In modern systems, such a cable can still be useful for kernel mode development, since it allows the user to remotely debug a kernel with a minimum of device drivers and code (a serial driver mainly consists of two FIFO buffers and an interrupt service routine). The popularity and availability of faster information exchange systems such as Ethernet made the use of null modem cables less common. On the Commodore Amiga system, a null modem connection was a common way of playing multiplayer games between two machines. No Ethernet hardware (such as a network interface card or a modem) is required for this. Both pieces of software allow the mapping of a hard disk on one computer as a network drive on the other computer. The later versions of MS-DOS were shipped with the InterLnk program. Under the Microsoft Windows operating system, the direct cable connection can be used over a null modem connection. Null modems were commonly used for file transfer between computers, or remote operation. When an application required that two DTEs (or two DCEs) needed to communicate with each other, then a null modem was necessary. As the RS-232 standard was adopted by other types of equipment, designers needed to decide whether their devices would have DTE-like or DCE-like interfaces. The original application of a null modem was to connect two teleprinter terminals directly without using modems. two PCs) providing full handshaking, which works with software relying on proper assertion of the Data Carrier Detect (DCD) signal: One side Null modem cables were a popular method for transferring data between the early personal computers from the 1980s to the early 1990s.īelow is a very common wiring diagram for a null modem cable to interconnect two DTEs (e.g. The term null modem may also refer to the cable or adapter itself as well as the connection method. If a user wished to connect two teleprinters directly without modems (null modem) then they would crosslink the connections. Each teleprinter would be physically connected to its modem via an RS-232 connection and the modems could call each other to establish a remote connection between the teleprinters. Originally, the RS-232 standard was developed and used for teleprinter machines which could communicate with each other over phone lines.

What is rs232 cable