DTE-DCE Interface Cont

™   NULL MODEM o    Suppose you need to connect two DTEs in the same building, for example two workstations o    Modems are not needed to connect two compatible devices directly o    The  TX  never  needs  to  cross  analog  lines,  such  as  telephone  lines  and therefore does not need to be modulated o    But you do need an interface to handle the exchanging , just as EIA 232 DTE- DCE cable does o    The solution is a NULL Modem o    A null modem provide DTA -DTE interface w/o DCEs o    But why use a Null Modem o    If all you need is the interface, why not just a a standard EIA 232 cable? o    Part a shows a connection using a telephone network o    Part b shows what happens when we use the same connections between two DTEs o    The receive circuit is void because it has been isolated completely for the TX o    The tx cct 2 endsup full of collision noise NULL MODEM Crossing Connections o    Whereas  EIA  232  DTE-DCE  interface  cable  has  a  female  connector  at  the DTE  and  a  male  connector  at  the  DCE  end,  a  null  modem  has  female connectors at both ends to allow it to connect to the EIA 232 DTE ports which a male