High performance CMOS flash version of the 80C51 CMOS single-chip 8-bit microcontroller with a 64-KB flash memory block for code and for 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 of the features of the Atmel 80C52 and adds a programmable counter array, 1792 bytes of XRAM, hardware watchdog timer, SPI interface, keyboard, versatile serial channel that facilitates multiprocessor communication (EUART), and a speed improvement mechanism (X2 Mode).