The STMicroelectronics STM32F091RCT6J is a 32-bit ARM Cortex-M0 microcontroller from the STM32F0 series, clocked at 48 MHz with 256 KB of Flash and 32 KB of RAM.
The 48 MHz core is the entry-level speed tier for the Cortex-M0 architecture. It handles sensor polling, Modbus RTU frames, and simple control loops without a problem, but it will not sustain heavy DSP or high-speed data logging. The 256 KB Flash is generous for this class — enough for a bootloader plus a moderate application image — while the 32 KB RAM keeps the bill of materials lean for designs that do not need external memory.
Where it fits — typical applications
The 52 I/O lines are available in the 64-LQFP package.