D-subminiature
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The D-subminiature or D-sub is a common type of electrical connector used particularly in computers. Calling them "subminiature" was appropriate when they were first introduced, but today they are among the largest common connectors used in computers.
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[edit] Description and nomenclature
A D-sub contains two or more parallel rows of pins or sockets usually surrounded by a D-shaped metal shield that provides mechanical support and some 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 ITT Cannon , part of ITT Corporation in 1952.[1] 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. The pins in these connectors are spaced approximately 0.108 inch (2.74 mm) apart with the rows spaced 0.112 inch (2.84 mm) apart.
Cannon also produced D-subs with larger positions in place of some of the normal pin positions that could be used for either high-current or co-axial inserts. 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 below, the connector on the left is a 9-pin plug (DE9M), and the one on the right is a 25-pin 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 jackscrews on the cable shell, to hold the plug and socket together.
Possibly because the original PC used DB25 connectors for the serial and parallel ports, many people, not knowing the significance of the letter "B" as the shell size, began to call all D-sub connectors "DB" connectors instead of specifying "DA," "DC" or "DE." When the PC serial port began to use 9 pin connectors, they were often called "DB9" instead of DE9. It is now common to see DE9 connectors sold as "DB9" connectors.
There are now D-sub connectors which have the original shell sizes, but more pins, and the names follow the same pattern. For example, the DE15, usually found in VGA cables, has 15 pins in a shell the same size as a DE9. The full list of connectors with this pin spacing is: DE15, DA26, DB44, DC62, and DD78. Alternatively, following the same confusion mentioned above in which all D-sub connectors are called "DB", these connectors are often called DB15HD, DB26HD, DB44HD, DC62HD, and DD78HD, where the "HD" stands for "high density". They all have 3 rows of pins, except the DD78, which has 4.
A series of D-sub connectors with even denser pins is called "double density", and consists of DE19, DA31, DB52, DC79, and DD100. They have 4 rows of pins.
There is yet another similar family of connectors that is easy to confuse with the D-sub family, but is not part of it. These connectors are named like "HD50" and "HD68", and have a D-shaped shell but the shell is about half the width of a DB25. They are common in SCSI attachments.
The original D-subminiature connectors are now defined by an international standard, DIN 41652.
[edit] Typical applications
The widest application of D-subs is for RS-232 serial communications, though the standard did not make this connector mandatory. RS-232 devices originally used the DB25 25-pin D-sub, but for many applications the less common signals were omitted, allowing a DE9 9-pin D-sub to be used.
On PCs, 9-pin and 25-pin plugs are used for the RS-232 (serial) ports and 25-pin sockets are used for the (parallel) printer ports (instead of the Centronics socket found on the printer itself). All of these are now being superseded by USB and other standards.
A male DE9 connector on the back of an IBM-PC-compatible computer is typically a serial port connector. IBM introduced the DE9 connector for RS-232 on PCs with the Personal Computer AT in 1984. A female 9-pin connector on the same computer may be a video display output: monochrome, CGA, or EGA. Even though these all use the same connector, the displays cannot all be interchanged and monitors or video interfaces may even be damaged if connected to an incompatible device using the same connector. Later analog video (VGA and later) adapters replaced these connectors by DE15 15-pin high-density sockets, which have three rows of five contacts each in the space that was previously occupied by two rows of five and four contacts. Other common names for DE15 connectors are HD15, where HD stands for High Density, and (less accurately) DB15 and DB15HD.
From the late 1970s and all through the '80s, DE9s 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, Amiga, 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. DE9 connectors are also used for some token ring and other computer networks. DA15 is used for Ethernet Attachment Unit Interface.
Many uninterruptible power supply units have a DE9F connector on them, in order to signal an attached computer that the mains (utility) electricity is off (or back on), or that the battery is low. Many of these actually do not use true serial communication as the consumer might be led to believe, but rather other signaling wires present on a serial port. Compatibility of signaling protocols or wiring of the supplied DE9 cable also differs between manufacturers of UPS units, thus a "power restored" signal from one UPS might be interpreted as a "shutdown" signal by the software. Some manufacturers deliberately wire the DE9 connector improperly in order to defeat competition, and force customers to use proprietary rather than generic cables.
