 If it is necessary to connect two DTE devices (or two DCE devices but that is more unusual), a cross-over null modem, in the form of either an adapter or a cable, must be used.Generally, serial port connectors are gendered, only allowing connectors to mate with a connector of the opposite gender.With D-subminiature connectors, the male connectors have protruding pins, and female connectors have corresponding round sockets.