
        What a Modem Does
        -----------------

        The way calls were made with older telephone systems illustrates
        how modems make connections. By taking the receiver off the
        hook, then turning a crank, you got an operator to come on the
        line. You told the operator the number you wanted, and waited
        for the call to be placed for you. Until the person on the other
        end picked up the receiver, you stayed connected to the
        operator. The operator generally reported the progress of the
        call, then gave the line to you to wait for the person on the
        other end to answer. Your modem, like the operator, responds to
        your commands to dial a number or answer a call, then gives the
        line to your computer to begin data communications when the
        connection is made.

        Why You Need Communications Software
        ------------------------------------

        Like telephones that store the numbers you frequently dial,
        communications software automates your connections. This can
        range from saving numbers in a "telephone book" so you don't
        have to look them up and enter them each time handling the
        complete process from dialing through file transfer.

        You can use what is called "terminal emulation" software to
        issue modem commands that set up the modem and dial a number,
        but just as you make selections from within your word processor
        or spreadsheet software to use a printer, the easiest most
        effective way to use your modem is through communications
        software. Once you've made the connections to your computer and
        the telephone lines, you can almost forget the modem is there,
        and access its features through the software. In the same way
        you don't have to issue commands directly to the printer, you
        can simply reach for the printout, knowing that the software has
        taken care of everything. Your new modem will work with nearly
        any communications software designed for personal computers.
        Regardless of its level of sophistication, software is required
        to provide the link between your modem and the computer's
        keyboard.

        If your software has a problem communicating with the modem,
        you'll know when you start the program or when you run the
        software's installation procedure. A message like "modem not
        responding", means the software is not recognizing the modem. If
        you've made the port selection with the software and still can't
        make a connection, you'll need to use the software to manually
        change some of the settings that control how the modem operates.

        Most programs have an option for setting a modem
        "initialization" or "command" string to set the modem up to talk
        to the computer the way the software expects. The changes will
        probably involve the way the modem and the computer use the
        signals to talk to each other across the cable that connects
        them. Most programs that do not work with the modem's factory
        settings will operate properly if you change the way the modem
        uses the signal on the DCD and DTR line. For example, at the
        command line or window in which you adjust these settings,
        simply type AT&C1&D2, or add &D2&C1 to the string. If the string
        contains &K3, &F, or &W remove them. (These ampersand-letter-
        number combinations are modem AT commands.) The software will
        use the AT commands you put in this string each time it sets up
        the modem.

        For software that requires additional modem setup, refer to the
        software manual for specific descriptions of the settings that
        need changing. Two additional settings that 
        frequently need to be adjusted are result code display (messages
        the modem send in response to commands), and local character
        echo (the way your commands are displayed on the screen). These
        and other options are easily specified with an initialization
        string, or with the AT Command Set described in the following
        pages. If your software requires more settings to be changed,
        check your software's user's guide, then refer to the sections
        that follow for the particular command option. With the setup
        string in place, you will be able to use your software to place
        and answer calls to go on-line with another computer without
        issuing the commands to setup the modem each time you start the
        program.

        How to "Talk" to the Modem
        --------------------------

        If you find it necessary to communicate directly to the modem to
        set it up or to initiate calls, you are probably using terminal
        emulation software. This means that the only function the
        software provides is linking your keyboard input directly to the
        modem. This would be like connecting your printer directly to
        your keyboard; what you type would appear on the screen, and be
        sent out to the printer.

        Unless you have selected the option that some programs call
        "local mode" or "go local", communications software does not
        operate in this way. For certain uses, like determining whether
        there is a problem with your modem, the software, the line, or
        the other modem, this is a helpful way of talking to the modem.
        The next sections explain in detail how to setup your modem and
        initiate and answer calls using AT Commands once your software
        has linked your keyboard to the modem.

        Issuing AT Commands
        -------------------

        The Hayes Standard AT Command Set for intelligent modems is the
        language understood by modems used with most personal computers.
        AT commands can be used to set up the modem to suit the way your
        softawre and/or computer wants it to be configured. They can be
        used for dialing or answering. However AT coomands are not used
        to perform communications activities like sending a file. Once
        on-line, you'll be talking with another computer. The command to
        break the connection is probably the only instruction you would
        issue after going on-line.

