AT80C51RD2-SLSUM 8-bit MCS-8051 microcontroller, ROMless, 40 MHz, PLCC-44

AT80C51RD2 microcontrollers are high-performance versions of the 80C51 8-bit microcontrollers. They retain all functions of the Atmel 80C52 - with 256 bytes of internal RAM, an interrupt controller with 7 sources and 4 levels and three timers/counters. The microcontrollers also feature a programmable counter array, 1024-byte XRAM, a hardware watchdog timer, keyboard interface, a more versatile serial channel that facilitates multiprocessor communication (EUART) and a speed-improvement mechanism (X2 mode). The microcontrollers are equipped with two software-selectable modes for reduced activity as well as an 8-bit clock prescaler to further reduce power consumption. In idle mode, the CPU is frozen while the peripherals and interrupt system are still in operation. In power-down mode, the RAM is saved and all other functions are disabled.