One Technology Way P.O. Box 9106 Norwood, MA , U.S.A. Tel: Fax: Using TSM-100AL on Leased Lines

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1 AN8 APPLICATION NOTE One Technology Way P.O. Box 90 Norwood, MA 0090, U.S.A. Tel: Fax: Using TSM00AL on Leased Lines by Ajai Gambhir and Erik Hulsmans INTRODUCTION This application note discusses the leased line operation of the TSM00AL. This application note briefly describes the most commonly used method for operating the ADSST leased line modem and the reference design used. The ADSSTTSM00 AL reference design data access array (DAA) can be used on powered and unpowered (galvanic) leased lines. LEASED LINES DEFINED A permanent telephone connection between two points set up by a telecommunications common carrier is known as a leased line. Unlike normal dialup connections, a leased line is always active. The end points of the line are under the control of the user who can connect a modem at each end of the line. Because the connection does not carry any other communications, the carrier can guarantee a given level of quality. The leased line involves cables, such as twisted pair, coaxial, or fiber optic. This application note details how to configure the ADSSTTSM00AL modems to use a wire and wire twisted pair leased line. Leased lines are increasingly being used by companies and individuals in applications where a permanent or semipermanent connection is desired between two modems. In addition, leased lines are popular for data transfer or Internet access because they afford faster data transfer rates and are cost effective if the Internet is used heavily. Ordinary dialup modems for a telephone line do not normally work on such a leased line. A typical telephone line has about 0 V to 0 V of energy (the battery) when not in use, and a conventional modem uses this voltage for transmission. Furthermore, telephone companies have special signals indicating, for example, a ring or a busy line. Conventional modems expect and respond to these signals. Connecting two such modems by a long extended telephone wire does not provide the telephone signals on the cable and thus the modems do not work. The ADSSTTSM00 modems are designed to work on these lines. Leased line modems feature a dumb mode that ignore AT commands and disable result reporting. AT indicates attention and is a prefix for modem commands. One type of leased line uses two pairs of wires (one for each direction) using V.9 modulation at a 900 baud rate. Leased lines may or may not be equipped with a voltage supply. Powered Leased Lines A leased line with a source of voltage from a telecommunications company exchange is referred to as a powered leased line. Unpowered (Galvanic) Leased Lines A leased line without a source of voltage is called an unpowered leased line or a dry line. ADSSTTSM00 series modems can also work on these lines. For typical applications, both the originating and answering leased line TSM00 modems are positioned in the offhook state through commands issued from the respective controllers. Once a connection is established between originating and answering modems, the connection is usually left intact indefinitely. This means that even during periods of inactivity, such as when there is no data transfer between modems, a carrier tone remains present on the leased line. In the event that a power failure or if some other event occurs to terminate the connection, the leased line modem defaults to the onhook condition. Each controller must then reissue the commands to place the respective modems in the offhook state. It is also possible to instruct the modem to automatically reconnect at powerup. This setting must be stored in nonvolatile memory. The schematic in Figure shows the public switch telephone network (PSTN) DAA of the TSM00. The DAA can be used on powered and unpowered (galvanic) leased lines. Rev. 0 Page of 8

2 AN8 TABLE OF CONTENTS Introduction... Leased Lines Defined... Powered Leased Lines... Unpowered (Galvanic) Leased Lines... AT Commands and AT Registers... Register %S7: Leased Line Mode... Bits [B:B0]: Operation Mode Selection... Bits [B7:B]: DAA Selection... Register %S8: Calling Tone Mode... Application Note Bit B: Calling Tone Detection Enable... Bit B: Calling Tone Synchronization Enable... Bit B: Calling Tone FaxData Automode... ATA... ATD... Register S7... Register S... AT Command Example... Alternative Schematic... Bit B0: Calling Tone Generation Disable... Rev. 0 Page of 8

3 Application Note AN V CLK_OUT G[] DGND G[] DVDD G[7] XTALO AVDD 0 DSPCLK XTALI TX 9 BITCLK BIT_CLK AGND 8 SDATAIN SDATA_IN 7 SDATAOUT SDATA_OUT FILT ACSYNC 0 SYNC RX CODECRESET /RESET G[]/MIC AOUT G[]/MOU T G[0] G[]/MOU T G[] V L NOTE BLMAJ0SND G R9 0K R0 0K DIGITAL GND ANALOG GND R 0K C8 R 00nF 0K TXA VA R 0K R C 0K 00nF NOTE : Stuff Capacitors only when necessary for EMC compliance. NOTE : Stuff BLM if necessary for EMC, otherwise 0 E resistor. NOTE : Place analog ground plane under these components. NOTE : Safety barrier : isolation minimal.mm. G TXA RXA VA V VA C 00nF C0 NOTE C uf/v C9 R0 C 7nF R8 0 R7 70 D R K V SAFETY BARRIER NOTE R9 K R R 7 7 C nf 0V G C nf 0V L BLMAJ0SN A L BLMAJ0SND B NOTE V BZX8V C0 00nF U AD80 C nf C7 R 0K C8 00nF L BLMAJ0SND D BZX8V D U Y0SB BZX8V UB R AD809AR R 0K UA AD809AR R7 R8 0K C 00nF D Q BC8B 7 8 BZX8 C uf C7 C uf R9 R 0 R K9 T 7889R Q BCPTT C 0uF/V R8 M C 7nF R7 0 U Y0SB RV KUSN D SZB0 Figure. DAA Schematic for the TSM00 Rev. 0 Page of 8

