Sunday, April 12, 2009


Computers cannot work directly on your telephone line. The digital information processed by computers must be translated into audible sounds that are carried across telephone lines to a remote location. The sound signals coming from the telephone lines must be converted back into digital information for the computer. A device called Modulator/Demodulator (MODEM) performs this continuous process of modulation and demodulation between a computer and telephone line. As the number of personal computers has grown into millions, the demand for faster and more reliable modern communication has resulted in impressive speed and performance. Today’s modems have also enabled entirely new developments such as facsimile and voice-over-data capabilities. Most modems today can be fabricated with only a few specialized chips and discrete parts, and virtually all computer communication systems contain the same essential parts. First, data must be translated from parallel into serial form and back again. Serial data being transmitted must be converted into an audio signal, and then placed on ordinary telephone circuit. Audio signals received from the telephone line must be separated from transmitted signals, and then converted back into serial data. All of these activities must takes place under the direction of a controller circuit. Finally, a modem uses nonvolatile RAM (NVRAM) to maintain a lengthy list of setup parameters.

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