HC08 core at 6 MHz with 48 KB on-chip Flash
The MC68HC908BD48I: The 48 KB on-chip Flash (48K x 8) gives firmware headroom for USB stack + application code without external memory — the 1 KB SRAM buffers USB transactions and I²C data streams, but tightens the runtime heap for multi-buffer operations.
USB and I²C connectivity in a through-hole package
This MCU integrates USB and I²C interfaces — the USB peripheral handles full-speed device-class communication, while the I²C bus connects to sensors, EEPROMs, or display controllers. The 42-pin SDIP (0.600-inch row spacing, 15.24 mm) and PDIP packages are through-hole, so the board assembly uses wave solder or hand-solder — no reflow profile needed, but the larger footprint limits board density compared to a QFP or QFN. Thirty-two general-purpose I/O pins handle external peripherals and control signals. Six-channel 8-bit ADC reads analog inputs like potentiometers or temperature sensors.
Peripherals: POR and PWM for power-on and motor control
On-chip peripherals include Power-On Reset (POR) and Pulse-Width Modulation (PWM). POR eliminates an external reset supervisor IC if the supply ramp meets the POR threshold timing. The PWM module drives DC motors, LED dimming, or class-D audio — the 6 MHz core clock limits the PWM carrier frequency to about 23 kHz at 8-bit resolution (256 counts), which is audible but usable for motor speed control.