116 Glossary

synchronous: Having a constant time interval between successive bits, characters or events. Synchronous data transmission requires both the sending and receiving devices to use special synchronizing characters to correct variations in timing between the devices. See also asynchronous.

T

Test function: When normal communication is not possible, this

function checks the modem, personal computer, and telephone

 

 

lines to determine if they are normal.

 

Tone dialing: A dialing method that uses tones instead of pulses to

 

generate a telephone number. Generally associated with push-

 

button phones, although some push-button phones can be

U

connected to pulse lines.

upload: To send a file to another computer through a modem. See

 

 

also download.

 

UART: Universal Asynchronous Receiver Transmitter is the circuit

 

interface between the modem and computer. It receives serial bit

 

data from the modem and converts it into bytes for the computer;

 

and it converts byte data from the computer into bit data for serial

 

communication.

X

XON/XOFF flow control: A protocol used by devices receiving

data. It uses two signals: transfer ON and transfer OFF. The

 

 

signals are controlled by software.