The AT8xC5111 is a high-performance ROM/OTP version of the 80C51 8-bit microcontroller in low pin count package. The AT8xC5111 retains all the features of the standard 80C51 with 4K Bytes ROM/OTP program memory, 256 bytes of internal RAM, an 8-source, 4-level interrupt system, an on-chip oscillator and two timer/counters. The AT8xC5111 is dedicated for analog interfacing applications. For this, it has a 10bit, 8 channels A/D converter and a five-channel Programmable Counter Array. In addition, the AT8xC5111 has a Hardware Watchdog Timer, a versatile serial channel that facilitates multiprocessor communication (EUART) with an independent baud rate generator, an SPI serial bus controller and a X2 speed improvement mechanism. The X2 feature permits keeping the same CPU power at an oscillator frequency divided by two. The prescaler allows to decrease CPU and peripherals clock frequency.