Many electronic equipments such as computers, laptops, and some desktops ship with low-power versions of RS232 ports. It seems has no ability to drive port-powered devices or full length RS232 cabling. In order to fulfill this purpose, The RS232 Line Booster
is used for cable extension, amplify (Boosting Low Power Ports) and
filter data and handshaking signals. Below is the internal system diagram to determine the direction of signal flow in RS232 Line Booster Installation.
This RS232 Line Booster internal circuit diagram shows the direction of flow on each line. Connect directly the male connector toward the computer and
the female connector end should go toward a CRT, printer or any other
interface. And there is recommendation that extension cables be no
longer than 50 feet (15-25 m).
Complete your read of RS232 Line Booster Internal Circuit Diagram for Signal Flow Determination in the pdf filetype (source: bb-elec.com)