





                                                                COURIER HST


                                                                 APPENDIX E
                                         ADDITIONAL OPERATIONAL INFORMATION


          CONTENTS
          
          E-1  Using Both Voice and Data Communications

          E-2  High Speed/Low Speed Protocol

          E-3  Retrain Sequence

          E-4  PBX, Dedicated Line, and Leased Line Operations

          E-5  Hewlett Packard 300 Installations

          E-6  Analog Loopback and Other Testing



































                                                                        E-1










                                                                COURIER HST


          APPENDIX E-1
          USING BOTH VOICE AND DATA COMMUNICATIONS

          When you assemble the Courier, you have the option of plugging
          your phone into the second modular jack of the modem so it's
          available for voice calls.  You can also use the phone to
          synchronize communications with another user whose modem uses the
          AT command set, such as a USRobotics or USRobotics-compatible
          modem.

          PREPARATION

          First call the other user to establish the bit rate, parity, word
          length and number of Stop bits the other person's modem accepts.
          Then both of you can turn the call over to your modems.

          COMMANDS

          1.   Without hanging up the phone, have your modem go off hook in
               Originate Mode.  Type the following command:

                    ATD <Enter>

               NOTE:  Be sure the modem is not set to X2, X4, X6, or X7, or
               it will return the NO DIAL TONE result code and hang up.

          2.   The other party should then have the remote modem go off
               hook in Answer Mode.  The following command is used to do
               this:

                    ATA <Enter>

          3.   Now both of you can hang up your respective phones while the
               two modems establish the data link.  They will maintain the
               link until one of you gives your modem a command to
               disconnect.

          Either party's device can be the originate or answer modem:  it
          doesn't matter who made the phone call.  But one modem must first
          enter Originate Mode and the other then enter Answer Mode.  You
          and the other party, therefore, must agree on which command, ATD
          or ATA, you will each use.

          NOTE:  It may happen that spurious garbage characters will
          appear on the screen when you hang up the phone.  You can avoid
          these by hanging up the phone as soon as you hear the modem go
          off hook, during the one or two seconds it takes the two modems
          to establish the link.




                                                                        E-2










                                                                COURIER HST


          APPENDIX E-2
          HIGH SPEED/LOW SPEED PROTOCOL

          OVERVIEW

          This appendix is intended for those users who want to try
          programming their computers to switch bit rates to match the
          Courier HST's connection rate.  The material here applies only
          when the modem is set for variable rates at both the DTE
          (computer) and link interfaces, &B0 and &N0, respectively.

          In both Originate or Answer Modes, if the link rate is set to &N0
          the Courier HST negotiates with the remote modem to connect at
          the highest possible rate.  In addition, if the modem is set to
          the Extended or Advanced result codes (X1 or higher) it signals
          the DTE with one of the following result codes or, unless the
          call is at 300 bps, an /ARQ Mode equivalent:

               CONNECT        (300 bps)
               CONNECT 1200   (1200 bps)
               CONNECT 2400   (2400 bps)
               CONNECT 9600   (9600 bps)

          The modem sends the result code at its previous rate.  Then it
          switches to the new connection rate.

          If your computer doesn't switch rates and you want to program it
          to do so, use the example on the next page as a guide.  It
          demonstrates the occurrence of the CONNECT codes in the
          connection sequence, so that recognition of the codes can be used
          to switch the computer.  The example uses a sequence of incoming
          calls, but the codes apply to Originate Mode connections as well.

          The example assumes the following settings:

               Software: initially 9600 or 19.2k bps, allowing the full     
                         range of link rates:                               
                         9600/7200/4800/2400/1200/300 bps

                  Modem: X1 or higher (rate-specific CONNECT codes)
                         &B0 (variable DTE rate)
                         &N0 (variable link rate)










                                                                        E-3










                                                                COURIER HST


          Example

          -----------------------------------------------------------------
                                        Modem                  DTE/DCE
          Action                        Response                 Rate
          -----------------------------------------------------------------
          1.  Power on.                                          9600
          
          2.  300-bps call comes in.    RING                     9600
                                        CONNECT                  9600
          
