Intel 8031 microcontroller family
Intel 8031 and 80C31 are members of Intel MCS-51 family of 8-bit microcontrollers. 8031 / 80C31 have the same integrated peripherals as 8051 MCUs - 4 I/O ports, two 16-bit timers/counters, on-chip oscillator and a serial port. The MCUs have 128 bytes of internal RAM, and, in addition to that, can utilize up to 64 KB of external data memory. The microcontrollers don't have on-chip ROM, and must use external program memory.
Intel 80C31, CMOS version of the 8031 NMOS microcontroller, is fully pin- and object-code compatible with the 8031. The 80C31 offers lower power consumption than the 8031, and adds two low-power modes: