
Given that the peripheral set, performance and power consumption of the 2 MCUs are not massively different, there must have been a compelling price reason for doing so. Alternatively, perhaps enough of the code needed to be rewritten to support real-time Bluetooth comms for the first time that it was worth revisiting the whole code set?
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