        AT Command Format
        -----------------

        Modem commands begin with an AT prefix that gets the modem's
        attention (also tells the modem the speed and character format
        of the data coming from the computer). The AT prefix is followed
        by the command(s). The modem executes the command line when you
        press the key on your keyboard that you normally use to send
        commands. The command descriptions here show this key as <CR>,
        although it may be labeled on your keyboard as carriage return,
        Enter, or Return Key. For example, the command line ATV0<CR>
        gets the modem's attention and uses the V0 command option to
        tell the modem to display the responses to commands (result
        codes) as numbers rather than as words (the V1 option is the
        factory setting). The <CR> send the command to the modem.

        Many commands are used to select between two or more options.
        Numeric parameters indicate the form of the command you want to
        be in effect. If you issue a command without specifying a
        numeric parameter, the modem assumes the 0 command option. For
        example, Q0 tell the modem to respond to commands with result
        codes. Issuing Q1 tells the modem not to respond to result codes
        (some software programs call this "quiet mode").

        A command line can contain as many as 40 characters (the AT, 
        spaces, and the <CR> are not counted).  The command prefix can be 
        entered in either all upper case or all lower case letters, but 
        not in a combination (e.g., AT or at, but not At or aT).
        
        If you need to change something in the line before entering the 
        <CR>, use the backspace key.  To abort the command line, hold down
        the key your computer recognizes as the control key (ctrl) and 
        press "x."  The modem will return OK without executing the 
        command(s) on the line.  
        
        Moving Between Command and On-line States
        -----------------------------------------
        
        Before beginning communications or after "hanging up," the modem 
        is in command state, ready to accept configuration commands or to 
        go on-line when you instruct it to dial the number of a remote 
        modem.  You may also place the modem in command state from the 
        on-line state without breaking the connection. 
        
        Escape Sequence --  (+++)
        --------------------
        
        Not actually a command, the escape sequence tells the modem to 
        "escape" or leave the on-line state and enter the command state.  
        The sequence consists of a single character issued three times in 
        succession.  A one second "guard time" interval prevents the modem
        from mistaking a ramdom occurrence of of the same three characters
        as the escape sequence.  The character used in the sequence and 
        the duration of the guard time can be changed by writing values to
        the modem's S-Registers (special memory locations described later 
        in this guide).
        
        To issue the escape sequence simply hold down the shift key and 
        press the plus key three times (+++).  Be sure to pause at least a
        second before and after issuing the three characters.  If 
        operating properly, the modem will return the OK result code as an
        indication it is ready to accept commands.
        
        On-Line Command - O
        ------------------
        
        This command returns the modem from command state to on-line state
        when a connection has been "escaped" but not broken.  If you have 
        placed the modem in command state and are still connected to the 
        remote system, issue ATO<CR> to go back on-line.  What you type 
        will then be transmitted to the modem attached to computer on the 
        other end of the line.  If the connection is broken, to go on-line
        again you must instruct the modem to re-dial the telephone number.
        
        Getting On-Line
        ---------------
        
        In the same way voice telephone calls are made, one of the modems 
        must originate the call, and the other must be set up to answer 
        the incoming call.  Either modem may originate or answer the call.
         The following examples illustrate how to use the modem to place 
         and answer calls from your computer.
         
        Originating a Call
        ------------------
        
        To originate a call with another system, issue the D command to 
        "dial" the number.  This command instructs the modem to go off 
        hook, claim the telephone line, and originate a call.  When you 
        issue dialing commands to the modem, the data is communicated to 
        the modem, but does not pass across the telephone line.
        
        The following dial modifiers specify the number and method the 
        modem uses to dial.
        -----------------------------------------------------------------
        T    Specifies Tone method for subsequent dialing; follows the
             D command and precedes telephone number; can be issued as a
             command separate from dialing string.
        
        P    Specifies Pulse method for subsequent dialings; follows the D
             command and precedes telephone number; can be issued as a
             command separate from dialing string. (factory setting).
                
