Software Vault: The Gold Collection

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SPORTSTER 14,400 CHAPTER 6. DIALING AND ANSWERING BEFORE CONNECTING For two modems to connect and exchange data, they must use the same modulation standard and, for error control to be successful, the same error-control protocol. Modulation/Standards The Sportster 14,400 modem conforms to the following modulation and signaling standards. CCITT V.32 bis 14.4K/12K/9600/7200/4800 bps CCITT V.32 9600/4800 bps CCITT V.22 bis 2400 bps Bell 212A/ CCITT V.22 1200 bps CCITT V.23 1200 bps with 75-bps back channel (sometimes used in U.K. and Europe) CCITT V.25 Answer sequence for calls originating outside the U.S. and Canada Bell 103/ CCITT V.21 300 bps CCITT V.42 LAPM error control, 1200 bps and above CCITT V.42 bis Data compression, 1200 bps and above MNP Levels 2, 3 and 4 error control, level 5 data compression, 1200 bps and above CCITT V.54 Analog, digital and remote digital loopback testing Setting the Transmission Rate Setting your software to 38.4K or 19.2K bps ensures that the Sportster 14,400 can operate at its highest rate. The modem detects the rate from the AT command, operates at that rate at the serial port, and tries to connect with remote modems at 14.4K bps, its highest connection rate. Follow the guidelines in Chapter 3, Quick Start, or the more detailed instructions in Chapter 4 before selecting either variable or fixed serial port rates (&Bn). If your software supports a fixed serial port rate, set the modem to &B1 and your soft ware to a high serial port rate for the best throughput. Set the modem for flow control (&Hn), as well. We recommend leaving the modem at its link operation factory setting, &N0, unless your application requires that you specify a fixed connection rate. &N0 allows the Sportster 14,400 to auto matically negotiate with the remote modem for the highest possible connection rate. Data Format Both your machine and the remote computer must use the same 10-bit data format, which always consists of 1 Start bit, plus one of the 9-bit combinations listed in Table 6.1. You may have to phone the remote computer installation or BBS to find out what word length, parity and Stop bit combination is required. Before calling, set your communications software (or terminal if you are using one) to the required scheme. Some commu nications programs use a kind of shorthand for formats, such as 7-E-1 or 8-N-1. The modem detects the format from the AT prefix of the next command it receives from your keyboard or from your software. Table 6.1_Allowable Data Formats Word Parity Stop Length (1 Bit) Bits 7 Even, Odd, 1 Mark, Space 7 None 2 8 None 1 Error Control For reliable high-speed data transfer, always set the Sportster for error control, &M4 (default) or &M5, for calls at speeds over 2400 bps. Most users communicating with V.42- or MNP- compatible modems will want error control at 2400 and 1200 bps, as well. The &M command is described in Chapter 4. If you're dialing out, it's a good idea to find out if the remote modem is MNP- compatible. Some public network services, for example, are not. If the remote modem doesn't have MNP capa bility, it may misinterpret the MNP error-control request and block a successful connection. If you know the remote modem doesn't support MNP, dis able MNP handshaking by setting Register S27 to 16 (ATS27=16). The modem still connects with V.42-compatible modems and modems that do not perform error control. To reset the modem for normal opera tions, issue the ATZ (reset) command, or set Register S27 to zero. PLACING CALLS This section discusses commands used in the following operations. Dialing D (0-9 # * , / ; " ! P T W @ R), DS Redialing A/ Canceling dialing<any key> Dial (D) The following command example instructs the modem to stop the display of commands (E0, turn off the local echo), turn off the speaker (M0), and dial (D) the phone number (1234567) using Touch- Tone dialing (T). The spaces shown are ignored by the modem and are only included here for readability. AT E0 M0 DT 1234567 <Enter> When the Dial command is issued, the modem goes off hook_ the equivalent of picking up your phone_then enters Originate mode and dials the number sequence that follows. The modem also executes any other commands or options included in the command line. The dial string may include up to 40 characters. The modem counts but ignores punctuation characters such as parentheses and