 This is the world's first microcontroller which incorporates IEBus controller.Its IEBus controller function is almost the same as that of µPD72042B, but is located as memory mapped I/O called SFR (special function registers).6.291 MHz base clock is generated from 6.291 MHz external resonator, while host CPU core and watch timer works 8.388 MHz generated from the same external resonator.