CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [386]
IEEE 1284 Standard
In 1991, a group of printer manufacturers proposed to the Institute of Electrical and Electronics Engineers (IEEE) that a committee be formed to propose a standard for a backward-compatible, high-speed, bidirectional parallel port for the PC. The committee was the IEEE 1284 committee (hence the name of the standard).
The IEEE 1284 standard requires the following:
Support for five distinct modes of operation: compatibility mode, nibble mode, byte mode, EPP, and ECP
A standard method of negotiation for determining which modes are supported both by the host PC and by the peripheral device
A standard physical interface (that is, the cables and connectors)
A standard electrical interface (that is, termination, impedance, and so on)
Because only one set of data wires exists, all data transfer modes included in the IEEE 1284 standard are half-duplex: Data is transferred in only one direction at a time.
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NOTE The five modes of operation for parallel printing specified in the IEEE 1284 standard (compatibility, nibble, byte, EPP, ECP) are inching closer to obsolescence as USB printers take over the market. If you find yourself needing to optimize the performance of a legacy parallel printer, you can look up these modes by name, using various Web search tools.
Parallel Connections, Cabling, and Electricity
Although no true standard exists, standard parallel cable usually refers to a printer cable with the previously mentioned male DB-25 connector on one end and a 36-pin Centronics connector on the other (Figure 22-11). The shielding (or lack thereof) of the internal wiring and other electrical characteristics of a standard parallel printer cable are largely undefined except by custom. In practice, these standard cables are acceptable for transferring data at 150 KBps, and for distances of less than 6 feet, but they would be dangerously unreliable for some transfer modes.
Figure 22-11 Standard parallel cable with 36-pin Centronics connector on one end and DB-25 connector on the other
For more reliability at distances up to 32 feet (10 meters), use proper IEEE 1284-compliant cabling. The transfer speed drops with the longer cables, but it does work, and sometimes the trade-off between speed and distance is worth it.
Installing a parallel cable is a snap. Just insert the DB-25 connector into the parallel port on the back of the PC and insert the Centronics connector into the printer’s Centronics port, and you’re ready to go to press!
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NOTE Some printers come with both USB and parallel connections, but this has become very rare. If you need a parallel printer for a system, be sure to confirm that the particular model you want will work with your system!
USB Printers
New printers now use USB connections that you can plug into any USB port on your computer. USB printers don’t usually come with a USB cable, so you need to purchase one when you purchase a printer. (It’s quite a disappointment to come home with your new printer only to find you can’t connect it because it didn’t come with a USB cable.) Most printers use the standard USB type A connector on one end and the smaller USB type B connector on the other end, although some use two type A connectors. Whichever configuration your USB printer has, just plug in the USB cable—it’s literally that easy!
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NOTE In almost all cases, you must install drivers before you plug a USB printer into your computer. You’ll learn about installing printer drivers later in this chapter.
FireWire Printers
Some printers offer FireWire connections in addition to or instead of USB connections. A FireWire printer is just as easy to connect as a USB printer, because FireWire is also hot-swappable and hot-pluggable. Again, make sure you have the proper cable, as most printers don’t come with one. If your printer has both connections, which one should you use? The answer is easy if your PC has only