The ML63611A is a CMOS 4-bit microcontroller using Oki's original CPU core nX-4/250. The ML63611A is provided with the mask options of eight items of selection including (1.5 V or 3.0 V) power supply specifications and (With or Without) the regulator circuit for the LCD bias reference voltage. When a 3.0 V power supply specification is selected, the halver circuit can be used to decrease power consumption. The halver circuit cannot be used when a 1.5 V power supply specification is selected. When "With the regulator circuit for the LCD bias reference voltage" is selected, the LCD bias reference voltage will be generated based on the output voltage of the regulator circuit. When "Without the regulator circuit for the LCD bias reference voltage" is selected, the LCD bias reference voltage will be generated based on the power supply voltage; for this reason, the LCD bias voltage decreases as the power supply voltage decreases, causing the display density of the LCD panel to thin down. The ML63611A has incorporated in it an 8K-word program memory, a 1K-nibble data memory, four input ports, four output ports (only when the mask option of LCD driver pins is selected), 16 I/O ports, a melody circuit, a serial port, four 8-bit timers, and a 64-segment LCD driver (60 segment lines and 4 common lines, max.). (A part of the SEG pins can also be selected as output port pins or COM pins depending on the mask option.)