          3.  Data link is established.                           300
              Data transfer takes place.
          
          4.  Data session is over.     NO CARRIER                300
              Call is ended; loss of
              carrier.
          
          5.  2400-bps call comes in.   RING                      300
                                        CONNECT 2400              300
          
          6.  Data link is established.                          2400
              Data transfer takes place.
          
          7.  Data session is over.     NO CARRIER               2400
              Call is ended; loss of
              carrier.
          
          8.  9600-bps call comes in.   RING                     2400
                                        CONNECT 9600             2400
          
          9.  Data link is established.                          9600
              Data transfer takes place.
          
          10. Data session is over.     NO CARRIER               9600
              Call is ended; loss of
              carrier.
          -----------------------------------------------------------------

          Explanation

          1.   The modem is powered on and is operating at 9600 bps.  If
               the software is then set to 19.2k bps and an AT command
               sent, the DTE/DCE rate would be 19.2k bps.

          2.   A 300-bps modem calls.  The Courier senses the incoming
               signal and sends the messages RING and CONNECT to the
               computer.  These messages are sent at 9600 (or 19.2k) bps,
               the current rate.



                                                                        E-4










                                                                COURIER HST


          3.   Since the Courier responds CONNECT, rather than CONNECT
               1200, 2400, or 9600, the computer switches to 300 bps.  The
               modem automatically shifts to 300 bps to accept the data
               from the incoming call.

          4.   The 300-bps data session is terminated; the modem sends the
               message NO CARRIER at 300 bps.

          5.   A 2400-bps call comes in.  The modem responds RING and
               CONNECT 2400.  These message are sent at the current bit
               rate of 300 bps.

          6.   The computer, receiving the CONNECT 2400 message, adjusts
               accordingly to the higher bit rate.  The modem also shifts
               to 2400 bps.

          7.   The 2400-bps data session is terminated; the modem sends the
               message NO CARRIER at 2400 bps.

          8.   A 9600-bps call comes in.  The modem responds RING and
               CONNECT 9600.  These message are sent at the current bit
               rate of 2400 bps.

          9.   The computer, receiving the CONNECT 9600 message, adjusts
               accordingly to the higher bit rate.  The modem also shifts
               to 9600 bps.

          10.  The 9600-bps data session is terminated; the modem sends the
               message NO CARRIER at 9600 bps.

          NOTE:  If online fallblack occurs during a 9600-bps call, the
          modem does not send CONNECT result codes for 7200- or 4800-bps
          link rates.

          Keep in mind that whether or not your computer adjusts to these
          rate changes, the Courier automatically shifts to the connection
          rate if it is set to &B0.















                                                                        E-5










                                                                COURIER HST


          APPENDIX E-3
          RETRAIN SEQUENCE

          DESCRIPTION

          The retrain sequence occurs at 2400 and 9600 bps.  It is a
          resynchronization sequence performed when one of the connected
          modems senses that problems on the line may affect data
          reliability.  The procedure is essentially transparent to users.

          The following is an example of retrain events:

          1.   The Courier HST's receiver, sensing a need to retrain,
               clamps RX to MARKs.

          2.   The remote modem, after receiving about 100 ms of analog
               signals (a pattern of ?~?~ is usually output), clamps RX
               data to MARKs.

          3.   After the training sequence, approximately one second, the
               Courier unclamps RX data and turns HS ON.

          4.   The remote modem reenters Data Mode.





























                                                                        E-6










                                                                COURIER HST


          APPENDIX E-4
          PBX, DEDICATED LINE, AND LEASED LINE OPERATIONS

          The following operations apply in installations where the modem
          is not directly connected to the public-access switched telephone
          network.

          PBX Installations

          It's possible to install the modem(s) on the customer side of an
          analog PBX.  When used with multiple telephones per line, DIP
          switch 7 can be set DOWN to short A/A1 when the modem is off
          hook.  This notifies other devices sharing the line that the line
          is busy.

