The Centronics interface is a standard input/output (I/O) interface designed in the 1970s for connecting printers and other devices. It was developed by the Centronics printer company which is now defunct. The Centronics interface, also known as a Parallel Port, became the standard means of connecting printers to personal computers for decades.The technology that the Centronics interface developed into included a number of incarnations of the Parallel interface including the ECP (Entended Capabilities Parallel) and EPP (Enhanced Parallel Port) versions. The technology required a 25 way connector of which up to 17 wires were used in the specification and bi-directional communications became possible in the enhanced versions like ECP and EPP.Today, the Centronics interface has been largely replaced by the universal serial bus (USB). For the most part, many manufactures have entirely omitted the parallel interface. However, a USB-to-parallel port adapter is available for PCs without a parallel port. These can be used for parallel printers and other peripheral devices that have a parallel interface. The Centronics interface is also known as a the Centronics port, parallel port or printer port.
The first parallel port for printers was the Centronics Model 101, which transmitted data eight bits at a time. Later, parallel ports became bidirectional and were used for printers and input devices The original Centronics Model 101 was cost effective and very advanced for its time. It had a print speed of 125 characters per second and weighed 155 pounds.The interface used a Centronics parallel port, but an RS-232 serial port was optional. In the original Centronics interface, data flowed in one direction only but used eight parallel data lines which was a technological advance of the day. Serial communications were sent down in sequence so in theory the parallel port was eight times faster, although in reality the speed was about triple at most.When the IEEE 1284 standard was introduced in 1994, the logic voltages, length of cables and the interface were all standardized. The IEEE 1284's five standard were specified to support data transfer in the forward direction, backward direction, or bi-directionally. The five modes of operation are:
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