Null Modem pin connetion for both 25 and 9 pin RS-232 connectors
One connector is assembled from each side of the hyphens. The frame ground on the 25 pin plug is optional and should only be connected on one side of the cable. If you need Data Carrier Detect (DCD) on your cable (BBS programs, Unix Getty and so on) then: On a 25 pin plug connect pin 6 and 8. On a 9 pin plug connect pin 1 and 6. The connections for DCD should be made on the same end of the cable.
http://www.loop-back.com/null-mod.html
