Data Communications Networking Devices - 4th Ed.pdf

4.3 INTELLIGENT MODEMS ________________________________________________________ 433Table 4.21CommandBasic Hayes command set major commands)DescriptionATAttentionAAnswer callA/ Repeat last commandBSelect the method of modem modulationC Turn modem's carrier on or offDDial a telephone numberEEnable or inhibit echo of characters to the screenF Switch between half- and full-duplex modem operationHHang up telephone on hook) or pick up telephone off hook)IRequest identi®cation code or request check sumLSelect the speaker volumeMTurn speaker off or onOPlace modem on-linePPulse dialQRequest modem to send or inhibit sending of result codeR Change modem mode to 'originate-only'SSet modem register valuesTTouch-tone dialVSend result codes as digits or wordsXUse basic or extended result code setYEnable or inhibit long space disconnectZReset the modem+ + + Escape commandCommands followed by an asterisk ) are not applicable to the Hayes V-series Smartmodem2400 but are recognized by earlier Hayes modems and modems manufactured by many othervendors.many commands do not have parameters, those terms are enclosed in bracketsto illustrate that they are optional. A number of commands can be included inone command line as long as the number of characters does not exceed 40, which isthe size of the modem's command buffer. Finally, each command line must beterminated by a carriage return character.Command useTo illustrate the utilization of the Hayes command set let us assume we desire toautomatically dial New York City information. First, we must tell the modem to gooff-hook, which is similar to one manually picking up the telephone handset. Thenwe must tell the modem the type of telephone system we are using, pulse or touchtone,and the telephone number to dial. Thus, if we have a terminal or personalcomputer connected to a Hayes compatible modem, we would send the followingcommands to the modem:AT H1AT DT1,212-555-1212In the ®rst command, the 1 parameter used with the H command places themodem off-hook. In the second command, DT tells the modem to dial D) a