Asynchronous communication utilizes a transmitter, a receiver and a wire without coordination about the timing of just how long the transmiter leaves the signal at a certain level to represent a single digital bit. Each device uses a clock to mesure out the 'length' of a bit. The transmitting device simply transmits. The receiving device has to look at the incoming signal and figure out what it is receiving and coordinate and retime its clock to match the incoming signal.
Sending data encoded into your signal requires that the sender and receiver are both using the same enconding/decoding method, and know where to look in the signal to find data. Asynchronous systems do not send separate information to indicate the encoding or clocking information. The receiver must decide the clocking of the signal on it's own. This means that the receiver must decide where to look in the signal stream to find ones and zeroes, and decide for itself where each individual bit stops and starts. This information is not in the data in the signal sent from transmitting unit.
When the receiver of a signal carrying information has to derive how that signal is organized without consulting the transmitting device, it is called asynchronous communication. In short, the two ends do not synchronize the connection before communicating. Asynchronous communication is more efficient when there is low loss and low error rates over the transmission medium because data is not retransmitted. In addition, there is no time spent setting up the connection at the beginning of transmission--you just transmit and let the end station figure it out. One side simply transmits, and the other does it's best to receive.
EXAMPLES: Asynchronous communication is used on RS-232 based serial devices such as on an IBM-compatible computer's COM 1, 2, 3, 4 ports. Asynchronous Transfer Mode (ATM) also uses this means of communication. Your PS2 ports on your computer also use serial communication. This is the...
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