        ,    Pause 2 seconds before continuing to process the characters
             in the dialing string.
             
        ;    Return to command state after dialing and maintain 
             connection.  This modifier is useful in situations like 
             electronic banking where the modem needs to stay in 
             command state to receive other connection instructions.
             
        0-9  Numbers and characters for the modem to dial.
        *,#
        -----------------------------------------------------------------
        
        A typical dial command such as as ATD,T5552368<CR> gets the
        modem's attention (AT), instructs it to go off hook to originate a
        call (D), pause 2 seconds (,), and use the tone method (T) to dial
        the telephone number (5552368).  The <CR> sends the commands to 
        the modem.
        
        Answering a Call
        ----------------
        
        Incoming calls to your modem can be answered in either of two 
        ways.  You can issue a command to the modem when you hear the 
        telephone ring.  You can also set up the modem to answer 
        automatically when it detects a number of rings.
        
        Answering Manually - A
        ----------------------
        
        To manually answer a call from a remote system, issue the A 
        command.  ATA<CR> instructs the modem to go off hook, take control
        of the line, issue an answer tone, and connect with the incoming 
        call.  This command is used when the phone is ringing and you are 
        expecting a modem call (rather than a voice call).
        
        Answering Automatically - S0=n
        ------------------------------
        
        One of the modem's S-Registers provides the capability for 
        automatic answer.
        
        The S0=n command ("0" is the number of the register or memory 
        location; "n" is the number of rings to wait before answering) 
        lets you specify the numbers of rings.  Setting S0 to a number 
        other than its factory setting of 0 configures the modem for 
        auto-answer.  The modem will then operate the same way as a 
        telephone answering machine, picking up the phone after it detects
        the specified number of rings.
       
        For example, ATS0=3<CR> sets up the modem to go off hook and issue
        answer tone (no ATA<CR> is necessary) when the modem detects the 
        third ring.
        
        Communicating While On-Line
        ---------------------------
        
        When you are connected (on-line), data is passed across the line 
        between the two computers.  Either party can type information to 
        the other.  Characters received by the modem on the other end of 
        the connection will be displayed to the screen.  The user on the 
        other end can also type characters to your screen.  Sentences and 
        words will mix on the screen, however, if you both type at the 
        same time.
        
        If you cannot see what you are typing, you will need to change the
        local character echo setting (see Configuration Options later in 
        this guide).
        
        Terminating a Call
        ------------------
        
        Whenever you are ready to end communications, you must issue the 
        escape sequence (+++) to place the modem in the command state.  
        Then use the H command to hang up: ATH<CR>.  This command puts the
        modem on hook and releases control of the line, so it can be used 
        by a telephone.
        
        Unexpected interruptions to communicate occur with modem 
        connections just as with telephone calls.  Line noise, equipment 
        malfunction, and user error can all contribute to disruptions in 
        communication.  The modem indicates a loss of connection with the 
        NO CARRIER result code.  To re-establish the connection, simply 
        re-dial the number.
        
        To interrupt call placement during the handshaking process, you 
        can press any key before the two modems connect.
        
        Monitoring Operation and Call Progress
        --------------------------------------
        
        When you send a command or issue the escape sequence, the modem 
        responds with a "result code."  If it understands the 
        instructions, the modem will return the OK result code; if it does
        not understand, the modem will return the ERROR result code.  The 
        modem also provides call progress messages to let you know how 
        your connection attempt is going:
                                                                                        
        -------------------------------------------------------------------
        Result Code                     Explanation
        -------------------------------------------------------------------
        0  OK                           Command reconized and accepted.
        
