40 MHz 8-bit core for control-loop timing
The Microchip PIC18F2221-I/ML is an 8-bit MCU from the PIC® 18F family, clocked at 40 MHz. That 40 MHz core speed means single-cycle instruction execution at 10 MIPS — enough headroom for PID loops, UART polling at 115.2 kbaud, and sensor readout without a dedicated coprocessor. Program memory is 4 KB Flash (2K x 16), backed by 512 bytes RAM and 256 bytes EEPROM. For a firmware image that fits in 4 KB, this part is sized for a single-purpose control task — not a multi-stack RTOS. Supply range is 4.2 V to 5.5 V, so it runs cleanly on a 5 V rail common in industrial panels and automotive body modules. On-chip peripherals include Brown-out Detect/Reset, HLVD, POR, PWM, and WDT — enough to build a self-monitoring controller without external supervision. The 28-VQFN Exposed Pad package (6x6 mm) saves board area and the exposed pad helps thermal dissipation if the MCU drives external loads directly.