How is a null modem cable wired?

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.

Is a null modem cable the same as a serial cable?

The pinout of the serial connectors on both sides of the cable are exactly the same with a straight-through serial 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.

What is the null modem connection?

Null modem is a communication method to directly connect two DTEs (computer, terminal, printer, etc.) using an RS-232 serial cable. It is also used to serially connect a computer to a printer, since both are DTE, and is known as a Printer Cable.

How do you test a null modem cable?

To tell if your NI serial cable is null modem or straight though, search for its part number in NI Serial Hardware Specifications and Features and note the cable type in the description. Alternatively, you can use a handheld DMM to test continuity on the individual pins of your serial cable.

What is null modem why it is used how it is configure?

The null modem configuration is used to connect two hosts together directly. There are no modems required. See Appendix B, Modem and Null Modem Cables for a description of the null modem cables that can be used for this configuration.

What is DTE and DCE in serial interface?

DTE or DCE. There are two types of devices that can communicate over a serial interface: DCE and DTE. A DCE provides a physical connection to a network and forwards traffic. A DTE connects to a network through a DCE device.

How many wires do serial cables have?

The RS-232 Standard Although RS-232 does not specify connector configurations, two have become de facto standards: DB25 (a 25-pin connector, in which usually no more than 10 wires are used), and DB-9 (a 9-pin connector, in which usually all 9 wires are used).

Is rs232 straight through?

The RS-232 specification defines two types of serial devices, DTE and DCE. Depending on the type of device on each end of the line, you either need a straight-through or a null-modem (“crossover”) cable in order to communicate. …

What is the pinout of null modem cable?

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.

When to use RS232 DB25 null modem pinout?

RS232 DB25 NULL Modem Pinout Use when connecting two systems (e.g. PCs) via their DB25 interfaces without a modem (i.e. back-to-back). See the full signal names in the DB25 sections. If this pinout does not work for you then you could try our Signal/pin primer because you may need to SPOOF connections.

How to connect two computers with a null modem?

Null modem cable: RS232 null modem pinout and wiring. As we have seen, null-modem connections are made possible through the use of a null mode cable. This is the simplest solution to connecting the two computers.

What is the difference between a serial and null modem cable?

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.