Virtual Null Modem 2.0.2.25 descriptions To emulate null-modem connection Virtual Null Modem can be effectively used. The program emulates one or more couples of RS-232 serial ports connected via virtual null-modem cable. It is possible to create the unlimited couples of VSP on a single PC without additional hardware & connect them in any sequence using virtual null-modem cable. Usually you need to use virtual null-modem when you have two applications to be connected via serial ports.