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:

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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