The AT89S53 is a low-power, high-performance CMOS 8-bit microcomputer with 12K bytes of downloadable Flash programmable and erasable read-only memory. The device is manufactured using high-density nonvolatile memory technology and is compatible with the industry-standard 80C51 instruction set and pinout. The on-chip downloadable Flash allows the program memory to be reprogrammed in-system through an SPI serial interface or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with downloadable Flash on a monolithic chip, the AT89S53 is a powerful microcomputer that provides a highly flexible and cost-effective solution to many embedded control applications.

The AT89S53 provides the following standard features: 12K bytes of downloadable Flash, 256 bytes of RAM, 32 I/O lines, a programmable watchdog timer, two Data Pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full-duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S53 is designed with static logic for operation down to zero frequency and supports two software-selectable power-saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset.

The downloadable Flash can change a single byte at a time and is accessible through the SPI serial interface. Holding RESET active forces the SPI bus into a serial programming interface and allows the program memory to be written to or read from unless Lock Bit 2 has been activated.