This page 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 ImageStream router). 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)