        1  Connect                      Connection established at 0-300 if
                                        X1, X2, X3, or X4 is selected(no 
                                        speed indicated if X0 is 
                                        selected).
                                        
        2  Ring                         Incoming Call
        
        3  No Carrier                   Carrier signal lost or not 
                                        detected.
                                        
        4  Error                        Command not recognized; command
                                        line exceeds 40 characters or in
                                        sn improper format; modem checksum
                                        incorrect.
                                        
        5  Connect 1200                 Connection established at 1200bps
                                        if X1, X2, X3, or X4 is selected.
                                        
        6  No Dial Tone                 Dial tone not detected when 
                                        expected.
                                                                                
        7  Busy                         Number dialed is use.
        
        -------------------------------------------------------------------
        
        The X command allows you to set up the modem for a variety of call
        progress monitoring options and corresponding result codes.  
        Regardless of the option selected, the modem will report the OK, 
        Connect, Ring, No Carrier, and Error result codes.  Other call 
        progress monitoring feature combinations, like reporting 1200bps 
        connections, detection of busy signal, and no dial tone can be 
        selected with the various command oprions.
        
        -------------------------------------------------------------------
        Result Code...          X0      X1      X2      X3      X4
        -------------------------------------------------------------------
        
        OK                      Y       Y       Y       Y       Y
        CONNECT                 Y       Y       Y       Y       Y
        RING                    Y       Y       Y       Y       Y
        NO CARRIER              Y       Y       Y       Y       Y
        BUSY                                            Y       Y
        NO DIAL TONE                    Y                       Y
        ERROR                   Y       Y       Y       Y       Y
        CONNECT 1200                    Y       Y       Y       Y
        CONNECT 2400                    Y       Y       Y       Y
        
        -------------------------------------------------------------------
        
        If you want the modem to wait for a dial tone before dialing, you 
        should select either the X2 or X4 command options.  Either of 
        these configures the modem to wait until it detects a dial tone 
        before proceeding; if it does not, it returns the NO DIAL TONE 
        result code.  The same is true for configuring the modem's 
        response to a busy signal; if X1 or X4 is selected, the modem 
        recognizes a busy signal from the other end and returns the BUSY 
        result code.  The X4 option provides full call progress 
        monitoring.  However, X0 is the factory setting because many 
        software programs expect 1200bps modems to be configured initially
        with the basic call progress capabilities and corresponding result
        codes.
        
        Managing Modem Configuration
        ----------------------------
        
        When your modem is first installed and powered up, it is 
        configured with the settings selected at the factory.  The options
        specified for each command and the value is each of the modem's 
        S-Registers determine how the modem operates.  The modem's factory
        settings suit a wide range of user applications, while taking 
        advantage of the modem's full capabilities.
        
        Creating a Special Configuration
        --------------------------------
        
        If your software or the system with which you are attempting to 
        connect required that you set up the modem to operate other than 
        with factory settings for commands and S-Registers, you can create
        a special configuration, or profile, by issuing AT commands.  The 
        configuration you create will be used until you issue commands to 
        change the settings, or reset the modem (either with the Z command
        or by unplugging/replugging it).
        
        Resetting the Modem
        --------------------
        
        If the modem ever seems to be set in a way that makes it not 
        communicate as it should, or if you simply want to restore the 
        factory settings, you can reset it with the Z command.  ATZ<CR> 
        performs a "soft reset," replacing values currently in S-Registers
        and AT command options to factory settings.  The modem's factory 
        configuration is also recalled when the modem is unplugged and 
        plugged back in, or if power is lost to the wall plug.  If you are
        experiencing any difficulty with the modem, you may wish to issue 
        the Z command before unplugging the modem or issuing the test 
        commands.
        
        Adjusting Modem Speed
        ---------------------
        
        Modem speed is measured in bits per second(bps).  For example, if 
        Hayes Personal Modem 1200 is operating at its highest rate, data 
        will be transmitted at 1200bps.  This speed is not set by an AT 
        command; it is the speed at which the software sends the AT prefix
        (within the range supported by the modem) that determines the 
        speed at which the modem attempts to make the next connection.  
        Some programs offer an option for transmission sprrd, often called
        "baud rate," to specify the speed of the connection.  The software
        sends the AT prefix at the desired speed.
        
        In addition, the transmission rate of the connection will be 
        determined by the highest common speed supported by the two 
        connecting modems.  For example, if the modem at the other end is 
        capable of a maximum speed of 300bps, the connection and data 
        transmission will be at 300bps, even if your modem can communicate
        at 1200bps.
        
