GENERAL DESCRIPTION
The OKI MSM80C31F/MSM80C51F microcontroller is a low-power, 8-bit device implemented
in OKIs silicon-gate complementary metal-oxide semiconductor process technology.  The
device includes 4K bytes of mask programmable ROM (MSM80C51F only), 128 bytes of
data RAM, 32 I/O lines, two 16-bit timer/counters, a five-source two-level interrupt
structure, a full duplex serial port, and an oscillator and clock circuitry.  In addition, the device
has two software selectable modes for further power reduction — Idle and Power Down.  Idle
mode freezes the CPUs in-struction execution while maintaining RAM and allowing the timers,
serial port and interrupt system to continue functions.  Power Down mode saves the RAM
contents but freezes the oscillator causing all other device functions to be inoperative.