The W78L801 is an 8-bit microcontroller which can accommodate a wide range of supply voltages with low power consumption. The instruction set for the W78L801 is fully compatible with the standard 8051. The W78L801 contains an 4K bytes Mask ROM; a 256 bytes RAM; four 8-bit bi-directional and bit-addressable I/O ports; an additional 6-bit I/O port P4; two 16-bit timer/counters; a hardware watchdog timer. These peripherals are supported by a twelve sources two-level interrupt capability. The W78L801 does not contain serial port. The W78L801 microcontroller has two power reduction modes, idle mode and power-down mode, both of which are software selectable. The idle mode turns off the processor clock but allows for continued peripheral operation. The power-down mode stops the crystal oscillator for minimum power consumption. The external clock can be stopped at any time and in any state without affecting the processor.