        Choosing a Communication Standard
        ---------------------------------

        Communication standards are protocols that determine how the 
        modems perform their connection handshake and the format and 
        speed used to transmit data.  For example, connections at 
        300bps use the domestic 103 standard; connections at 1200bps 
        use the domestic 212A standard; connections at 2400 bps use the
        international CCITT V.22bis standard. Because standards are 
        closely linked to speed, the modem selects the appropriate 
        standard as it adjusts to the speed.
        
        Testing the Modem
        -----------------
        In addition to the diagnostics the modem automatically performs 
        each time it is powered up, the I command can be used to gain 
        information about the modem.
        
        I0              Modem reports Hayes product code.
        I1              Modem calculates and reports ROM Checksum (3-digit
                        number).
                        
        The results of these tests are primarily used by Hayes Customer 
        Service and certain software programs to determine the 
        manufacturer/model of the modem you are using, and its feature 
        set.
        
        Refer to the descriptions in the Personal Modem 1200/2400
        Installation Guide for troubleshooting suggestions.  If you are
        able to issue commands to the modem and it returns an OK result
        code, the modem is probably operating correctly.  If the modem 
        does not seem to be responding, try resetting the modem (see 
        above).
        
        Setting Local Character Echo
        ----------------------------
        
        Your computer and software combination may require that you adjust
        the character echo feature of your modem to provide display of 
        characters as you type commands, or to prevent double characters. 
        Two options are available:
        
        E0              Modem does not return (echo) characters from the 
                        keyboards to the screen when in command state.
        E1              Modem returns (echoes) characters typed from the 
                        keyboard to the screen when in command state 
                        (factory setting).
                        
        This command is effective only if you are entering instructions 
        from a command line.  The settings for this command do not affect 
        the display of characters while you are on-line with another 
        system.  The software must provide on-line character echo, if 
        desired.
        
        Adjusting Result Code Display
        -----------------------------
        
        The two commands below configure the modem's use of result codes.
        
        Q0              Modem responds to commands with result codes 
                        (factory setting).
                        
        Q1              Modem does not respond to commands with result 
                        codes.
                        
        V0              Modem reports result codes as numbers.
        
        V1              Modem reports result codes as words (factory 
                        setting).                        

        Some software requires that result codes not be displayed, or that
        they be returned as numbers rather than as words.
        
        Configuring Modem Signals
        -------------------------
        
        Some computers or software expects  settings for signalling 
        between modems and between the modem and the computer to be 
        configured in ways other than that set at the factory.  Any 
        special modem-to-computer signalling requirements should be 
        described by your software's user's guide or your computer's 
        owner's manual.
        
        The C command controls the modem's response to an incoming carrier
        signal over the line from the remote modem.
        
        C0              Modem ignores an incoming carrier signal; the 
                        transmitter carrier is always off.
                        
        C1              Modem turns the transmit carrier signal on and off
                        to reflect the presence of and incoming carrier 
                        signal.  When the modem originates a call, answers
                        a call, or is connected to another system, the 
                        signal is on, and is off when the modem is not in 
                        one of these situations (factory setting).
                        
        The &C command determines the way the modem uses the carrier 
        signal when controlling the Data Carrier Detect (DCD) line (pin 2 
        on modem-to-computer cable).
        
        &C0             Modem presumes the presence of the carrier signal 
                        and maintains the DCD signal on at all times.
                        
        &C1             Modem turns the DCD signal on when it detects a 
                        carrier signal from the modem on the other end of 
                        the telephone line, and off when it does not 
                        (factory setting).
                        
        The &D command selects the modem's response to signal sent from 
        the computer on the Data Terminal Ready(DTR) signal (pin 1 on the 
        modem-to-computer cable).
        
        &D0             Modem presumes presence of DTR signal and ignores
                        the actual status of the signal (factory setting).
                        
        &D1             Modem monitors DTR signal.  When communications 
                        software is used to cause an on-to-off transition 
                        of DTR signal, the modem enters command state and 
                        ignores AT commands.  When the software causes an 
                        off-to-on transition of DTR, the modem will again 
                        respond to AT commands and can be returned to the 
                        on-line state (if the connection has not been 
                        broken) with the AT0<CR>.
                        
