                    APPENDIX F.  MODEM TESTING

      

      Testing is available with the &T command
      or Register S16.  All loopback testing
      conforms to CCITT Recommendation V.54.
      Earlier USRobotics high speed modems,
      however, did not perform the &T test
      repertoire.

      NOTE:  Only one test can be performed at
      a given time.  If you send a test
      command while the modem is in test mode,
      you'll receive an ERROR message.


TESTING WITH &T

      The tests supported through the &T
      command include analog loopback, digital
      loopback and remote digital loopback.
      Users can key in their own data during
      testing, or use the modem's internal
      test pattern and error detector.

      In all cases, disable error control
      before testing.  If the modem is
      detecting errors and retransmitting the
      affected data, your results will be
      invalid.

      During testing, the MR status light
      flashes.


Ending a Test&T0, S18

      Issuing the &T0 command terminates a
      test.  Alternatively, set Register S18
      to a specified number of seconds, for
      example, S18=10.  When the 10 seconds
      are up, the modem automatically ends the
      test and returns to Command mode.  If
      the test was Analog Loopback, the &T0
      command hangs the modem up.  If the test
      was Digital or Remote Digital Loopback,
      issue an ATH command to hang up the
      modem, or an ATZ command to hang up the
      modem and reset it to its defaults.

      NOTE:  If you use the S18 test timer,
      but in the process of testing you issue
      an ATZ command, S18 resets to zero and
      the timer is disabled.  You cannot store
      a value for S18 in nonvolatile memory:
      its power-on and reset default is always
      zero.
ANALOG LOOPBACK&T1, &T8

      This test checks the operation of the
      modem's transmitter and receiver.  Data
      flow is shown in Figure F-1.










   Figure F-1.  Data Flow During Analog Loopback


      There are two analog loopback options.
      The first, &T1, involves your typing
      data that you can verify at your screen.

      The second option, &T8, is an internal
      self-test that does not involve the
      keyboard or screen.  It isolates the
      modem from the computer interface to
      give you a more specific result.

      NOTE:  HST or Dual Standard modems must
      be tested at 2400 bps or lower to avoid
      asymmetrical modulation at higher
      speeds.

   &T1

      1. If you are testing an HST or Dual
         Standard modem, set your terminal or
         software to 2400 bps.

      2. The modem must be in Command mode.
         If you wish, set Register S18 as a
         test timer, as explained earlier.
      3. Send the modem the following command.

             AT &M0 &T1 <Enter>

         The modem disables error control,
         enters analog loopback (AL) mode, and
         sends a CONNECT message.  The MR
         status light flashes.

      4. Type recognizable data so that you
         can verify it when it is looped back
         to the screen.

      5. End the test.  If you set S18, the
         modem automatically stops the test at
         the timeout, exits AL mode and
         responds OK.
         If you didn't set Register S18, wait
         one second and type +++ to bring the
         modem back to Command mode.  If DIP
         switch 9 is UP, the modem also hangs
         up and ends the test.

         If DIP switch 9 is DOWN, type AT&T0
         to end the test.  Or send either ATH
         or the command that resets the modem,
         ATZ.  The latter two commands end the
         test and hang up the modem.  The
         modem responds OK.  If the modem
         sends an ERROR message, you have
         issued an invalid command.

      6. If there were no errors, reset the
         modem to &M4, for error control,
         unless you've issued the ATZ reset
         command.

         NOTE:  If the modem is in online-
         command mode, that is, still
         connected to a remote modem, and you
         send it an &T1 or &T8 command, it
         drops the call, enters AL mode, sends
         a CONNECT result and waits for
         loopback characters.

   &T8

      This AL option causes the modem to send
      an internal test pattern to its
      transmitter and loop it back to the
      receiver.  An internal error detector
      counts any errors and, when the test is
      ended, sends the number of errors or 000
      (no errors) to the screen.

      Since you don't type anything during
      this test, and the modem does not send
      anything to the screen, this option
      verifies only the modem.  If there are
      no errors but your problem continues, it
      may be at the computer interface.

      1. If you are testing an HST or Dual
         Standard modem, set your terminal or
         software to 2400 bps.

      2. The modem must be in Command mode.
         If you wish, set Register S18 as a
         test timer, as explained earlier.