hyphens. It does not count spaces, the AT prefix or the carriage return (Enter key) required to execute the command. Cancel Dialing To cancel Dial-command execution, press <any key>. If you inadvertently hit a key on the keyboard while the modem is dialing, the call is canceled. If this occurs, type the A/ command (explained under Redialing later in this chapter). On receipt of A/, the modem redials. Dial Command Options You may want to review the many options on the next several pages that are available for tailoring Dial strings. The most typically used are the Dial Type, Pulse or Tone, and the Pause options_comma, slash and W. Dialing Type, Pulse or Tone The modem is shipped to default to pulse (rotary) dialing. To have the modem use tone dialing, which includes the asterisk (*) and pound sign (#), use the T command. Dialing type commands may be included in the Dial string (ATDT number), issued separately (ATT or ATP), or included in the &W default configuration string you write to NVRAM, as explained in Chapter 5. You can also set the X2, X3 or X4 result code options, which include adaptive dialing, explained next. NOTE: You can switch from one dial type to another within a dialing sequence. Keep in mind that the modem remains set to the last dialing type instruction until it is reset (ATZ command) or it receives a different dial-type command. Adaptive Dialing (X2OX4) When any of the X2 through X4 options is in effect and you do not issue a dialing type in the Dial string, the Sportster 14,400 uses tone dialing, which is faster than the default pulse type. How ever, if the phone company's central office does not have Touch-Tone detection equipment, the modem cannot break dial and continues to detect the dial tone. If this occurs, the modem automatically reverts to pulse dialing. Pause (,) A comma causes a two-second delay in the dial sequence. The following example contains four-second delays at several points. ATDP 9,,7654321,,55555,,1 312 1234567 <Enter> The first four-second pause is to access an outside line after dialing 9, but you may wish to use the W option, described below. The second pause is to make sure the remote system is ready for the user's account number, and the third, to delay before dialing the long-distance number. Such pauses, however, may not be necessary. Experiment and use delays only as required. Slash (/) A slash (/) can be used in any command string to make the modem pause for only 125 milliseconds. Some users find it helpful to have the shorter delay of a series of slashes, rather than the 2- second comma pause. Wait for Another Dial Tone (W) This command is useful in situations where you must wait for a second dial tone before continuing dialing. For example, if you need to dial for an outside line, as in the following exam ple, the Sportster 14,400 continues dialing as soon as it detects the next dial tone. ATD9W1234567 <Enter> NOTE: This command executes only if result code option X3 or greater has been issued. If the modem is set to X2 or lower, the modem interprets the W as a comma (two-second pause). Dial and Return to Command Mode (;) If your phone is plugged into the modem, you can use this option to have the modem Auto Dial a telephone rather than a modem. The Sportster 14,400 dials, remains off hook and returns the OK message, indicating it is in Command mode. For example, to have the modem place a voice call, enter the Dial command with a semicolon. ATDT5551234; <Enter> When the modem returns the OK result, pick up your phone receiver so you can talk to the other party, and send the command that hangs up the modem. ATH <Enter> Similarly, you can call a recorded weather or other service. Have the modem Dial, listen to the recording over the modem's speaker and, when you are finished, instruct the modem to hang up. Dialing Letters (I) Quotation marks are used to make the modem dial abbreviations and acronyms used as phone numbers, such as DIAL USR (the USRobotics Sales Department's 800 number). The option is called Quote mode. Quotation marks are inserted at the beginning of the alphabetic string. ATDTIBBS NEWS <Enter> NOTE: If you are including another command after the dial string, use closing quotation marks before the additional command. Transferring Calls (!) This command applies to modems in installations where other modems share the phone line. The modem flashes the switch-hook, that is, it goes off hook 0.5 seconds, on hook for 0.5 seconds, and off hook