The complete range of D-sub connectors also includes 15-pin DA15s (two rows of 7 and 8); 37-pin DC37s (two rows of 18 and 19); and 50-pin DD50s (two rows of 17 and one of 16), the last two being used in industrial products. The 15-pin DA15 has been notably used for color video output on early Macintosh computers and as the IBM-defined analogue joystick port on PCs (where it is female). Many third-party PC sound cards, particularly the Sound Blaster line from Creative Labs, included a variation of the IBM joystick port using the same connector but taking two of the pins to add a (usually MPU-401 compatible) MIDI interface. The DA15F was also used for the AUI connectors included on Ethernet cards in the 1980s and 1990s, albeit with a sliding latch to lock the connectors together instead of the usual hex studs with threaded holes. Finally, the early Macintosh and Apple II line of computers used a very rare 19 pin D-sub for connecting to external floppy disk drives, and the Commodore Amiga used an unusual 23-pin version for both its video output and for connecting an external floppy drive.
[edit] Multi-channel audio
TASCAM used DB25 connectors for their multi-track recording equipment (TDIF), and Logitek Audio later did the same for its broadcast consoles, though with different pinouts. Logitek's pinout is far more straightforward, going across each row: 1-2-3, 4-5-6, 7-8-9, 10-11-12; then 14-15-16, 17-18-19, 20-21-22, 23-24-25. Nominally, stereo pairs would use adjacent pins on opposite rows (i.e. 1-2-3 left and 14-15-16 right), but these are completely reassignable in NVRAM via software. TASCAM's pinout goes channel-backward from right to left, and skips back and forth between each row. [1] (On both types, the indicated pin numbers are positive-negative-ground, channels 1 to 8.) A few patch panels have been made which have the DB25 connectors on the back with phone jacks (or even TT jacks) on the front, however these are normally wired for TASCAM, which is more common outside of broadcasting.
[edit] Types and variants
D-sub connectors exist in at least four types, differentiated by the method used to attach wires to the contacts. These are solder-cup or solder-bucket, insulation displacement, crimp, and PCB pins. Solder-bucket contacts have a cavity into which the stripped wire is inserted and hand-soldered (a somewhat tricky process especially to do alone as the wire can easily pop out of the bucket whilst soldering unless held there). Insulation displacement contacts (IDC) 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. This is a very quick means of assembly whether done by hand or automatically but requires use of flat ribbon cable which can be awkward to handle and makes it difficult to make cables with different connections at each end. 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. PCB pins as the name suggests are intended to be soldered direct to a printed circuit board and not to a wire. These connectors are usually mounted at a right-angle to the PCB allowing a cable to be plugged into the edge of the PCB assembly. Blocks containing multiple stacked D connectors (and sometimes other connectors too) are nearly always seen on ATX (or variants thereof) PC motherboards but aren't generally seen elsewhere.
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.
[edit] Decline in Usage
The D-Sub connector family is now in decline for general usage, for several reasons: cost, size, and lack of flexibility. For portable devices such as MP3 players or mobile phones, the D-sub connector is usually too large to physically fit. Many laptop computers, where weight and size are crucial, no longer include D-subs. Even small form factor PCs may find D-sub connectors too large for their value.
Because of the relatively complex shapes and assembly, especially the shaped metal D shield, and screws and nuts for physical securing, D-sub connectors are now quite expensive compared to other common connectors, which are mostly simpler. In the retail PC world where margins are very thin, these connectors are a natural target for removal.
Finally the D-sub connector is somewhat inflexible. The large number of pins is no longer useful and therefore usually wasteful. The port does not provide any defined pin for power, eliminating it from reliable use for unpowered expansion devices, although some devices such as RS-232 to RS-422 converters attempt to power themselves from signal lines. The physical design is not friendly to plug-and-play applications.
For video purposes, the DE15HD connector is being slowly replaced by DVI and HDMI connectors, although this transition is proceeding more slowly, since many analog CRT monitors are still in use and the digital DVI connector is not useful for those.
For the majority of other consumer applications, D-sub serial and parallel connectors have been replaced by USB or Ethernet connections.
[edit] Notes and references
- ^ Are D Subs from all manufactures compatible? — reply in the FAQ section of the Cannon company web
[edit] External links
| Audio and video connectors |
|---|
| Single conductor: Binding post | Banana plug | Fahnestock clip |
| Audio: RCA | Jack plug | XLR | DIN / Mini-DIN | BNC | DB25 | Speakon | TosLink |
| Video: DVI / Mini-DVI / UDI | RCA | VGA / Mini-VGA | DFP | BNC | DIN / Mini-DIN | 13W3 | D-Terminal | DisplayPort |
| Multi: ADC | P&D | HDMI | TRS | SCART | F | Belling-Lee | DisplayPort |