          Calling an Outside Party

          To have the modem make an outside call, follow the auto-dial
          instructions in Chapter 6, but insert the sequence used to obtain
          an outside line, followed by a comma, before the phone number in
          the Dial command.

          The off-hook indicator on the PBX should show the extension as
          busy if DIP switch 7 is DOWN.

          Internal Calling

          To call another modem on the PBX system, use the Dial command
          described in Chapter 6 with the extension of the destination
          modem.  If set to Auto Answer, the called modem automatically
          answers on the incoming ring.

          The off-hook indicators on the PBX should show both extensions as
          busy if DIP switch 7 is DOWN on both modems.

          2-Wire Dedicated (Private) or Leased Line

          A 2-Wire dedicated (private) line is a customer-installed,
          twisted-pair line.  2-Wire leased lines are provided by the
          telephone company and may be designated as 2-Wire 3002 Analog
          Circuits.

          In both types of installation there is a continuous point-to-
          point connection between two modems.  For optimal operations, the
          physical length of the line should not exceed 5 miles.

          To establish the connection, follow these steps:

          1.   Decide which modem is to be the Originate modem and which
               the Answer modem.  The originate and answer frequencies must
               be defined for the modems to communicate.

                                                                        E-7










                                                                COURIER HST


          2.   First put the calling modem in Originate Mode with the
               manual Dial command:

                    ATD <Enter>

               NOTE:  Be sure the modem is not set to X2, X4, X6, or X7, or
               it will return the NO DIAL TONE result code and hang up.

          3.   Then put the answering modem in Answer Mode with the manual
               Answer command:

                    ATA <Enter>

          NOTE:  If there is an interruption in the communications link (a
          strike to the line due to weather or some other problem), repeat
          steps 2 and 3 to reestablish the link.




































                                                                        E-8










                                                                COURIER HST


          APPENDIX E-5
          HEWLETT PACKARD 3000 INSTALLATIONS

          The Courier HST recognizes the ASCII ENQ/ACK characters exchanged
          between the Hewlett Packard 3000 host computer and its terminals.
          The HP host sends the terminal an ENQ character at predefined
          intervals, and sends no more data until the terminal responds
          with an ACK character.

          Courier HST modems manage this ENQ/ACK protocol so that
          communication is speeded up, thereby enabling HP terminals to
          achieve high speeds on dial-up lines.  Special Received Data flow
          control settings (the &I command) are required for HP users.

          Follow these guidelines:

          1.   Use one of the &I settings given here for both Normal and
               error control (ARQ) sessions, i.e., for all &M settings.

          2.   Do not use a software setting for Transmit Data flow
               control.  Set the modem only to &H0 or &H1, according to the
               guidelines in Chapter 4.

          3.   Set the Courier HST to Host Mode if it is attached to the
               host computer, or to Terminal Mode if it is attached to a
               terminal:

               Host Mode      AT&I3 <Enter>  
               Terminal Mode  AT&I4 <Enter>























                                                                        E-9










                                                                COURIER HST


                                                               APPENDIX E-6
                                            ANALOG LOOPBACK AND OTHER TESTS


          ANALOG LOOPBACK SELF-TEST

          This test is a way to check that the modem's transmitter and
          receiver are working properly.  During Analog Loopback, data from
          the computer is sent in a loop through the transmitter (where it
          is modulated) and the receiver (where it is demodulated), and
          returned to the screen.  Due to asymmetrical modulation at 9600
          bps, the test must be performed at 2400 bps or below.

          You can use the modem's internal test pattern as data, or type
          your own at the keyboard.  Follow these procedures to test the
          modem by sending the test pattern:

          NOTE:  If the modem is set to X2, X4 X6, or X7 it will return the
          NO DIAL TONE result code and hang up.  Send the modem a different
          X setting.

          1.   Set your terminal or software to 2400 bps and send the modem
               the following command, which has the results listed below.

