Null-modem cable is basically used for communication of two RS-232 "DTE" devices with each other. To create null-modem connection between the devices you need to use two computers or two serial ports of a single computer connected with null-modem cable. The both methods described above are expensive and difficult because of many reasons. The most reliable way to create null-modem connection is using of virtual serial ports emulated by virtual serial port driver and null-modem cable.
Why do you need to emulate serial ports and null-modem connection? There are few main reasons to do it. Firstly, you don`t need to have two computers connected with real null-modem cable. Secondly, there`s no need in a single PC with several free serial ports and additional multi serial port devices which are expensive and bulky. 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 virtual serial ports on a single PC and 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. In contrast to ordinary connection you do not need any additional hardware (computers, physical serial ports, cables) to perform it. Virtual null-modem allows user emulate virtual null modem connection and run the two applications simultaneously on the same computer. Moreover, it is possible to emulate real-world situations by adding some errors to the data exchange which may occur during the physical null-modem connection. Owing to its features set Virtual Null Modem can sufficiently ease the work of software developers and testers occupied in the field of industrial automation. Furthermore, the program may also be useful in the reverse engineering as well as in educational needs.

This version allows to create one virtual null modem device and use the line control register. This version doesn't allow to add data interferences to a data flow.