4 AN8 AT COMMANDS AND AT REGISTERS REGISTER %S7: LEASED LINE MODE In leased line mode, Register %S7 controls the leased line options. Because %S7 is an offline register, it can only be written to in an offline state, that is, when the modem is on the dial page. Writing to this register brings the modem to PSTN or to one of the leased line modes. As part of the command line, the strap value can be stored in Flash memory. The strap reloads into the active profile at powerup, and thus the modem functions in the selected mode (LL or PSTN) after powerup. In addition, the register is used to control the DAA hardware. Some of the DAA hardware settings require specific hardware. Bits[B:B0]: Operation Mode Selection After writing to Register %S7, use AT&W commands to update the stored profile. After powerup, the stored profile loads. If Bit of Register %S7 is set, the modem attempts to connect automatically to the remote modem. Automatic connect mode with endless looping (S = 0) can be terminated by a DTR drop during training phase. Note that the in connect ATH or DTR drop can be used. Table. Operation Mode Selection Command Description PSTN The modem uses PSTN training. Leased Line (LL) Automatic Connect at PowerUp Application Note The modem uses leased line training. Use ATD to start the calling mode training and ATA to start the answer mode training. The modem automatically goes offhook and starts training after powerup, unless DTR is low. Bit B determines whether call or answer mode is used: 0 for answer mode (ATA) and for call mode (ATD). Note that no number is dialed in call mode because the functionality is intended for leased line connections. Bits[B7:B]: DAA Selection For the regular PSTN modem, only the PSTN and LL W (hook closed) options are available. The options LL W DAA and LL W DAA options are available only with special LL modem hardware. Table. DAA Selection Command Description PSTN DAA PSTN DAA is selected. LL DAAWIRE The leased line wire DAA is selected. LL DAAWIRE The leased line wire DAA is selected. Table. Description of Bits[B7:B0] for Register %S7 B7 B B B B B B B0 Comments x x x x x x x 0 PSTN training (default) x x x x x x x Leased line training x x x x x x 0 x No automatic connect at powerup x x x x x x x Automatic connect at powerup (leased line operation) x x x x 0 x x x Automatic connect in answer mode x x x x x x x Automatic connect in call mode x x x 0 x x x x PSTN DAA (default) x x x x x x x Leased line DAA x x 0 x x x x x Leased line wire DAA x x x x x x x Leased line wire DAA Rev. 0 Page of 8

5 Application Note REGISTER %S8: CALLING TONE MODE Register %S8 controls the calling tone operation. Bit B0: Calling Tone Generation Disable Setting Bit B0 = disables sending calling tones. The effect of this bit can be reversed using a modifier in the dial string. Bit B: Calling Tone Detection Enable Setting Bit B = enables the calling tone detector during and after the dial process. A message indicating fax or data is sent to the DTE, depending on the frequency of the incoming calling tone (00 Hz for fax, 00 Hz for data). The message is sent at the end of each calling tone burst. This feature only works after the ATA command, so the user has to disable the automatic answering feature by sending ATS0 = 0 to the modem first. When the word fax appears, the user can enter ATFCLASS =. The training begins by sending another ATA command to the modem. AN8 Bit B: Calling Tone Synchronization Enable Setting Bit B = enables the calling tone synchronization during the dial process and subsequent modem training. The answering modem waits until a sequence of three calling tone bursts is received before transmitting the 00 Hz answering tone. Calling tone synchronization can be used in leased line operation to synchronize the training. This feature only works after an ATA command, so if PSTN is used, the user first has to send ATS0 = 0 to disable automatic answering. Bit B: Calling Tone Fax Data Automode Note that the Bit B feature is currently not supported. Setting Bit B = enables automode between the fax and the data based on the calling tone frequency (00 Hz for fax and 00 Hz for data). Table. Description of Bits [B7:B0] for Register %S8 B7 B B B B B B B0 Comments x x x x x x x 0 Calling tone generation enabled (default) x x x x x x x Calling tone generation disabled x x x x x x 0 x Calling tone detection disabled (default) x x x x x x x Calling tone detection enabled x x x x x 0 x x Calling all tone synchronization disabled (default) x x x x x x x Calling tone synchronization enabled x x x x 0 x x x Calling tone fax DATA automode disabled (default) x x x x x x x Calling tone fax DATA automode enabled Rev. 0 Page of 8

