If you need to make your own null modem cable follow this wiring diagram for the 3 wire null modem cable method.
Make a null modem cable.
This means lugging around a null modem cable in addition to the non standard rj 45 to db 9 console cable required by most cisco equipment.
The cable is comprised of three lines.
If you are making a straight extension cable not a null modem cable just stay on the same side of the table.
A null modem or crossover cable is used to connect to dte devices together.
When using an adapter make sure to only put a null modem adapter on one end.
For this to work the transmit txd pin of one device needs to be connected to the receive rxd pin of the other device and vice versa.
As we already know a null modem connection is based on a null modem cable which offers the easiest path to connect two machines together.
Null modem communication refers to using a crossed over rs 232 cable to connect the teleprinters directly to one.
One wire is the signal ground the second one is the receiving line and the third one is the transmitting wire.
This is the simplest solution to connecting the two computers.
The adapters change the pin.
Null modem cables are still somewhat common today having been used on many machines for a few decades.
It s much easier than most others.
But what is a null modem cable.
Transmit data to receive data in both directions that s two of the pins and ground to ground.
For example to make a 9 to 25 straight cable wire the 9 pin plug according to the leftmost column and the 25 pin plug according to the second column from the left.
But after putting together four simple custom adapters i now have an ethernet cable a crossover ethernet cable a modem cable a null modem cable and a cisco console cable all by carrying around just one.
Null modem is a communication method to directly connect two dtes computer terminal printer etc using an rs 232 serial cable the name stems from the historical use of rs 232 cables to connect two teleprinter devices or two modems in order to communicate with one another.
As we have seen null modem connections are made possible through the use of a null mode cable.
Along with full fledged cables there are also null modem adapters that can be used to change a straight thru cable into null modem.
Simple null modem cable.
A null modem cable rs 232 serial cable is used when one needs to connect a dte data terminal equipment to another via their communication ports.
Despite these warnings this type of null modem cable has been used successfully between windows 95 98 me computers with a direct cable connection.
This simple solution includes three lines.
When such a cable is employed to establish a connection between two dtes both the dtes are made to believe that they are connected through modems.
Rs232 null modem pinout and wiring.
Therefore although this null modem cable is cheap and easy to make use it with care.
Null modem with partial handshaking.
Null modem cable with handshake.
