SN8P22421 is designed with the excellent IC structure including the program memory
up to 3K-word OTP ROM, data memory of 128-bytes RAM, one 8-bit basic timer (T0), a
watchdog timer, four interrupt sources (T0, USB, Wakeup, INT0). There are two oscillator
configurations to select for generating system clock, including High/Low Speed crystal
or cost-saving RC. This device also includes an internal RC oscillator for slow mode
controlled by programming.