DB-25

DB-25. It is a member of the D-subminiature family of electrical connectors, originally developed by ITT Cannon in the 1950s. Characterized by its distinctive D-shaped metal shield, the connector features two rows of pins totaling 25 contacts. It became one of the most ubiquitous interfaces for serial communication and parallel port connections throughout the latter half of the 20th century.

Overview

The DB-25 connector was standardized as part of the RS-232 interface, a specification created by the Electronic Industries Alliance. Its design provided a robust and reliable connection for data transmission between Data Terminal Equipment and Data Circuit-terminating Equipment, such as between a computer and an external modem. The connector's prevalence was cemented by its adoption on early personal computers from manufacturers like IBM for their parallel port implementations, most notably for connecting printers such as the IBM Proprinter. Its use extended beyond computing into various industrial and telecommunications equipment, making it a fundamental component in the infrastructure of the Digital Revolution.

Physical and electrical characteristics

Physically, the DB-25 connector consists of a D-subminiature shell that houses 25 pins arranged in two staggered rows, with 13 pins on one row and 12 on the other. The shell, typically made of steel or zinc alloy, provides EMI shielding and ensures proper polarization to prevent incorrect mating. Electrically, the connector was designed for relatively low-speed, asynchronous serial communication as defined by the RS-232 standard, which specified signal voltages typically in the range of ±3 to ±15 volts. The standard did not define a maximum data rate, but practical limitations of the interface and typical cabling often restricted reliable operation to speeds below 20 kbit/s in early implementations, though later hardware pushed this higher.

Common applications

Its most famous application was as the standard connector for RS-232 serial ports on computers and peripherals throughout the 1970s, 80s, and 90s, used for connecting modems, computer terminals, and mice. A second major use was as the connector for the Centronics-compatible parallel printer port on IBM PC compatible computers, facilitating communication with devices like the Epson FX series. In professional audio, a DB-25 connector is commonly used in TASCAM's TDIF format for multi-channel digital audio interfacing. It also found extensive use in SCSI-1 implementations and for connecting specific peripherals on older Sun Microsystems and Silicon Graphics workstations.

Pin assignments

For classic RS-232 serial communication on a Data Terminal Equipment device, key pin assignments include Pin 2 for Transmitted Data, Pin 3 for Received Data, and Pin 7 for Signal Ground. Handshaking signals used pins like Request to Send on Pin 4 and Clear to Send on Pin 5. When used as a parallel port, the assignments were completely different and defined by the IEEE 1284 standard; for example, Pins 2 through 9 were used for the eight data bits. The TDIF protocol repurposes the connector for eight channels of digital audio in and out. These varied assignments highlight the connector's flexibility, though they also led to potential confusion and incompatibility between different cable types.

Variants and related connectors

Several related connectors exist within the same family. The DE-9 connector, with 9 pins, became the standard for RS-232 on later IBM PCs and is familiar from joystick ports on the Atari 2600 and Commodore 64. The DA-15 is a 15-pin version used for game controller ports and older Ethernet transceivers. High-density versions, like the HD15 used for VGA video output, feature three rows of pins within the same shell size. The DB-25 itself was also produced in solder cup, printed circuit board mount, and IDC connector styles. While largely supplanted by modern interfaces like USB, HDMI, and DisplayPort, the DB-25 and its relatives remain in use in legacy industrial, audio, and aerospace systems.

Category:Computer connectors Category:Electrical connectors Category:Serial buses