        &D2             Modem monitors DTR signal.  When communications 
                        software is used to cause an on-to-off transition 
                        of DTR, the modem will again respond to AT 
                        commands.
                        
        Writing to the Modem's S-Registers
        ----------------------------------
        
        S-Registers provide special access to setting that determine modem
        operation.  The factory-set values stored in these registers are 
        recalled and used to control the modem each time it is powered up 
        or reset.
        
        Aside from using S0 to store the number of rings for automatic 
        answer (described earlier), you will have little need to change an
        S-Register value.  However, if your use of the modem requires that
        one or more of these be changed, you can do so by using the Sr 
        command:
        
        Sr?             Modem reads and responds with the value of 
                        register "r" (r=number of register; "?" requests 
                        the value).
                        
        Sr=n            Modem sets the value of register "r" to "n" 
                        (n=value within the range of the register).
                        
        Writing to the modem's S-Registers is not recommended unless your 
        use of the modem requires that one or more of these settings be 
        changed.
        
        For your refrence, the modem's S-Registers, their function, ranges
        in units, and factory settings are provided in the chart below.
        
        -------------------------------------------------------------------
     S-Register       Number &          Units     Range        Factory                                    
                      Function                                 Setting
        -------------------------------------------------------------------
        S0      Ring to answer on       Rings      0-255         0
        S1      Rings received          Rings      0-255         0
        S2      Escape sequence         ASCII      0-127        43  
                character
        S3      Carriage return         ASCII      0-127        13
                character
        S4      Linefeed character      ASCII      0-127        10
        S5      Backspace character     ASCII     fixed at       8
        S6      Wait time for dial     seconds    fixed at       4 
                tone                        
        S7      Wait time for carrier  seconds    fixed at      45
        S8      Duration of comma      seconds    fixed at       2
        S9      Carrier detect         1/10 sec     1-255        6
                response time        
        S10     Delay between loss     1/10 sec     1-255        7     
                of carrier signal
                and modem hang up                       
        S11     Duration of DTMF        msec      fixed at      95             
                tones for dialing
        S12     Escape sequence        1/50 sec    20-255       50                       
                guard time
        S25     Delay between loss     10 mec       1-255        5
                of DTR signal and
                modem hangup        
        S30     Delay time from no      10 sec      0-255       60
                modem activity until
                auto hangup        
        -------------------------------------------------------------------
        
        Cable Connections
        -----------------
        
        The table below describes the pin number on the modem's cable, the
        direction the signal pass, and the name of the signal used by the 
        modem.
        
        -------------------------------------------------------------------
        Pin     Direction                       Signal
        -------------------------------------------------------------------
        1       From Computer                   DTR - data terminal ready
        2       To computer                     DCD - data carrier detect
        3       From computer                   TxD - transmit data
        4       Not applicable                  ground - signal ground
        5       To computer                     RxD - receive data
        6       To computer                     DSR/CTS - data set ready/        
                                                          clear to send
        7       To computer                     RI - ring indicator
        8       Not applicable                  ground - signal ground
        -------------------------------------------------------------------
        The housing of the connector provides a shield that reduces noise 
        and interference.
        
        The actual pin number on which a signal is carried will vary 
        depending on the adapter used.
        

        The table below cross-refrences the pin numbers used for signals 
        on the 8-pin DIN with those for the adapters provided with your 
        modem.
        
        -------------------------------------------------------------------
        Signal            DIN-8           DB-9            DB-25
        -------------------------------------------------------------------
        
        DTR                 1               4              20                                                                         
        DCD                 2               1               8
        TxD                 3               3               2
        ground              4               5               7
        RxD                 5               2               3
        DSR/CTS             6               8               5
        RI                  7               9              22
        signal ground       8               5               7
        shield           shield          shield             1

        NOTE:  If you construct an adapter for use with the modem, consult
        your computer's owner's manual for the signals supported and the 
        appropriate pin numbering.
        
