232NM2395 - pg. 1/1
1993 B&B Electronics - Revised June 1993
NULL MODEMS
Document No. 232NM2395
Null Modems are used to interconnect two computers with similar RS-232 ports. If
both ports are DTE or both DCE you cannot connect them directly together. You need a
Null Modem to cross pins 2 and 3 (TD and RD) and to loop back the handshake lines. The
following diagrams show the four main null modem adapters.
PDF 
ZIP