Texts 3-4

Text 3. Asynchronous Communication

Asynchronous communication is used for the transmission of non-time sensitive data. 

The term “asynchronous” means that the bits in the serial data stream are not locked to a specific clock that guides the timing of bits between the sending and receiving devices, as in “synchronous” communication. 

Instead, asynchronous communication relies on start and stop bits that bracket the characters. These bits are used to assist the receiving device in determining where each character in the data stream of ones and zeros begins and ends.   This makes the asynchronous method of serial data transmission ideal for terminal-to-host connections, where characters are generated at irregular intervals from a keyboard. 

Asynchronous communication is a simple, economical way to connect to a wide variety of systems and services, especially when the end device may be different with every connection attempt. This form of communication is commonly used for applications that are not real-time in nature, such as email or requesting Web pages. Any communication that is not time sensitive is considered asynchronous. Synchronous communication, on the other hand, is used for real-time applications. It relies on precise timing from a clock source, rather than start and stop bits, to make sense of the data stream.

                                    Text 4. Radio and television

Digital television standards and their adoption worldwide.

In a broadcast system, the central high-powered broadcast tower transmits a high-frequency electromagnetic wave to numerous low-powered receivers. The high-frequency wave sent by the tower is modulated with a signal containing visual or audio information. The receiver is then tuned so as to pick up the high-frequency wave and a demodulator is used to retrieve the signal containing the visual or audio information. The broadcast signal can be either analog (signal is varied continuously with respect to the information) or digital (information is encoded as a set of discrete values). 

The broadcast media industry is at a critical turning point in its development, with many countries moving from analog to digital broadcasts. This move is made possible by the production of cheaper, faster and more capable integrated circuits. The chief advantage of digital broadcasts is that they prevent a number of complaints common to traditional analog broadcasts.

 

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