High-performance CMOS flash version of the 80C51 CMOS, single-chip, 8-bit microcontroller with a 64KB flash memory block for program and data. The flash memory can be programmed in parallel or serial mode using ISP or software. The programming voltage is internally generated from the standard VCC pin. This device retains all features of the Atmel 80C52 and adds a programmable counter array, 1792 byte XRAM, a hardware watchdog timer, SPI and keyboard, a more versatile serial channel that facilitates multiprocessor communication (EUART), and a speed improvement mechanism (X2 mode). A fully static design reduces system power consumption by bringing the clock frequency down to any value without data loss. Two software-selectable modes of reduced activity and an 8-bit clock prescaler further reduce power consumption.