      3. Send the modem the following command:

             AT &M0 &T8 <Enter>

         The modem disables error control and
         enters AL mode.  The MR status light
         flashes.  The modem sends its
         internal test pattern to the trans-
         mitter, and loops the pattern back to
         the receiver.  You will not see any
         data on your screen.

      4. End the test.  If you set S18, the
         modem automatically stops the test at
         the timeout.  If you didn't set
         Register S18, type AT&T0 to end the
         test.  Or use ATH or the command that
         resets the modem, ATZ.  Both of the
         latter end the test and hang up the
         modem.

         The modem hangs up and returns a
         three-digit code, followed by OK.  A
         code of 000 indicates no errors were
         found.  A code of 255 indicates 255
         or more errors.  An ERROR message
         indicates that you issued an invalid
         command.

      5. If there were no errors, reset the
         modem to &M4 for error control unless
         you issued the ATZ command.

&T2

      This option is reserved.


DIGITAL LOOPBACK&T3

      If your modem has passed the AL test,
      this test can help you locate a problem
      with a remote modem or the telephone
      channel.  Figure F-2 shows the data flow
      during DL testing.

      

      

      

      

      

Figure F-2.  Data Flow During Digital Loopback


      NOTE:  This test requires the modem to
      establish a connection and return to
      online-command mode in response to the
      +++ escape code.  DIP switch 9 must be
      set DOWN so that the modem does not hang
      up on receipt of the escape code.  After
      you change the switch, issue ATZ to the
      modem to initiate the new setting.

      As with AL testing, HST and Dual
      Standard modems should be tested at 2400
      bps or lower.

      1. Set the modem to &M0, to disable
         error control.   HST and Dual
         Standard modems should be set to 2400
         bps or lower to avoid asymmetrical
         modulation at higher speeds.
         Establish a connection with the
         remote modem.

      2. Bring the modem back to Command mode
         with the +++ escape code.  Then send
         it the AT&T3 command.  The modem
         enters DL mode and the MR status
         light flashes.

      3. The remote user should type a short
         message.  It will be looped back by
         your modem's transmitter for
         verification on the remote screen.
         You will not see the message or any
         other data.

      4. When the remote user has completed
         the test,  issue the AT&T0 command to
         end the test.  Or send either ATH or
         the command that resets the modem,
         ATZ.  The latter two commands end the
         test and hang up the modem.  The
         modem responds OK.  If the modem
         sends an ERROR message, you have
         issued an invalid command.

      5. Reset DIP switch 9 UP if you normally
         use the factory default.  Reset the
         modem to &M4 unless you used the
         reset command, ATZ.


&T4, &T5

      The &T4 option causes the modem to grant
      a remote modem's request for a Remote
      Digital Loopback test.

      The &T5 option cancels &T4, and the
      modem fails to recognize such a request.
      This is the default so that your modem
      isn't subject to another user calling
      and tying up your modem without your
      permission.


REMOTE DIGITAL LOOPBACK&T6, &T7

      This test, like the local digital
      loopback test, verifies the condition of
      both modems and the phone link.  Data
      flow is shown in Figure F-3.

      

      

      

      

      

 Figure F-3.  Data Flow During Remote Digital
                   Loopback


      The request for and granting of Remote
      Digital Loopback testing requires that
      both modems use CCITT V.22 standard
      signaling.  The test must be performed
      at 2400 bps or lower.  If the remote
      modem does not have the capability or is
      not set to respond, you will get an
      ERROR result code.

      As with Analog Loopback, there are two
      Remote Digital Loopback options.  If you
      select &T6, you send keyboard data to
      the modem and verify it when it is
      returned over the phone lines and to
      your screen.  If you select &T7, the
      modem sends its internal test pattern
      and returns an error count to your
      screen.

      NOTE:  Both test options require the
      modem to establish a connection and
      return to online-command mode in
      response to the +++ escape code.  DIP
      switch 9 must be set DOWN so that the
      modem does not hang up on receipt of the
      escape code.  If necessary, set the
      switch DOWN and then issue the ATZ
      command to the modem to initiate the new
      switch setting.

