14,400 Modem & Fax (250-3036) Operation Faxback Doc. # 3251 DIALING & ANSWERING WITH THE AT COMMAND SET This chapter describes the modem's command and communications modes and the guidelines you need to follow to manually give the modem commands. To send commands to the modem, you must be running a communications program. SWITCHING FROM THE COMMUNICATIONS TO THE COMMAND MODE Escape Code The escape code is a code you send to the modem to make it switch from the command mode. When you switch modes, the modem does not disconnect from the phone line. It merely suspends the transfer of information. The default escape code sequence is: Wait at least 1 second without typing a character. Type:+++ Wait at least 1 second for the modem to acknowledge. The modem acknowledges by sending OK (or 0 if you turn off word request codes). The reason for the 1 second wait before and after sending the escape code is to prevent accidentally switching modes. If you type anything within 1 second (the escape code guard time) of escape code, the modem ignores the escape code. You can change the default values of the escape code and the escape code guard time. The escape code is a single character you enter three times, surrounded by a designated period of time. Refer to "Internal Modem Registers," Registers S2 and S12, to change the default values. COMMAND SYNTAX This section describes the various elements that make up all modem commands. Attention All commands must begin with the letters AT. AT is short for "ATTENTION" and the modem uses these letters to automatically set the speed and the parity. You can enter AT and all other commands in either upper or lower case. Line Length Limits You can type one or more commands after the AT. The modem performs the commands in the order given. The number of commands you can give at one time is limited by the line length, which cannot exceed 42 characters. The modem does not count control characters and spaces, but it does count punctuation marks such as dashes or commas. Carriage Return ENTER denotes a carriage return. This ends the command; the modem does not process the command until it sees the ENTER. Line Editing After you enter a command (before you press ENTER), you can edit the command using the backspace key, which deletes the last character you entered. NOTE: If you backspace over a space, the modem ignores the space and erases the next character. In this case, the computer does not display the command properly. Parameters Most commands consist of a single letter followed by a single-digit parameter, or option. If you do not follow the command with a parameter, the modem assumes a parameter of 0. Repeat (A/) Repeats the command line. Neither AT nor ENTER is necessary with this command. Example Command The following are two examples of valid modem commands. AT X4 V1 DT (408) 555-3438 ENTER ATXVDT4085553438 ENTER Note that you do not need to enter any spaces. But spaces make the command easier to read (although, usually harder to edit). DIALING COMMAND AND OPTIONS This section describes the dialing command and its options. Dial Command (D) D is the dial command. You can enter several other associated commands as part of a dial command. In its simplest form, follow the dial command with the number you want the modem to dial. AT D 555-8900 ENTER NOTE: The modem ignores the spaces and the dash (-). The modem dials the number and waits 30 seconds (default) for a response from the called modem. If the other modem answers, the modem sends the CONNECT, CONNECT 1200, or CONNECT 2400 result code, depending on the other modem's speed. The modem then enters the communication mode and begins communicating with the other system. If the modem does not hear another modem, it returns a NO CARRIER or BUSY result code. Pause (,) A comma in the dial sequence tells the modem to pause two seconds, then continue. You might want to use this if you dial from a system where you have to access an outside line, then dial the outside number. ATD 9, 555-8912 ENTER Dial 9, pause for 2 seconds, then dial 555-8912. NOTE: You can use more than one comma to increase the pause time, or change the time by setting Register S8. Wait for Dial Tone (W) A W in the dial sequence tells the modem to wait for a dial tone. You could use this if you use an alternate long-distance carrier, or if you dial from a system that requires an access code for a long-distance number: ATD23W555-1893 ENTER Dial 23, wait for a dial tone, dial 555-1893. The X command and the contents of Register S7 determine how long the modem waits for the dial tone. If you set X2 or X4, the modem waits for 5 seconds. Otherwise, the modem waits for the time set by Register S7. If the modem does not hear a dial tone within the specified time, it returns NO DIALTONE. Wait for Silence (@) An @ in the dial sequence causes the modem to wait for 5 seconds of silence after one or more rings. You could use this if you dial a long-distance service that does not produce a second dial tone. The modem waits the length of time specified in Register S7 (default 30 seconds) for the 5 seconds of silence. If the modem does not detect silence, it returns the NO ANSWER or BUSY result code. ATDT 555-2323@23 ENTER Dial 555-3439, wait for silence, dial 23. Switch hook Flash (!) An ! causes the modem to perform a flash. This makes the modem hang-up the phone line for about 0.5 second (like pressing and releasing the switch hook on the telephone). Some phone systems use this function to transfer calls. ATDT555-3439! ENTER Dial 555-3439, flash. Touch Tone Dialing (T) Pulse Dialing (P) The T and P dial modifiers select the dialing method the modem uses. The modem defaults to using pulse dialing. You could use this to use alternate long-distance services from a pulse dial line. ATD9WT 555-2322 ENTER Dial 9 pulse mode, wait for a dial tone dial 555-2322 in tone mode. The modem dials using the last method used, so, in the above example, any additional dial commands use touch tone unless you specify pulse. Memory Dial Number (S=n) S=n (where n is 0-3) in the dial sequence makes the modem dial one of four telephone numbers you previously stored using the &Zn command. ATDS=1 ENTER Dial the number stored in redial memory 1. Return to Command Mode (;) A ; in the dial sequence tells the modem to return to the command mode as soon as it finishes dialing. The modem does not try to detect a carrier. You would use this command when you use the modem to dial a voice call. ATD 555-8373; ENTER Dial 555-8373. Auto-Dialing Voice Calls You can have the modem dial any telephone number, even if a computer is not connected to the other phone. Lift the telephone handset, send the dialing command, and listen for the other party to answer. At any time after the dialing stops, you can press any key to disconnect the modem. ATDT 555-1281; ENTER Dial 555-1281. When the person answers, press any key to disconnect the modem. Dialing Timing Parameters Registers S6 through S11 control the timing of the dialing commands. Refer to "Internal Modem Registers" for complete information about these registers. AUTO ANSWER OPERATION You can set the modem to automatically answer calls. This can be a useful feature if you need to access the computer from another computer. As set at the factory, the modem does not automatically answer incoming calls. You control the auto answer feature using Register S0 which determines the number of rings before the modem answers. If you set the register to 0 (default) the modem does not automatically answer the phone. Otherwise, the modem waits for the number of rings you specify (1-255). AT S0=1 ENTER The modem answers after one ring. AT S0=5 ENTER The modem answers after five rings. AT S0=23 ENTER The modem answers after 23 rings. After the modem answers, it sends an answer tone and waits for an originate tone. If the modem hears an originate tone, it returns the appropriate CONNECT result code to the computer. If the modem does not detect the carrier within 30 seconds after answering, it returns a NO CARRIER result code, hangs up, and returns to the command state. If the telephone rings when auto answer is disabled, the modem returns a RING result code and does not answer. You can use the Immediate Answer command (A) to have the modem pick up the phone line. IMMEDIATE ANSWER (A) You can force the modem to pick up the phone line, even if the phone does not ring. You might use this feature if you called someone on a voice line, then wanted to switch to communicate with their computer or if the telephone rings, and you want the modem to answer. If you are switching from a voice call to a data call, the other party must send AT D ENTER to their modem. AT A ENTER The modem immediately picks up the phone line and sends an answer tone. Auto Answer Timing Parameters Register S0, S7, and S9 control the answer mode timing. For more information on register settings, refer to "Advanced Programming Commands". Common Configuration Setup Strings (For class II Fax Modem only) 1. Force V.42bis data compression with LAP-M error correction AT\N4%C2 2. Force V.42bis data compression with MNP error correction. AT\N5%C2 3. Force MNP 5 data compression with MNP error correction. ATn5%C1 NOTE: With the setup strings in examples 1-3, if the remote is unable to negotiate the desired rate mode, the modem will disconnect and respond with No carrier. 4. Auto negotiate data compression and error correction. AT&F (factory defaults) or AT\N3%C3 In this mode, the mode prefers V.42bis over MNP. If error correction is not negotiated, the modem will connect in normal mode. (br/all-10/17/94)