The  microcontrollers described in this data sheet are high-performance static 80C51 designs incorporating Philips’ high-density CMOS technology with operation from 2.7 V to 5.5 V.
8xC31X2/51X2 and 8xC32X2/52X2/54X2/58X2 contain 128 byte RAM and 256 byte RAM respectively, 32 I/O lines, three 16-bit counter/timers, a six-source, four-priority level nested interrup structure, a serial I/O port for either multi-processor communications, I/O expansion or full duplex UART, and on-chip
oscillator and clock circuits.