The document discusses the UART receiver. It begins by introducing UART and describing its basic functions of serial communication and ability to receive and transmit data. It then details the components of a UART including a baud rate clock generator, input/output shift registers, transmit/receive control logic, buffers and optional FIFO. The document goes on to describe the data framing process used in UART including start bits, data bits, parity bits, and stop bits. It explains how asynchronous transmission works without a clock signal and how the receiver synchronizes. The document provides low-level details about how the UART receiver operates on a bit-by-bit level to receive serial data and convert it to parallel format.