   &T6

      1. Set the software to 2400 bps or
         lower.  Set the modem to &M0.  If you
         wish, set the S18 timer.

         Establish a connection with the
         remote modem.  If you haven't already
         done so, arrange with the remote user
         to cooperate with your testing and,
         if necessary, set the remote modem to
         acknowledge the RDL request.  For
         example, older USRobotics high speed
         modems need to be set to S16=8.

      2. Bring the Modem back to Command mode
         with the +++ escape code.  Send it
         the AT&T6 command.  The modem enters
         RDL mode and the MR status light
         flashes.

      3. Type a short message.  It will be
         looped back to your modem by the
         remote modem and to your screen for
         verification.  (The remote user will
         not see your data.)

      4. End the test.  If you set Register
         S18 the modem automatically ends the
         test when the test timeout is
         reached.  If you didn't set S18, type
         AT&T0 to end the test.  Or send
         either ATH or the command that resets
         the modem, ATZ.  The latter two
         commands end the test and hang up the
         modem.  The modem responds OK.  If
         you issue an invalid command, the
         modem sends an ERROR message.

         Data errors indicate a problem with
         the remote modem or the phone link.
         If you have not performed analog
         loopback testing with your modem, the
         problem may also lie with your modem.

      5. Reset DIP switch 9 UP unless you
         normally set that switch DOWN, and
         issue ATZ to the modem to initiate
         the new setting.  Reset the modem to
         &M4 unless you used the reset
         command, ATZ.

   &T7

      This test option causes the modem to
      send an internal test pattern through
      the Remote Digital Loopback.  An
      internal error detector counts any
      errors and, when the test is ended,
      sends the number of errors or 000 (no
      errors) to the screen.

      You don't need to type anything during
      this test.  The modem sends only its
      final error count to your screen.

      1. Set the software to 2400 bps or
         lower.  Set the modem to &M0.  If you
         wish, set the S18 timer.

         Establish a connection with the
         remote modem.  If you haven't already
         done so, arrange with the remote user
         to cooperate with your testing and,
         if necessary, set the remote modem to
         acknowledge the RDL request.  For
         example, older USRobotics high speed
         modems need to be set to S16=8.

      2. Bring the modem back to Command mode
         with the +++ escape code.  Then send
         it the AT&T7 command.  The modem
         enters RDL mode and the MR status
         light flashes.

         The modem sends its internal test
         pattern to the remote modem, which
         loops it back to your modem.  You
         will not see the data on your screen.

      3. End the test.  If you set S18, the
         modem automatically stops the test
         when the timer times out.  If you
         didn't set Register S18, type AT&T0
         to end the test.  Or send either ATH
         or the command that resets the modem,
         ATZ.  The latter two commands end the
         test and hang up the modem.  The
         modem responds OK.  If you issue an
         invalid command, the modem sends an
         ERROR message.

         When you terminate the test, the
         modem returns a three-digit code,
         followed by OK.  A code of 000
         indicates no errors were found.  A
         code of 255 indicates 255 or more
         errors.

         If you've performed an Analog
         Loopback and know your modem is
         working properly, errors indicate a
         problem with either the phone
         connection or the remote modem.
      4. Reset DIP switch 9 UP unless you
         normally operate with it DOWN.  Issue
         an ATZ command to initiate the new
         switch setting.  Reset the modem to
         &M4 unless you've sent it the ATZ
         reset command.


TESTING WITH REGISTER S16

      Register S16 is a bit mapped register
      with the following bit functions:

      Bit Value Function
       0   1    Analog Loopback (AL)
       1   2    Dial Test
       2   4    Test Pattern
       3   8    Remote Digital Loopback (RDL)
      
      NOTE:  Earlier USRobotics modems require
      bit 3 to be enabled in order to grant
      RDL to a remote modem.  The modem now
      requires its default &T4 setting
      instead.  To perform RDL with a
      USRobotics modem that does not use the
      &T test repertoire, that modem should be
      set to S16=8 before it can grant RDL
      testing.


ANALOG LOOPBACK (AL)S16=1D

      As with the &T AL test, do not attempt
      this test under error control.  HST and
      Dual Standard modems should be tested at
      2400 bps or lower, to avoid asymmetrical
      modulation at higher speeds.