again to dial the specified extension. The following example includes instructions to return to Com mand mode (;) and to hang up (H). ATDT !1234;H <Enter> Wait for an Answer (@) Some online services answer the phone and return a tape-recorded request for information before processing trans actions. In such instances, the @ command can be used in the Dial string to tell the modem to detect at least one ring, wait for five seconds of silence at the other end of the call, and then continue to execute the Dial string. To use the @ command, set the modem to X3 or X4. If the modem is set to X2 or lower, the modem returns an ERROR mes sage when encountering the @ character in a command string. In the next example, the modem is set to the X4 result code option and dials a banking service. Each occurrence of @ in the example indicates a five-second wait for silence, that is, for taped requests from the bank for a password (12345), an account number (6789) and a transaction code (2). The transaction code might indicate, for example, a request for an account balance. ATX4 DT5551234 @ 12345 @ 6789 @ 2 <Enter> If the necessary conditions do not occur_no rings, or no following five seconds of silence_the modem times out as it normally would (after 60 seconds). It then sends the message NO ANSWER to the screen and aborts the command. Reversing Originate/Answer Frequencies (R) This command allows calls to an originate-only modem. It reverses the modem's originate/answer frequencies, forcing the Sportster 14,400 to dial out at the answer frequency. The command follows the Dial command, before or after the phone number. AT D1234567R <Enter> AT DR1234567 <Enter> Dialing the Stored Number (DS) Chapter 5 includes instructions for storing a frequently-used telephone num ber in nonvolatile random access memory (NVRAM). To have the modem dial a stored number, use the DS command. ATDS <Enter> Redialing (A/) The most frequent reason for redialing is receipt of a busy signal. Use the A/ command, which does not take the AT prefix or a Carriage Return, to redial. A/ When the modem receives a command, it stores it in its command buffer until it receives the next AT command. Note that if you've sent the modem an additional command since the Dial command, A/ repeats that command instead of redialing. ESCAPE CODE OPERATIONS (+++) Once the modem is online to another system, the only command it recognizes is an escape code of three pluses, which forces the modem into online-command mode. Issue the command in the following sequence. ∙ Wait one second after sending the last item of data ∙ Type: +++ ∙ Wait one second before typing any data Do not type the AT prefix or a Carriage Return. The guard time of one second before and after the code prevents the modem from misinterpreting the presence of +++ in the transmitted data stream. If necessary, the character used in the escape code or the duration of the guard time can be changed by resetting Register S2 or S12. See the S-Register Summary in Appendix B. Modem Response to +++ When the modem receives +++, by default it enters online-command mode and returns the OK result code. It maintains the connection and is ready to act on commands. You may then choose one of the following options. ∙ Issue commands to the modem and then return it online. This operation is explained below under Returning Online. ∙ Hang up the modem, explained in the next section. Alternatively, if you want the modem automatically to hang up on receiving the +++ escape code, set S-Register S14 to 1 (ATS14=1). The modem disconnects and sends the NO CARRIER result code to the screen. Hanging Up (Hn) At its default setting, the escape code forces the modem into online-command mode but leaves the line open. To hang up the modem, issue the following command, with or without the zero, once the modem sends the OK result code. ATH <Enter> [or ATH0 <Enter>] H0 Hang up (go on hook). H1 Go off hook. If you want to issue commands to the modem and have it return online, use the next option. Returning Online (On) After forcing the modem into online- command mode with the escape code sequence, you can issue commands and then toggle the modem back online with the O command, as in the following example. AT Q1 O <Enter> [or AT Q1 O0 <Enter>] O0 Return online (normal). O1 Return online and retrain. If errors occur during a non-ARQ connection, try this option. The modem returns online and requests that both modems resynchronize. O2 Return