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Null modem overview

 

The purpose of a null-modem cable is to permit two RS-232 "DTE" devices to communicate with each other without modems or other communication devices (i.e., "DCE"s) between them.

 

To achieve this, the most obvious connection is that the TD signal of one device must be connected to the RD input of the other device (and vice versa). Also, however, many DTE devices use other RS-232 pins for out-of-band (i.e., "hardware") flow control. One of the most common schemes is for the DTE (the PC) to assert the RTS signal if it is ready to receive data (yes, it DOES sound backwards, but that's how it works), and for the DCE (the modem) to assert CTS when it is able to accept data. By connecting the RTS pin of one DTE to the CTS pin of the other DTE, we can simulate this handshake.

 

Also, it is common convention for many DTE devices to assert the DTR signal when they are powered on, and for many DCE devices to assert the DSR signal when they are powered on, and to assert the CD signal when they are connected. By connecting the DTR signal of one DTE to both the CD and DSR inputs of the other DTE (and vice versa), we are able to trick each DTE into thinking that it is connected to a DCE that is powered up and online.

 

Software overview

 

Virtual Null Modem (VNM) is an utility, which purpose is to emulate one or more RS232 serial ports connected via virtual null-modem cable. Otherwise, you can create any number of pure virtual serial ports in your system (COM10, COM11, COM255 etc), that will be connected to each other via virtual null-modem cable.

 

If you have two applications you want to connect to each other using serial ports you need a null modem. A null modem is bascially a cable to connect two serial ports to each other. Normally you need two computers or two physical ports on one computer to achive this. Using Virtual Null Modem software you can emulate the null modem and run the two applications on the same computer without any additional hardware.

 

Example:

 

You can create two virtual serial ports: COM10 and COM12 and connect two different applications to them. Everything, that application #1 will send to COM10 will be received by application #2 at COM12, and all that application #2 sends to COM12 will be received by application #1 at COM10.

 

 

Features:

 

No reboot required. Creating, installing and removing of virtual serial ports occurs at real time;
You can create any number of virtual serial ports pairs;
Any other hardware or virtual serial ports are not used or occupied;
You even can have no serial ports in your system;
Other applications will never see the difference between real serial port and virtual serial ports, created by Virtual Null Modem software;
The link between two virtual serial ports is faster then real null-modem cable connection and depends on your computer system speed;
The virtual link is much more reliable than common physical link;
Virtual Null Modem uses kernel driver technology and supports: WDM, WMI, Power Management, PNP, etc.;
Virtual Null Modem software has a simple, menu-driven step by step set-up. Programming is not required to configure the software to configure virtual serial ports and virtual serial ports pairs;
If you are software developer, then you can configure each port to sumulate a real-world data exchange with errors in data;
You can add, remove virtual null modems from your application by using a command line interface.

 

 

DISCLAIMER:

We take no responsibility for any damage or injury caused by files written or edited with this software.

 

As the user has twenty one days to try this software with the full function demo version, warranty is limited to replacement of defective product.

 

For more information, to report bugs, or to make suggestions please see our website at www.aggsoft.com, or email support@aggsoft.com.

 

 Company home page: http://www.aggsoft.com/

 Software home page: http://www.virtual-null-modem.com/

 Serial port hardware reference: http://www.aggsoft.com/rs232-pinout-cable/




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