Chapter 17: Printers^435
USB-to-parallel adapter cable that has a Centronics connector on the printer
end and a USB connector on the PC end.
IR (infrared) or IrDA (Infrared Data Association) There are adapters available
that can be used to connect a parallel printer to a PC through its IrDA connection,
like the one made by Extended Systems (www.extendedsystems.com). This frees
the parallel port on the PC for other uses. A number of handheld-size printers are
available for use with notebooks and PDAs with an IrDA connection.Parallel cables have distance limitations. Older Centronics cables should not be more
than 15 feet in length; between 9 feet and 12 feet is best. Newer IEEE-1284 cables can ex-
tend u pto 30 feet in length, and there are some 50-foot high-end cables available as well.
Typically, if you need to be more than 10 feet away from a printer, you would connect
into a network.Using a Switchbox
You can use a switchbox, either manual or automatic, to connect more than one nonlaser
printer or any other parallel device or devices to a single parallel port. You can also use
them to allow multiple PCs to share a single printer. A dial designates which PC or device
is to be connected to the primary device of the switchbox. Switchboxes are also called
A/BswitchesbecausethedevicesattachedarelabeledasA,B,C,andsoon.Anautomatic
switchbox senses activity on a line and automatically switches to that line.
In general, a laser printer should not be connected to a switchbox, especially newer laser
printers. Laser printers are highly interactive with the printer and have very high voltage re-
quirements. There is also the issue of electrical noise. Taking the laser printer on- and offline
by changing the active location, either manually or automatically, can interrupt device driver
commands and create electrical noise spikes that could possibly damage the laser printer or
the PC’s parallel port.Printer Standards
In 1984, the IEEE (Institute of Electrical and Electronics Engineers) standardized parallel
port protocols. The standard has a very long name but is commonly known as IEEE 1284.
This standard incorporates the two legacy parallel port standards with a new protocol.
The standards included in IEEE 1284 are as follows: Standard parallel port (SPP) This parallel standard allows data to travel
in only one direction—from the computer to the printer.
Enhanced Parallel Port (EPP) This parallel standard allows data to flow
in both directions, but only one way at a time. An EPP connection allows
the printer to communicate with the processor to signal out of paper, open
cover, and other conditions.