      To use the modem's Test Pattern (S16,
      bit 2) instead of typing your own data,
      see Test PatternS16=4 later in this
      appendix.
      1. To initiate testing, type
         AT&M0S16=1D.  The modem disables
         error control, enters AL mode and
         sends a CONNECT result code.  The MR
         status light flashes.

      2. Type data to the modem for the modem
         to transmit, loop to its receiver,
         and output to the screen.  An
         alternative is to use the Test
         Pattern, described later.

      3. End the test by not typing anything
         for one second, then typing three
         pluses (+++), and waiting another
         second.  This forces the modem back
         to command mode.  If DIP switch 9 is
         UP, the modem exits AL mode and
         returns to Command mode.  If DIP
         switch 9 is DOWN, the modem maintains
         the connection when it receives the
         +++ escape code.  Issue the ATH
         command to end AL mode.

      4. Reset the modem to Data mode, S16=0,
         and error control (&M4), or issue the
         ATZ (reset) command.


DIAL TESTS16=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 <Enter>), the modem continues to
      transmit that tone until you type
      another Carriage Return.

TEST PATTERNS16=4

      The test pattern can be used instead of
      your typed data during Analog Loopback
      (AL) or Remote Digital Loopback (RDL),
      using &T commands or S16.  The test
      pattern is available at all speeds.  At
      300 bps, the modem's DTE rate must be
      fixed (&B1) and the link rate fixed at
      300 bps (&N1).  At rates over 9600 bps,
      just set the modem for a fixed DTE rate
      (&B1).

      To use the test pattern during AL
      testing with S16, type the following
      command.  The test pattern is sent
      through the loopback.

             AT&M0S16=5D

      To use the test pattern during RDL
      testing with S16, type the following
      command.

             AT&M0S16=12

      To use the test pattern with the &T AL
      or RDL tests, insert the test pattern
      command, S16=4, before issuing the test
      command.  The first of the following
      commands initiates AL, the second RDL:

             ATS16=4&T1
             ATS16=4&T6
      The test pattern alone (ATS16=4) is used
      for testing equipment and the phone
      line.  When S16 is set to 4, the modem
      transmits the test pattern upon connec-
      tion with a remote modem.

   Ending Testing with the Test Pattern

      Pressing any character key cancels all
      test pattern tests and hangs up the
      modem.  If you used Register S16, be
      sure to reset Register S16 to Data mode
      when you reset the modem to its error
      control defaults, for example, ATZ or
      AT&M4S16=0.


REMOTE DIGITAL LOOPBACKS16=8

   Responding Modem

      The responding modem must be ready to
      act on the Courier's RDL request.
      USRobotics high speed modems should be
      set to &T4.  If they do not have &T
      testing capability, they should be set
      to S16=8.

   Initiating Modem

      1. If DIP switch 9 is UP, set it DOWN so
         that it does not hang up on receipt
         of the +++ escape code.  Issue an ATZ
         command to initiate the new switch
         setting.

      2. Set the software to 2400 or 1200 bps.
         The CCITT-specified RDL signals are
         defined only for connections at 2400
         or 1200 bps.
      3. Disable error control by setting the
         modem to &M0.  Then establish a
         connection with the remote modem.

      4. Bring the modem back to Command mode
         by sending it the escape code:  one
         second of no data, three pluses
         (+++), and another second of no data.

      5. When the OK result code appears, send
         the modem the following command.

               ATS16=8 O

         The modem enters RDL mode (S16=8),
         the MR status light flashes, and the
         modem goes back online (O command).
         Then it transmits the CCITT-defined
         RDL signals, causing the remote modem
         to enter RDL mode.

      6. Type any data at the keyboard.  (Or
         send the test pattern.)
      7. To end the test, send the modem the
         +++ escape code again to bring it
         back to Command mode.

      8. When the modem sends the OK result,
         reset the modem to Data mode with the
         following command.

               ATS16=0

         The modem signals the responding
         modem that RDL testing is over.
         Terminate the call as you normally
         would, and reset the modem to its
         normal error control setting, &M4 or
         &M5.

         Or, if you wish to resume data
         transmission with the remote modem,
         add the O command to the ATS16=0
         string to return the modem online.
         Keep in mind, however, that error
         control is disabled.  Because error
         control is negotiated during the con-
         nection sequence, its status cannot
         be changed until the modem is back on
         hook and in Command mode.
