8051 microcontrollers

8051 Data Communication Modes The 8051 has one serial port-port pins 3.0 (RXD) and 3.1 (TXD)-that receives and transmits data. All data is transmitted or received in two registers with one name: SBUF. Writing to SBUF results in data transmission; reading SBUF accesses received data. Transmission and reception can take place simultaneously, and the receiver can be in the process of receiving a byte while a previous byte is still in SBUF. The first byte must be read before the reception is complete, or the second byte will be lost. Physically the data is a series of voltage levels that are sampled, in the center of the bit period, at a frequency that is determined by the serial data mode and the program that controls that mode. All devices that wish to communicate must use the same voltage levels, mode, character code, and sampling frequency (baud rate). The wires that connect the ports must also have the same polarity so that the idle state, logic high, is seen by all ports. The i...

Introduction Chapter 2 contained an extensive review of serial data communication concepts and the hardware and software that is built into the 8051 for enabling serial data transfers. Chapter 7 contained some brief programming examples of how this capability may be used. Serial data transmission has become so important to the overall computing strategy of industrial and commercial applications that a separate chapter on this crucial subject is appropriate. One hallmark of contemporary computer systems is interconnectivity: the joining of computers via data networks that link the computers to each other and to shared resources, such as disk drives, printers, and other I/O devices. The beginning of the "computer age" saw isolated CPUs connected to their peripherals using manufacturer-specific data trans­mission configurations. One of the peripherals, however, was the teletype that had been borrowed from the telephone industry for use as a human interface to the computer, u...