20 MHz MSP430 core with USB — one chip for sensor fusion and host link
The MSP430F6635IPZ is a 16-bit MSP430 CPUXV2 microcontroller from the MSP430F6xx series, clocked at 20 MHz. It packs 256 KB of flash and 18 KB of RAM on a single die, with a USB 2.0 full-speed peripheral that handles device, host, or OTG roles — no separate USB controller chip needed on the board. The 100-LQFP package (14x14 mm) with 0.5 mm pitch is hand-solderable with a fine-tip iron — no hot-air or reflow required for prototypes. The 74 general-purpose I/O lines give plenty of headroom for parallel buses, keypad matrices, and status LEDs alongside the serial interfaces.
Peripheral set and memory — what fits on the BOM
On-chip peripherals include a 16-channel 12-bit ADC, brown-out detect, DMA, POR, PWM, and a watchdog timer. The 256 KB flash is generous for a mixed-signal MCU — enough for a USB stack, a real-time operating system, and application code without external memory. The 18 KB RAM is the tighter resource: budget it carefully if the application buffers large USB isochronous packets or multiple ADC scan buffers. Connectivity covers I²C, SPI, UART/USART, IrDA, LIN, and USB 2.0 — one chip handles the sensor cluster (I²C/SPI), the actuator bus (LIN), and the host link (USB) without external transceivers or protocol bridges. The internal oscillator keeps the BOM count low for applications that can tolerate ±1% accuracy; a crystal on the LFXT1 pins improves USB clock tolerance.