6 AN8 ATA ATA starts the modem training in answering mode. ATA is an offline command. ATA skips the dialing procedure and launches the modem in answer training. ATD ATD starts the modem training in calling mode. ATD is an offline command. ATD skips the dialing procedure and launches the modem in calling training. REGISTER S7 Register S7 sets the maximum amount of time to wait for the carrier after dialing. This register gives the answer tone and silence timeout during dialing before hanging up. The unit is in seconds where the maximum is with a default of 7. In leased line mode, this register is used as a synchronization timeout (answer tone calling tone synchronization) between the calling and the answering modem. If the timeout expires, the modem restarts its training until the number of synchronization attempts is reached. REGISTER S Register S determines the number of synchronization attempts. In leased line mode, Register S defines the number of synchronization attempts before going idle. An endless loop is indicated when the number of synchronization attempts is equal to 0. AT COMMAND EXAMPLE The leased line settings can be controlled with Register %S8, Register %S7, Register S7, and Register S. Use following AT commands: AT%S8 = %S7 = 9&W0&Y0 ATD Set Register %S8 = Calling tone generation enabled, B0 = 0 Calling tone detection enabled, B = Calling tone synchronization enabled, B = Set Register %s7 = 7 Application Note Leased line training Bit B0 = Automatic connect at powerup, Bit B = Automatic connect in calling mode, Bit B = Hook relay closed Bits[B7:B] = Timeout is controlled with Register S7. This register is used for answer tone timeout in the calling modem and for calling tone timeout on the answering modem. If the timeout is expired, the modem restarts its training in any of the leased line modes until the number of synchronization attempts is reached. The number of synchronization attempts is controlled using Register S. The register defines the number of synchronization attempts before going idle. If the number of synchronization attempts is equal to 0, an endless loop is indicated. ALTERNATIVE SCHEMATIC An alternative leased line schematic (see Figure ) uses a PSTN DAA, a wire LL DAA, and a wire LL DAA. The transformer section of the LL interface is not shown. Rev. 0 Page of 8

7 Application Note AN8 V C 00nF U7 AD80 DIGITAL GND ANALOG GND C nf NOTE C7 R 00nF 0K TXA UB R 8 LMV9MT C uf VAC R7 0K UA WRX 0 VA R 0K R 0K C R 00nF 0K NOTE : Stuff Capacitors only when necessary for EMC compliance. NOTE : Stuff BLM if necessary for EMC, otherwise 0 E resisto r. NOTE : Place analog ground plane under these components. NOTE : Safety barrier : isolation minimal.mm. NOTE : HYBRID COMPONENT VALUES SHOWN FOR ETAL P0. RXA TXA FILT RXA FL0 VAC FL VAC V U VCC NC7SB7 VAC C7 uf T ETAL P0 or MIDCOM7889R MAKE DOUBLE FOOTPRINT LL_T VAC C 00nF LL_T C0 WRX GN D WRX R7 R TRANSFO C9 0n R0 R 7E C9 7nF/0V R 7E R K R9 K R 0 C uf/0v Q V 80pF SAFETY RV P00SB BC8B L BLMAJ0SND C0 80pF SAFETY R R K R K R K L BLMAJ0SND 7 S A A B C 00n F UC LMV9MT L BLMAJ0SND D 8 9 BZX8V D BZX8V R9 0K C8 00nF U VCC NC7SB7 B GND B0 B B0 Q BC8B D BZX8 S A R8 DSPCLK BITCLK SDATAIN SDATAOUT ACSYNC CODECRESET AOUT R9 R0 K K CLK_OUT G[] DGND G[] DVDD G[7] XTALO AVDD 0 XTALI TX 9 BIT_CLK AGND 8 SDATA_IN 7 SDATA_OUT FILT 0 SYNC RX /RESET G[]/MIC G[]/MOU T G[0] G[]/MOU T G[] R 0K C n R0 K R 0K C7 uf C9 uf C 7nF/0V R K PC8X P R C 8 R K UD LMV9MT C8 uf C0 C 80p C 7uF/V Q BCP C u/v R 0 D SZB0 U LMV9MT Figure. Alternative Leased Line Schematic Rev. 0 Page 7 of 8

8 AN8 Application Note NOTES 008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. AN0007/08(0) Rev. 0 Page 8 of 8