COURIER HST CHAPTER 6 DIALING AND ANSWERING BASIC REQUIREMENTS To successfully establish a communications link, the called or calling modem must be compatible with the following standards at the specified rates. Bits per Second Standard 9600 USR-HST or compatible 2400 CCITT V.22bis 1200 Bell 212A 300 Bell 103 To successfully exchange data, both modems must use the same 10- bit data format. The formats allowed are as follows: Start Data Stop Bits Bits Parity Bits 1 7 Even, Odd, 1 Mark, Space 1 7 None, Even, Odd, 2 Mark, Space 1 8 None 1,2 Transmission Rate In general, you should know the transmission rate of the other modem before calling. However, if the link rate is set to the default, &N0, and the remote modem is operating at a lower rate, the Courier falls back to the rate of the remote modem. This applies to both Originate and Answer Modes. See the discussion under Data Rate Commands, in Chapter 4. Error Control Always set the Courier HST for error control, &M4 (the default) or &M5, for 9600 bps connections. It's a good idea to find out if the remote modem is MNP- compatible at 2400/1200 bps. Some public network services, for example, are not. If the Courier HST is set to &M4 and dials a modem that isn't under error control, it operates in Normal Mode (no error control). However, if the remote modem doesn't support the MNP protocol at 2400 or 1200 bps, the MNP link-request signals may be misinterpreted and block a successful connection. 6-1 COURIER HST If you know the remote modem doesn't support MNP, we recommend setting the Courier HST to &M0 before dialing. Automatic Retrain An HST or V.22bis modem sends a retrain signal if it senses that a problem in the phone line connection may be causing data unreliability. The modems stop the transfer of data for about a second while they resynchronize, and then resume Data Mode operation. Retraining only occurs during 9600 and 2400 bps communications. For a description of the signaling sequence, see Appendix E-3. PLACING CALLS The commands discussed in this section are used in the following operations: Dialing D (0-9 # * , ; ! P T W @ R), DSn Redialing A/, A>, > Canceling dialing Dial (D) When the Dial command is issued the modem goes off hook -- the equivalent of your picking up the 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 command string may include up to 40 characters, plus the AT prefix and Carriage Return/Enter key. The modem doesn't count spaces. It counts punctuation characters such as parentheses and hyphens, but ignores them. The following command instructs the modem to stop the display of commands (E0, turn off the local echo), to dial (D) using Touch- Tone dialing (T), and to turn off the speaker (M0). The spaces shown are ignored by the modem and are only included here for readability. AT E0 DT 1234567 M0 Dialing Type (P, T) If set to X0 or X1, the modem defaults to pulse (rotary) dialing. To have the modem use tone dialing, use the T command, which also allows you to use the asterisk (*) and pound sign (#). The 6-2 COURIER HST command may be included in the Dial string, as in the above example, or issued separately: ATT The following command resets the modem to pulse dialing: ATP You can switch from one dial type to another within a dialing sequence. For example, you might have a phone line that only accepts pulse dialing (slower than Touch-Tone dialing) but subscribe to a long-distance service that accepts tone dialing, such as MCI. You can switch to tone dialing once you've hooked into the long-distance service. In the following example, a switch is made to tone dialing before entering a service account number and the long-distance destination. (The commas are discussed shortly.) ATDP 9,,7654321,,T 55555,,1 312 1234567 NOTE: The modem remains set for Touch-Tone dialing until it is reset or the ATP (pulse) command is reissued. Adaptive Dialing (X2-X7) When any of the X2 through X7 options is in effect and you don't issue a dialing type in the Dial string, the Courier uses tone dialing, which is faster than the default pulse type. However, if the phone company central office doesn't have Touch-Tone detection equipment, the modem can not "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,,T 55555,,1 312 1234567 The first four-second pause is to access an outside line after dialing 9, the second to make sure the remote computer 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. NOTE: A slash (/) can be used in any command string to have the modem pause for only 125 milliseconds. Some users find the 6-3 COURIER HST shorter delay of a series of slashes, rather than the 2-second comma pause, useful for certain applications. 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 Courier 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, issue the Dial command with a semicolon: ATDT5551234; When the modem returns the OK result, pick up your phone receiver so you can talk to the other party and tell the modem to hang up: ATH 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're finished, tell the modem to hang up. Dialing Letters (") Quotation marks are used to have 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: ATDT"BBS-NEWS If you're 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, i.e., 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 Command Mode (;) and to hang up (H). ATDT !1234;H 6-4 COURIER HST Wait for a Second Dial Tone (W) This command is useful in situations where you must wait for a second dial tone before entering a password, for example, when using MCI, Sprint, or other long-distance service. The following command tells the modem to dial the service number, wait for the second dial tone, dial the ID, pause two seconds, then place the long-distance call. ATDT 5551234 W 12345, 3121234567 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). Wait for an Answer (@) Some online services answer the phone and return a tape-recorded request for information before processing transactions. 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, X4 or X7. If the modem is set to X2 or lower, the modem returns an ERROR message when encountering the @ character in a command string. If set to X5 or X6, the modem hangs up when it detects a voice answer and sends the VOICE result code. 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 after taped 6-5 COURIER HST requests from the bank for the labeled items. The transaction code might be used, for example, to request an account balance. Password | ATX4 DT1234567 @ 12345 @ 6789 @ 2; | | Account # Transaction Code If the necessary conditions don't occur -- no rings, or no following five seconds of silence -- the modem times out as it normally would (after 30 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 Courier to dial out at the answer frequency. The command follows the Dial command, before or after the phone number: AT D1234567R AT DR1234567 CANCELING DIALING To cancel dial-command execution, press . 