Specifications

■ Laser scanning
■ Toner application
■ Toner fusing
Various printers perform these procedures in various ways, but the steps are fundamentally the same.
Less expensive printers, for example, might rely on the PC to perform more of the processing tasks,
whereas others have the internal hardware to do the processing themselves.
Communications
The first step in the printing process is to get the print job data from the PC to the printer. PCs tradi-
tionally use the parallel port to communicate with a printer, although many printers can use a serial
port. Some devices can even use both types of ports at the same time to connect to two computers.
Network printers often bypass these ports entirely and use an internal Ethernet adapter to connect
directly to the network cable. The newest SOHO and office printers offer USB connections, either as
their only port or along with a parallel port.
Communications between the printer and the PC obviously consist largely of print job data sent from
the computer to the printer. However, communications flow in the other direction, as well. The
printer also sends signals back to the PC for the purpose of flow control—that is, to inform the com-
puter when to stop sending data and when to resume. These signals also can indicate error condi-
tions, such as paper out. The printer typically has an internal memory buffer that is smaller than the
average print job and can handle only certain amount of data at a time. As pages are actually printed,
the printer purges data from its buffer and signals the PC to continue transmitting. This is commonly
called handshaking. The handshaking protocols used for this communication depend on the port used
to connect the printer to the PC.
The amount of data a printer can hold varies widely, and you read earlier in this chapter how you
often can enlarge the buffer by installing additional memory. Some printers even contain internal
hard disk drives and can store large amounts of print data and collections of fonts. The process of
temporarily storing multiple print jobs as they await processing is known as print spooling. Spooling
can also take place in the computer or on the network, using the client PC or the print server’s hard
drive to store print jobs.
Almost all printers today support even more advanced communications with a PC, enabling a user to
interrogate the printer for its current status using a software application and even to configure para-
meters that previously were accessible only from the control panel on the printer. This type of com-
munication requires that the PC have a bidirectional, an ECP, or an EPP port and the appropriate
cable IEEE-1284 parallel cable or be connected via the USB port. If the printer is shared through a
switchbox, the extension cables and switchbox must also be IEEE-1284 compliant. Bidirectional
modes enable the printer to transmit more advanced status information, such as ink levels, toner
levels, and error messages.
Note
If you are not getting ink or toner level messages or other status reports from a parallel printer that is supposed to provide
this information, check the following:
■ Make sure that EPP or ECP support (check printer documentation for which to use) is enabled in the port setup.
On most systems, the parallel port is controlled through the system BIOS. Restart your computer and enter the
system BIOS to verify that the correct setting is present.