Serial communication is often used either to control or to receive data from an embedded microprocessor. Serial communication is a form of I/O in which the bits of a byte begin transferred appear one after the other in a timed sequence on a single wire. Serial communication has become the standard for intercomputer communication. 8051 provides a transmit channel and a receive channel of serial communication. The transmit data pin (TXD) is specified at P3.1, and the receive data pin (RXD) is at P3.0. The serial signals provided on these pins are TTL signal levels and must be boosted and inverted through a suitable converter to comply with RS232 standard.