Permalink
Switch branches/tags
Nothing to show
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
29 lines (13 sloc) 2.26 KB

What is a null modem cable?

A null-modem is a connection between two serial devices accomplished by using a specially designed null modem cable. These serial devices are usually computers and are connected through their RS-232 communication ports.

The RS-232 protocol was designed to be used to connect a telephone modem and a teletype machine. Teletypes could communicate with each other through the modems. This means that that the RS-232 connection is asymmetric, requiring a modem on one end and the data source or consumer on the other end.

In an RS-232 null modem connection, transmission and reception lines are crosswise connected, allowing two way data traffic. Null-modem connections are not standardized, leading to multiple RS232 null modem pinout possibilities.

Currently, null modem connections are used primarily to enable data transmission between older computers and laptops that do not have a USB port or network card. In these situations, a null-modem cable is the only way to allow data transmission.

Null modem cable

Learn more about null modem connection and null modem pinout and wiring

Virtual Null Modem Emulation

As previously stated, null-modem connections are not able to provide high-speed data transfer. The maximum speed of data transmission through a COM port is 115 kb/s. This speed is often reduced in practice as the length of the null-modem cable directly affects the transmission speed.

By using a Null Modem Emulator, also known as a virtual null modem, you can increase your data exchange rate and make it more efficient. This virtual null modem software connects COM ports by way of a virtual null modem cable. Virtual serial port pairs created with Virtual COM Port Driver transmit data so that serial data sent to one COM port is immediately available in the other port. Using a virtual null modem emulator allows this data transmission to be two-way between the COM pairs.

Virtual Null Modem Emulator