TELEBYTE TECHNOLOGY, INC.
=========================

   MODEL 420

   Modem Type               Data (synchronous)                    
   Maximum Data Rate        128Kbps                               
   Data Bus                 External                              
   Data Modulation Protocol Proprietary                           

<gopher://bitreich.org/I/th99/t/S-T/51493-1.png>
   

   +------------------------------------------------------------+
   |                        CONNECTIONS                         |
   |------------------------------------------------------------|
   |      Purpose       | Location |     Purpose     | Location |
   |--------------------+----------+-----------------+----------|
   | DC power           |   CN1    | Receive         |   CN4    |
   |--------------------+----------+-----------------+----------|
   | RS-232/422         |   CN2    | Transmit        |   CN5    |
   |--------------------+----------+-----------------+----------|
   | Ground             |   CN3    |                 |          |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                         CARRIER ON                         |
   |------------------------------------------------------------|
   | Setting                       |           SW2/C            |
   |-------------------------------+----------------------------|
   |>> Always on                   |             On             |
   |-------------------------------+----------------------------|
   | RTS high                      |            Off             |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                           GROUND                           |
   |------------------------------------------------------------|
   | Setting                             |         JP1          |
   |-------------------------------------+----------------------|
   |>> Frame and signal ground connected |  Pins 1 & 2 closed   |
   |-------------------------------------+----------------------|
   | Frame and signal ground separate    |  Pins 3 & 4 closed   |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                         IMPEDANCE                          |
   |------------------------------------------------------------|
   | Setting                     |             JP2              |
   |-----------------------------+------------------------------|
   |>> 135 Ohms(low)             |      Pins 1 & 4 closed       |
   |-----------------------------+------------------------------|
   | High                        |      Pins 3 & 4 closed       |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                         LINE SPEED                         |
   |------------------------------------------------------------|
   | Speed    | SW1/A  | SW1/B  | SW1/C | SW1/D | SW1/E | SW1/F |
   |----------+--------+--------+-------+-------+-------+-------|
   | 32Kbps   |   Up   |  Down  | Down  | Down  | Down  | Down  |
   |----------+--------+--------+-------+-------+-------+-------|
   | 48Kbps   |  Down  |   Up   | Down  | Down  | Down  | Down  |
   |----------+--------+--------+-------+-------+-------+-------|
   | 56Kbps   |  Down  |  Down  |  Up   | Down  | Down  | Down  |
   |----------+--------+--------+-------+-------+-------+-------|
   |>> 64Kbps |  Down  |  Down  | Down  |  Up   | Down  | Down  |
   |----------+--------+--------+-------+-------+-------+-------|
   | 72Kbps   |  Down  |  Down  | Down  | Down  |  Up   | Down  |
   |----------+--------+--------+-------+-------+-------+-------|
   | 128Kbps  |  Down  |  Down  | Down  | Down  | Down  |  Up   |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                       RECEIVE CLOCK                        |
   |------------------------------------------------------------|
   | Setting                       |            SW/H            |
   |-------------------------------+----------------------------|
   |>> Disabled                    |            Down            |
   |-------------------------------+----------------------------|
   | Enabled                       |             Up             |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                       RTS/CTS DELAY                        |
   |------------------------------------------------------------|
   | Setting            |       SW2/A       |       SW2/B       |
   |--------------------+-------------------+-------------------|
   |>> Disabled         |        Off        |        Off        |
   |--------------------+-------------------+-------------------|
   | 7ms                |        On         |        Off        |
   |--------------------+-------------------+-------------------|
   | 60ms               |        Off        |        On         |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                   TRANSMIT CLOCK SOURCE                    |
   |------------------------------------------------------------|
   | Setting                       |           SW1/G            |
   |-------------------------------+----------------------------|
   |>> Internal                    |            Down            |
   |-------------------------------+----------------------------|
   | External                      |             Up             |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                FACTORY CONFIGURED SETTINGS                 |
   |------------------------------------------------------------|
   |           Jumper            |           Setting            |
   |-----------------------------+------------------------------|
   |            SW2/D            |           Not used           |
   +------------------------------------------------------------+

   +------------------------------------------------------------+
   |                     DIAGNOSTIC LED(S)                      |
   |------------------------------------------------------------|
   |  LED  |  Color  | Status  |           Condition            |
   |-------+---------+---------+--------------------------------|
   |  PWR  |   Red   |   On    |          Power is on           |
   |-------+---------+---------+--------------------------------|
   |  PWR  |   Red   |   Off   |          Power is off          |
   |-------+---------+---------+--------------------------------|
   |  TD   |   Red   |   On    |   Modem is transmitting data   |
   |-------+---------+---------+--------------------------------|
   |  TD   |   Red   |   Off   | Modem is not transmitting data |
   |-------+---------+---------+--------------------------------|
   |  RD   |   Red   |   On    |    Modem is receiving data     |
   |-------+---------+---------+--------------------------------|
   |  RD   |   Red   |   Off   |  Modem is not receiving data   |
   |-------+---------+---------+--------------------------------|
   |  RTS  |   Red   |   On    |       RTS signal is high       |
   |-------+---------+---------+--------------------------------|
   |  RTS  |   Red   |   Off   |       RTS signal is low        |
   |-------+---------+---------+--------------------------------|
   |  DCD  |   Red   |   On    |    Carrier signal detected     |
   |-------+---------+---------+--------------------------------|
   |  DCD  |   Red   |   Off   |  Carrier signal not detected   |
   |-------+---------+---------+--------------------------------|
   |  TM   |   Red   |   On    |     Modem is in test mode      |
   |-------+---------+---------+--------------------------------|
   |  TM   |   Red   |   Off   |     Modem is in test mode      |
   +------------------------------------------------------------+