Other Interface Standards

Other Interface Standards o    Both Data Rate and Cable LENGTH are restricted by EIA 232 o    Data rate to 20 Kbps and Cable length to 50 feet o    To  meet  need  of  users  requiring  more  speed  or  distance  ,  the  EIA  and  ITU-T  has introduces additional standards: EIA 49, EIA 530 and X.21 ™   EIA 449 o    Mechanical  specifications  of  EIA  448  define  a  combination  of  two  connectors  ,  on with 37 pins ( DB 37) and one with 9 pins (DB 9) for a combined 46 pins o    The  functional  specifications  of  EIA  449  give  the  DB  37  pins  properties  similar  to those of the DB 25. o    The  major  functional  difference  b/w  25  and  37  pin  connectors  is  that  all  functions relating to the secondary channel have been removed from DB 37 o    Because the secondary channel is seldom used, EIA 449 separates those functions out and puts them in the second, 9 pin connector (DB9) o    In this way, a second channel is available to systems that need it    EIA 449 (PINS) o    To  maintain  compatibility  with  EIA  232,  EIA  449  defines  two  categories  of pins to be used in exchanging data, control, and timing information    Category 1 pins    Category 2 pns    Category 1 and 2 pins Category  1  includes  those  pins  whose functions are  compatible  with  EIA 232 Category 2 pins are those that have no equivalent in EIA 232 or have been redefined DB9  connector here is different from the one that is previously discussed    Electrical Specifications RS423, RS 422 EIA 449 uses two standards to define its electrical specifications: •     RS-423: Unbalanced Mode •     RS-422: Balanced Mode •     RS 423 Unbalanced Mode o    Unbalanced Circuit Specification o    Unbalanced means that it defines only one line for propagating a signal o    All  signals  in  this  standard  use  a  common  return  or  a  ground  to complete the circuit