From Academic Kids

The D-subminiature or D-sub is a common type of electrical connector used particularly in computers (that is, a computer connector). Calling them "subminiature" was appropriate when they were first introduced, but today they are among the largest common connectors used in computers.


Description and nomenclature

D-sub connectors. Left: . Right: .
D-sub connectors. Left: DE9M. Right: DB25F.

A D-sub contains two or more parallel rows of pins or sockets usually surrounded by a D-shaped metal shield that provides screening against electromagnetic interference. The D shape guarantees correct orientation. The part containing pin contacts is called the male connector or plug, while that containing socket contacts is called the female connector or socket. The socket's shield fits tightly inside the plug's shield. The shields are connected to the overall screens of the cables (when screened cables are used), creating an electrically continuous screen covering the whole cable and connector system.

D-subminiature connectors were invented by Cannon, part of ITT. Cannon's part-numbering system uses a D as the prefix for the whole series, followed by a letter denoting the shell size (A=15 pin, B=25 pin, C=37 pin, D=50 pin, E=9 pin), followed by the actual number of pins, followed by the gender (M=male, F=female). For example, DB25M denotes a D-sub with a 25-pin shell size and 25 male contacts. Cannon also produce D-subs with high-current or co-axial inserts that replace several of the normal, smaller pins. The DB13W3 variant was commonly used for high-performance video connections; this variant provided 10 regular (#20) pins plus three coaxial contacts for the red, green, and blue video signals.

In the photograph above, the connector on the left is a 9-way plug (DE9M), and the one on the right is a 25-way socket (DB25F). The hexagonal pillars at either end of each connector have a threaded stud (not visible) that passes through flanges on the connector, fastening it to the metal panel. They also have a threaded hole that receives the jack screws on the cable shell, to hold the plug and socket together.

Possibly because the original PC used DB-25 connectors for the serial and parallel ports, it seems that many people, not knowing the significance of the letter B as the shell size, began to call all connectors of this sort "DB" connectors instead of "D" connectors. When the PC serial port began to use 9 pin connectors, they were often called "DB-9" instead of DE-9. It is now common to see DE-9 connectors sold as "DB" connectors.

The connectors are now defined by an international standard, DIN 41652.

Typical applications

The widest application of D-subs is in RS-232 serial communications, although the standard recommended but did not make mandatory the common D-subs connectors. RS-232 links originally used the DB25 25-way D-sub, but for many applications the less common signals were omitted, enabling a DE9 9-way D-sub to be used.

On PCs, 9-way and 25-way plugs are used for the RS-232 (serial) ports and 25-way sockets are used for the Centronics (parallel) printer ports (instead of the same style of socket as found on the printer itself), though all of these are now being superseded by PS/2 miniature DIN connectors and USB ports.

A male DE-9 connector on the back of an IBM-PC compatible computer is typically a serial port connector. A female 9-pin connector on the same computer may be for a monochrome, or CGA, or EGA, video output. Even though these all use the same connector, the displays cannot be interchanged and monitors may even be damaged if connected to an incompatible video card using the same connector. Later, for analogue video (VGA and later) these connectors were replaced by DE15 15-way high-density sockets, which have three rows of five contacts in the same space that was previously occupied by two rows, one of five contacts and another of four.

DE-9 connectors are also used for some token ring networks, joysticks, and for a myriad of other electronics uses.

From the late 1970s and all through the 80s, DE9M's without the pair of fastening screws were almost universal as game controller connectors on video game consoles and home computers, after being made a de facto standard by the use of such game ports in the Atari 2600 game console and the Atari 8-bit family of computers. Computer systems which use them include Atari, Commodore, Amstrad, and SEGA systems, among others, but exclude Apple and PC systems and most newer game consoles. Used in the standard way, they support one digital joystick and one pair of analog paddles; on many systems a computer mouse or a light pen is also supported through these sockets, however mice are not usually exchangeable between different systems.

The complete range of D-sub connectors also includes 15-way (DA15; two rows of 7 and 8) used for color video output on early Macintosh computers and for analogue joysticks on PCs; 37-way (DC37; two rows of 18 and 19); and 50-way (DD50; two rows of 17 and one of 16), the last two being used in industrial products.

Types and variants

D-sub connectors exist in at least three types, differentiated by the method used to attach wires to the contacts. These are solder-bucket, insulation displacement, and crimp. Solder-bucket contacts have a cavity into which the stripped wire is inserted and hand-soldered. Insulation displacement contacts (IDC) are designed for automated assembly and allow a ribbon cable to be forced onto sharp tines on the back of the contacts; this action pierces the insulation of all the wires simultaneously. Crimp contacts are assembled by inserting a stripped wire end into a cavity in the rear of the contact, then crushing the cavity using a crimp tool causing it to grip the wire tightly at many points. The crimped contact is then inserted into the connector where it locks into place. Individual crimped pins can be removed later with a tool inserted into the rear of the connector. This "rear release" feature is valuable when pins are damaged or modifications must be made to the circuits.

A smaller type of connector derived from the D-subminiature, and about half the linear size, is called the microminiature D, or micro-D, which is a trademark of ITT Cannon. This connector is used in industrial instrumentation products. A few manufacturers make nano-D connectors, which are about half the size again.

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