                    AT &M0 S16=5D <Enter>

               &M0     Sets the modem to Normal Mode.  If the modem is set
                       for error control (&M4 or &M5) you can't tell if
                       there is a problem because the modem checks for
                       errors and automatically retransmits any errored
                       data.
               S16=5   Sets S-Register 16 to Analog Loopback with test
                       pattern.  The modem sends, modulates and demodulates
                       its internal test pattern and returns that pattern
                       to your screen.
               D       The Dial command selects testing the Originate
                       (Dial) frequency.  The Answer command (A) tests the
                       Answer frequency.
               
               The modem enters Analog Loopback Mode, goes off hook, sends
               the message CONNECT 2400 to the screen, and then sends the
               test pattern.

          2.   When you're satisfied with the test, terminate the operation
               by pressing any character key on the keyboard.  The modem
               goes back on hook and responds with the message NO CARRIER.

          3.   Reset the error control default and reset S-Register 16 to
               zero, for data operations, by entering this command:

                    AT &M4 S16=0 <Enter>

                                                                        E-10










                                                                COURIER HST


          Normal/Test Frequencies

          In normal operations, communicating modems transmit at different
          frequencies within the communications channel, one low and the
          other high.  The calling modem is said to be in Originate Mode:
          it transmits at the low (Originate) frequency and receives at the
          high  frequency.  The answering modem, in Answer Mode, transmits
          at the high (Answer) frequency, and receives on the low
          frequency.

          During Analog Loopback testing, the modem transmits and receives
          on the same frequency, either Originate (low) or Answer (high).
          The Analog Loopback command in the previous section tests the
          Originate frequency.

          Testing the Answer Frequency

          To test the Answer frequency, substitute the Answer command, A,
          as follows:

                    AT &M0 S16=5A

          ADDITIONAL TESTS

          In all, S-register 16 has five settings, as follows.

               0    Data Mode (normal operations)
               1    Analog Loopback
               2    Dial Test
               4    Test Pattern
               5    Analog Loopback with Test Pattern

          NOTE:  After any testing, be sure to reset S-register 16 for Data
          Mode, with or without the default error control setting (&M4):

                    AT &M4 S16=0 <Enter>

          S16=1

          1.   Select this option to perform analog loopback testing by
               sending your own data instead of the test pattern.  Use
               either of the following commands after setting your terminal
               or software to 2400 bps.  If the modem is set for error
               control, insert &M0 before the S16 command.

                    ATS16=1D <Enter>
                    ATS16=1A <Enter>
                    
          2.   When the modem displays the message CONNECT 2400, type any
               message you wish at the keyboard.  It is looped through the
               modem and returned to the screen.

                                                                        E-11










                                                                COURIER HST


          3.   End the test by not typing anything for at least one second
               and then typing the escape code that brings the modem back
               to Command Mode.  (Do not type the AT prefix or press the
               Enter key.)

                    +++

          4.   The modem returns the OK message. Reset the error control
               default and reset S-Register 16 to zero, for data
               operations, by entering this command:

                    AT &M4 S16=0 <Enter>

          S16=2

          The Dial Test is used for factory testing the frequencies of
          Touch-Tone values.  When S-register 16 is set to 2 and a single
          Touch-Tone is dialed (e.g., ATD7), the modem continues to
          transmit that tone until another Carriage Return is entered.

          S16=4

          The Test Pattern alone is used for testing equipment and the
          phone line.  If S16 is set to 4 and a Dial command issued, the
          Courier transmits the test pattern upon connection to the remote
          system.  If set for Auto Answer the Courier transmits the test
          pattern when it answers a call.  Be sure to reset S16 to zero for
          normal calls.

          Testing at 1200 BPS

          To test the modem at 1200 bps, follow the previous instructions,
          but first set your software to 1200 bps.

          Testing at 300 BPS

          The Test Pattern is not available at 300 bps.  Analog Loopback
          testing is done at 300 bps by setting your software to 300 bps
          and setting S-16 only to 1D or 1A.

          NOTE:  It might happen that you have issued either S16=1 or 5 and
          the modem is in Analog Loopback Mode, but you haven't yet sent a
          Dial or Answer command to initiate testing.  If the modem is also
          set for Auto Answer and a call comes in, the Courier resets S16
          to zero and answers the call.







                                                                        E-12




