The AT89C1051U is a low-voltage, high-performance CMOS 8-bit microcomputer with 1K bytes of Flash programmable and erasable read only memory. It has the same functionality and operation as the AT89C1051 with the addition of a UART programmable serial port. 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 AT89C1051U is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The AT89C1051U provides the following standard features: 1K bytes of Flash, 64 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 AT89C1051U 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.