online and shift rates. If errors occur during a non-ARQ, 2400- bps connection, and the remote modem also supports this O2 feature, use it to force the modem to shift down to 1200 bps for more reliable data transfer. As line improvements occur, the modems can be forced to shift up again to 2400 bps: send the +++ code and, after receiving the OK code, send ATO2. This feature is part of the CCITT V.22 bis recommendation, but is not commonly implemented. Make sure that the remote modem has the capability of shifting between 2400 and 1200 bps before using this option. AUTOMATIC ANSWERING The Sportster 14,400 is shipped with DIP switch 5 DOWN, Auto Answer suppressed. To set the modem to automatically answer incoming calls, do one of the following. 1.Before powering on the modem, set DIP switch 5 UP. When you turn the modem on, the modem answers incoming calls on the first ring. 2.When the modem is on, use software control. The following command instructs the modem to answer on the first ring. (You can substitute a higher value. See the S-Register Sum mary in Appendix B.) ATS0=1 <Enter> When the modem senses a call coming in, it sends the result code RING to your screen, goes off hook, and sends the remote modem a high-pitched answer tone. If there is no Carrier Detect within 60 seconds, the modem hangs up. If the connection is made, the modem returns a CONNECT result code. When the call is disconnected by you or the remote user, the modem hangs up and returns the NO CARRIER code. Suppressing Auto Answer To disable Auto Answer, reverse Steps 1 or 2 above: set DIP switch 5 DOWN before powering on the modem, or set the modem to answer on zero rings. ATS0=0 <Enter> Manual Answer If you've disabled Auto Answer but are expecting an incoming data call, use the Manual Answer command. Send the modem the following command after the RING result code appears on your screen. ATA <Enter> When the call is disconnected, the modem returns to its original state, Auto Answer disabled. Points to Remember 1.You can set the modem to receive calls when you're not at your computer or terminal. Load your communications software as you normally do, and set the modem to Auto Answer. Also set your soft ware's file-save function to save incoming messages and/or files. 2.If you've attached your phone so it can be used for conventional calls, disable Auto Answer when you are not expecting incoming data calls. Otherwise, your modem may answer the phone before you do, greeting a voice caller with a high-pitched, irritating answer tone. INTERNATIONAL CALLS The following commands apply to international calls. CCITT/Bell Answer Sequence (Bn) To answer international calls, use the default B0 setting. B0 This setting is required for V.32 bis modems to answer V.32 bis calls. It also selects the CCITT V.25 answer sequence, used outside of North America. The B0 setting does not affect the modem's ability to call or answer domestic modems. It takes slightly longer, however, to connect. B1 This setting selects the Bell 2225 Hz answer tone used in the U.S. and Canada, but will prevent your modem from answering domestic or international V.32 bis calls. Guard Tone (&Gn) British phone switching systems require answering modems to send an 1800 Hz guard tone after they send an answer tone. Some other European phone networks require a 550 Hz guard tone. Guard tones are not used in the United States or Canada. &G0No guard tone, U.S./Canada. Default. &G1550 Hz guard tone follows answer tone. Requires B0 setting. &G21800 Hz guard tone follows answer tone, United Kingdom and some Commonwealth countries. Requires B0 setting. Pulse Dial Make/Break Ratio (&Pn) This command sets the ratio of the off- hook/on-hook (make/ break) interval for pulse dialing. The default sets the modem for use in North America. The ratio must be changed if the modem is used to dial out in the United Kingdom and some Commonwealth countries. &P0Make/break ratio, U.S./Canada: 39%/61%. Default. &P1Make/break ratio, United Kingdom, some Commonwealth countries: 33%/67%. CCITT V.21_300 bps Select this option to call or answer overseas modems at 300 bps. In V.21 mode, the modem answers Bell 103/V.21 calls, but only originates V.21 calls. This option is enabled in Register S27 with the following command. ATS27=1 CCITT V.23_1200/75 bps Some United Kingdom applications require a 1200-bps speed with a 75-bps back channel. This option is enabled in Register S34 with the following command. ATS34=8