What makes a null modem cable?
A null modem cable is a RS-232 serial cable where the transmit and receive lines are crosslinked. In some cables there are also handshake lines crosslinked. In many situations a straight-through serial cable is used, together with a null modem adapter. The adapter contains the necessary crosslinks between the signals.
How do I make a null modem?
How To Make a Null Modem Cable
- Verify that you need a null modem cable.
- Determine what kind of plugs you will need.
- Purchase some multi-conductor cable with at least seven conductors, and the appropriate female DB9 and/or DB25 connectors.
- Refer to the table below for pin assignments.
What type of cable is most commonly used to terminate a serial connection to a modem?
What type of cable is most commonly used to terminate a serial connection to a modem? A DB-9 is usually used to terminate a RS-232 connection on a serial cable.
What makes a null modem a null cable?
Null modem cables are serial cables that use an alternative pinout for different functionality. A standard DB9 AT cable pinout (non-null modem) 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.
Do you need a null modem for a DB9 cable?
A standard DB9 AT cable pinout (non-null modem) 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.
How is a null modem used in DTE?
A Null Modem or “crossover” cable is used to connect to DTE devices together. 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.
What’s the difference between DCE and null modem?
Crossover or “Null Modem” vs. Straight Through Serial Cable. DTE normally refers to the serial port on a PC or terminal, while DCE refers to a modem or other type of communications device. 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.