DTE to DTE (Null Modem) August 13,1999 SUMMARY: This Technote provides information for connecting two asynchronous serial (RS-232) Data Terminal Equipment (DTE) devices together (example: two PC's or a dumb terminal and a Lucent PortMaster (TM) product). Assuming both DTEs have DB-25 interfaces, each DTE transmits data on pin 2 and receives data on pin 3. Consequently, both DTE devices cannot transmit or receive data on the same pin.  A straight thru cable does not allow data to be transmitted or received.  Therefore, a null modem cable is required to allow both ends to transmit and receive data.  PIN OUTS: pin 1  (GND) goes to pin 1  (GND) pin 2  (TD)  goes to pin 3  (RD) pin 3  (RD)  goes to pin 2  (TD) pin 4  (RTS) goes to pin 5  (CTS) pin 5  (CTS) goes to pin 4  (RTS) pin 6  (DSR) goes to pin 6  (DSR) pin 7  (GND) goes to pin 7  (GND) pin 8  (DCD) goes to pin 20 (DTR) pin 20 (DTR) goes to pin 8  (DCD) TIPS: Null modem cables and cable adapters  may be purchased from any retailer handling computer products and supplies or computer games.   The minimum number of pin outs for a null modem cable for a basic configuration is illustrated below:          pin 2 (TD)  goes to pin 3 (RD)       pin 3 (RD)  goes to pin 2 (TD)       pin 7 (GND) goes to pin 7 (GND)