Centronics Connectors

Centronics connectors are standard parallel interface devices for connecting printers and other peripherals such as portable disc drives, tape backup drives, and CD-ROM players to computers. Centronics connectors are named after the printer that first used them and include two rows of flat contacts. Both male and female Centronics connectors are available. Male Centronics connectors have side latches that snap into tabs on the sides of female connectors. Female connectors also have slots to receive pins from male connectors. Typically, Centronics connections consist of a 36-pin male or female connector at the printer or other peripheral, a cable, and a 25-pin parallel port on the computer. Centronics connectors use eight parallel data lines, as well as other lines to read status information and send control signals.

The first Centronics connectors transmitted data in only one direction, from a computer, and to only one type of device, a printer. With the development of new peripherals, the Institute of Electrical and Electronics Engineers (IEEC) approved and expanded the communications standard for Centronics connectors. IEEE 1284 specifies five modes of operation: compatibility, nibble, bite, enhanced capability port (ECP), and enhanced parallel port (EPP). Compatibility mode, the original Centronics parallel interface, is intended for use with dot matrix and older laser printers, but can be combined with nibble mode for bi-directional transfer. As its name suggests, nibble mode sends data back to the computer in two 4-bit nibbles. By contrast, byte mode transfers a single byte of data from the peripheral to the computer. ECP, an advanced bi-directional mode used by scanners and faxes, incorporates channel addressing. EPP uses data cycles that transfer data between the computer and the peripheral and address cycles that assign address, channel, or command information.

Selecting Centronics connectors requires an analysis of several product specifications Devices differ in terms of gender, the number of contacts, contact resistance, insulation resistance, plating, housing, and mounting.  Contact resistance is the measurement of electrical resistance of mated contacts when assembled in a connector under typical service use. Insulation resistance is the electric resistance between two conductors separated by an insulating material. Typically, Centronics connectors are plated with copper, gold, nickel, or silver. Housing is usually constructed of metal or plastic. Basic geometries include straight and right angle connectors. Some Centronics connectors attach directly to printed circuit boards (PCBs) through pre-drilled holes. Others incorporate surface mount technology (SMT) or use receptacle mounting, typically when panel cutouts are required. Dummy receptacles store cable assembly connector plugs.

There are a variety of applications for Centronics connectors. Some connectors work only with peripherals that support the IEEE 1284 standard. Others are designed for use with devices that use the small computer systems interface (SCSI). Micro connectors and nano connectors exhibit contacts with a pitch of 0.05” and 0.025'', respectively. Peripherals that do not use Centronics connectors often use universal serial bus (USB) or Bayonet Neil-Concelman (BNC) connectors instead.