The A/T89C51AC2 is a high-performance Flash version of the 80C51 single-chip 8-bit microcontroller. It contains a 32 KB Flash memory block for program and data. The 32 KB Flash memory can be programmed either in parallel mode or in serial mode with ISP capability or with software. The programming voltage is internally generated from the standard VCC pin.

The A/T89C51AC2 retains all features of the 80C51 with 256 bytes of internal RAM, a 7-source 4-level interrupt controller, and three timer/counters. Additionally, it includes a 10-bit A/D converter, a 2 KB Boot Flash memory, 2 KB EEPROM for data, a Programmable Counter Array, an XRAM of 1024 bytes, a Hardware Watchdog Timer, and a more versatile serial channel that facilitates multiprocessor communication (EUART). The fully static design reduces system power consumption by bringing the clock frequency down to any value, even DC, without loss of data.

The A/T89C51AC2 has two software-selectable modes of reduced activity and an 8-bit clock prescaler for further reduction in power consumption. In the Idle mode, the CPU is frozen while the peripherals and the interrupt system continue to operate. In the Power-down mode, the RAM is saved, and all other functions are inoperative.

The added features of the A/T89C51AC2 make it more powerful for applications that need A/D conversion, pulse width modulation, high-speed I/O, and counting capabilities, such as industrial control, consumer goods, alarms, and motor control. While remaining fully compatible with the 80C52, the T8C51AC2 offers a superset of this standard microcontroller. In X2 mode, a maximum external clock rate of 20 MHz reaches a 300 ns cycle time.