Modem stands for modulator demodulator . A modem changes the digital signal to an analogue frequency, and sends this tone across the analogue link. At the other end, another modem receives the signal and converts it back to digital. This is a standard modem with a micro-processor to provide both data communications and automatic dialing in the one unit. These modems offer a range of features, auto dial, the modem can seize the phone line and dial a number auto answer, the modem can answer an incoming call auto fallback, the modem can use a lower speed if the line is noisy accept commands, the modem can be reconfigured Modem Commands Modems can receive and act on commands from the computer terminal.
Commands begin with the symbol AT and are terminated with a carriage return.
The range of commands is called the AT Command Set. This is detailed in the reference listed above. The AT Command Set Hayes Corporation developed a smart modem that accepted AT type commands. This is now a widely accepted standard. The following is a brief list of the AT command set.