Null modem, also called crossover, is a term associated with serial RS cables. A standard serial cable, also called an AT cable, has the wires inside the cable running straight through.
What is Modem explain? A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves.
A modem converts between these two forms. What is rs port? The RS standard had been commonly used in computer serial ports and is still widely used in industrial communication devices.
What is a serial crossover cable? A null modem serial cable frequently called a crossover cable is used to connect two DTE devices together without the use of a DCE device in between. Do modems give off WiFi? The modem provides access to the Internet, and the router broadcasts a WiFi signal, allowing your devices to connect to each other and the Internet.
A WiFi-capable device can then use this signal to connect to the Internet. Routers are available from many different manufacturers. What type of hand shake method is used to transfer data down the cable? TLS handshake This protocol is used to exchange all the information required by both sides for the exchange of the actual application data by TLS.
It defines the messages formatting or containing this information and the order of their exchange. What is DTE in networking? Short for Data Terminal Equipment, a device that controls data flowing to or from a computer. The term is most often used in reference to serial communications defined by the RSC standard. A standard serial cable, also called an AT cable , has the wires inside the cable running straight through.
Take a DB9 cable as an example. Pin 1 on one end of the cable would be connected to Pin 1 on the other end. Then Pin 2 to 2, 3 to 3, and so on. Null modem cables are serial cables that use an alternative pinout for different functionality. Originally, all serial cables were AT cables and could not connect two devices such as two computers directly.
They required a modem or similar equipment as a go-between. Null modem cables changed that old standard, allowing devices to be linked up directly with no middleman equipment. This allows older computers and other machines with serial ports to transfer data between each other directly, similar to more modern ethernet crossover cables.
Null modem cables work by switching around wire pairs when going from one end of the cable to the other. Returning to the DB9 example, a null modem cable would have Pin 2 on one side connected to Pin 3 on the other side. Then Pin 4 would be connected to Pin 6 and Pin 7 to Pin 8. Pins 1 and 9 are unused while Pin 5 still connects to itself, acting as the ground wire.
This type of null modem cable is called a Handshake cable. The way these cables are wired allows two connected devices to talk and listen to each other at the same time. Standard AT cables attempt to do the same thing cannot due to their straight-thru pinout.
While there are a few different types of handshake cables , the chart below shows the most common version and is the only type available as a stock item today. With serial cables now considered obsolete, the odds of running into one of the other types is practically non-existent unless you happen to be using very old, very specific equipment. A standard pinout featuring the two most common null modem cables, DB9 and DB They are also used by computer gamers to directly connect their machines together for more fluid gameplay.
The length of a null modem cable is limited to 30 feet, so physical proximity is necessary to use an RS null modem. It uses the same pinout structure on each end of the cable and is what you commonly use to connect your computer to an external device with a serial port. Straight through serial cables can be longer than a null modem serial cable with lengths up to 50 meters. Performance degrades as the length increases, so the two pieces of equipment need to be located fairly close together.
Straight through cables can be turned into null modems by the use of a null modem adapter. These adapters cross the data transmission lines of the straight serial cable emulating null modem connections. Use of a null modem adapter adds flexibility to your serial cable. As previously mentioned, using a null modem means having the two pieces of equipment close together. You may not be able to achieve this accessibility nor want to have extra cables cluttering the area.
There is a simple software solution available to solve these issues. Null Modem Emulator by Electronic Team can create compatible serial ports that are connected by a virtual null modem. This virtual null modem application creates ports that appear the same as hardware ports to your operating system or any Windows application.
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