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 in the next section. REDIALING The most frequent reason for redialing is receipt of a busy signal. The Courier HST provides three ways to redial, as follows. Re-execute the Last Command (A/) The A/ command, which doesn't take the AT prefix or a Carriage Return, redials one time: A/ When the modem receives a command, it stores the instruction in its command buffer until the next AT command is received. Note that if you've sent the modem an additional command since the Dial command, A/ re-executes that command instead of redialing. 6-6 COURIER HST Automated Redialing (>, A>) These two commands, while they can be used to continuously repeat any command, are designed for automated redialing. The first (>) is included in the Dial command. The second (A>) is used alone to redial the command string in the buffer. Continuous Repeat (>) If you know the modem you're calling is frequently busy, include the Repeat command in the Dial string, as follows: AT > DT 1234567 AT DT 1234567 > The modem enters Repeat Mode, dials the number, waits the default 30 seconds for a carrier, and hangs up. Then, after a two-second pause, it redials. The cycle continues until the modems connect or the modem reaches a maximum of 10 attempts. The 10-try limit is mandated by the Canadian Department of Communications (DOC) to prevent tying up local telephone company exchanges with unconnected calls. Continuous Re-execute (A>) This command combines the features of both the A/ and > commands. The modem enters Repeat Mode as described above, and redials the Dial string in the command buffer. Like the A/ command, A> doesn't take the AT prefix or a Carriage Return: A> Exiting Repeat Mode Should you use > or A> with a command other than a Dial string, abort the cycle by pressing . To abort automated redialing, be sure to press when the result code appears, during the pause before the modem begins dialing again. If you press while the modem is dialing, that dial attempt is canceled but the cycle continues. DIALING A STORED NUMBER (DSn) Chapter 5 includes instructions for storing up to four telephone numbers in nonvolatile random access memeory (NRAM). To have the modem dial a stored number use the DSn command, where n is the number's position, 0-3, in NRAM. In the first of the next two 6-7 COURIER HST examples, the phone number is stored at position 0, assumed by the modem if there is no numeric parameter: ATDS ATDS3 If you've stored a long distance service number/access code, for example at position 1, use the DSn command to dial the number and code, and follow that with a Dial command to dial the call's destination. (The spaces are included for readability.) AT DS1 D 312 5556789 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 back to Command Mode: -- Wait one second after entering 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 occurrence 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 S-register 2 or 12. See Appendix B-5. Modem Response to +++ The modem returns to Command Mode when it detects the escape code. However, it keeps the line open or hangs up, depending on the setting of DIP switch 9: DIP Switch 9 Response to +++ UP Modem goes on hook (hangs up), sends NO CARRIER result code DOWN Modem maintains connection, sends OK result code (Factory Setting) Retain the factory-set position (DIP switch 9 DOWN) if you want the modem to execute commands and return online. (See the O command, below.) 6-8 COURIER HST If you want an automatic disconnect when you issue +++, set switch 9 UP. (If the modem is on, also issue the ATZ command.) An advantage of this is that you're not likely to inadvertently run up an all-night phone bill. WARNING For unattended modem operations: in rare instances, the modem may fail to recognize the +++ escape code sequence. If you are running the modem under software control for unattended operations, we suggest you use the surefire method of dropping the RS-232C DTR signal for at least 50 milliseconds, to ensure against costly phone charges. Methods of turning the DTR signal off, e.g., closing the communications port, differ from one computer to another. RETURNING ONLINE (O) If DIP switch 9 is DOWN (on detection of the escape code the modem maintains the connection), you can issue commands and then toggle the modem back online with the O command, as in this example: AT Q1 O HANGING UP (Hn) If DIP switch 9 is DOWN (factory setting), the escape code forces the modem back to Command Mode but leaves the line open. To instruct the modem to hang up, issue the following command once the modem sends the OK result code: ATH If DIP switch 9 is UP, the modem automatically hangs up on receipt of the escape code. AUTOMATIC ANSWERING The Courier HST 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, it answers incoming calls on the first ring. 2. If 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 summary in Appendix B-5.) 6-9 COURIER HST ATS0=1 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 30 seconds, the modem hangs up. If the connection is made, the modem sends 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, if it is powered on, use the command to set the modem to answer on zero rings: ATS0=0 Points to Remember 1. If the modem is attached to a computer, you can set the modem to receive calls when you're not there. Put the modem in Terminal Mode and set it for Auto Answer. Also set your software'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're 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 Courier HST has three settings which enable international calls. These settings do not apply to calls originating in the U.S. or Canada. U.S./CCITT Answer Tone (Bn) In the United States and Canada, modems use a 2225 Hz answer tone. Outside North America, most modems adhere to the CCITT V.25 standard and send out a 2100 Hz tone followed by a 2250 Hz tone. If you're expecting an overseas call, set the Courier to use the CCITT answer tone. The setting won't affect the modem's ability to connect with a domestic modem, although it will take slightly longer to connect with a calling modem. B0 CCITT answer sequence, used to answer calls calls originating outside North America. Required with &G2 setting. 6-10 COURIER HST B1 U.S. answer tone. Default. Guard Tone (&Gn) British phone switching systems require the modem to send an 1800 Hz guard tone after it sends an answer tone. The guard tone is not used in the United States or Canada. &G0 No guard tone, U.S./Canada. Default. &G1 Reserved. &G2 1800 Hz guard tone follows answer tone, United Kingdom and some Commonwealth countries. Requires B0 setting as well. 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 in the United Kingdom and some Commonwealth countries. &P0 Make/break ratio, U.S./Canada: 39%/61%. Default. &P1 Make/break ratio, United Kingdom, some Commonwealth countries: 33%/67%. 6-11