The AT89C4051 is a low-voltage, high-performance CMOS 8-bit microcomputer with 4K Bytes of Flash programmable and erasable read only memory (PEROM). The device is manufactured using Atmel's high density nonvolatile memory technology and is compatible with the industry standard MCS-51TM instruction set. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C4051 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The AT89C4051 provides the following standard features: 4K Bytes of Flash, 128 bytes of RAM, 15 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a full duplex serial port, a precision analog comparator, on-chip oscillator and clock circuitry. In addition, the AT89C4051 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 hardware reset.