Concept and application of D-sub

09/02/2022 Admin

A D-sub consists of two or more parallel rows of pins or sockets, usually surrounded by a D-shaped metal shield that provides mechanical support, ensures proper orientation, and shields electromagnetic interference. D-sub connectors are gendered: those with pin contacts are called male connectors or plugs, and those with receptacle contacts are called female connectors or receptacles. The shield of the receptacle is tightly fixed within the shield of the plug . Panel mount connectors typically have 4-40 jackscrews to accept screws on the cable end connector cover to lock the connectors together and provide mechanical strain relief, and can be used with 3/16" (or 5mm ) hex socket to tighten. Occasionally if you want to connect to another cable end, you can find a nut on the cable end connector. When using shielded cable, the shield is connected to the entire shield of the cable. This creates a cover that covers the entire cable and connector Electrically continuous shielding of the system.


Typical application

Communication port

The most widespread application of D-sub is for RS-232 serial communications, although this connector is not mandated by the standard. RS-232 devices originally used DB25, but in many applications the less common signal was omitted, allowing DE-9 to be used. The standard specifies male connectors for terminal equipment and female connectors for modems, but there are many variations. IBM PC compatible computers tend to have male connectors on the device and female connectors on the modem. Early Apple Macintosh models used DE-9 connectors for RS-422 multidrop serial interfaces (which could operate as RS-232). Later Macintosh models switched to an 8-pin mini-DIN connector.

On PCs, 25-pin and (starting with IBM PC/AT) 9-pin plugs are used for RS-232 serial ports; 25-pin sockets are used for parallel ports (rather than Centronics ports on the printer itself, which are card is very inconvenient).

Many uninterruptible power supply units have a DE-9F connector to signal the connected computer via the RS-232 interface. These typically don't send data serially to the computer, but use handshake control lines to indicate low battery, power failure, or other conditions. This use is not standardized among manufacturers and may require special cables.






Computer video output


The 9-pin female connector on an IBM compatible personal computer may be a video display output such as MDA, Hercules, CGA or EGA (rarely VGA or other). Even though these all use the same DE9 connector, the monitors are not all interchangeable, and the monitor or video interface could be damaged if the same connector is used to connect to an incompatible device.

Later analog video (VGA and later) adapters typically replace these connectors with DE15 high-density sockets (although some early VGA devices still use DE9 connectors). DE15 connectors are similar to DE9 connectors (see above).

Many Apple Macintosh models, starting with the Macintosh II, use the DA15 socket for analog RGB video output. Earlier Apple IIgs used the same connector for the same purpose, but the pinout was not compatible. The digital (and therefore incompatible) RGB adapter for the Apple IIe also uses the DA15F. The Apple IIc uses the DA15F as an auxiliary video port, which is not RGB, but provides the signal needed to export RGB.


The complete line of D-sub connectors also includes DA15s (one row of 7 and one of 8), DC37s (one row of 18 and one of 19), and DD50s (two rows of 17 and one of 16); these are typically used for Industrial product, the 15-way version is typically used for rotary and linear encoders.



Early Macintosh and late Apple II computers used the humble 19-pin D-sub to connect external floppy drives. Atari also uses this connector on its line of 16-bit computers to connect hard drives and Atari laser printers, and it's called an ACSI (Atari Computer System Interface) port and a DMA bus port. The Commodore Amiga uses an equally unusual 23-pin version for its video output (DB23M) and port for daisy-chaining up to 3 additional external floppy drives (DB23F).


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