The text that you are reading now is printed in portrait
mode. In landscape mode, the page is rotated 90
degrees and the data is printed across the length of the
page. Using standard paper, portrait mode is aligned
8.5 inches wide × 11 inches long; in landscape mode the
paper is aligned 11 inches wide × 8.5 inches long.
Orientation is selectable on some dot matrix
printers, ink jet printers, and all laser printers.
TOPIC 2BASIC PRINTER
All printers have the same function, that is to print
data on paper.
The method they use to put the
information on paper varies with the type of printer.
This section covers areas of the printer that are common
to most printers: interface, control, paper feed, and
All printers need to communicate with the host
computer. Communications is handled in the interface
section. Printers connected to mainframe computers
generally have a communications protocol that is
designed for the computer, such as NTDS fast or NTDS
slow interface. Smaller printers used with personal
computers will have either serial or parallel interfaces.
The most widely accepted serial interface is
Recommended Standard-232 or simply RS-232. The
most widely used parallel interface is the Centronics
standard parallel interface.
RS-232 Serial Interface
RS-232 was developed by the Electronics Industry
Association (EIA) to be a universal serial interface
standard for any serial device such as a modem, printer,
For a printer to properly receive serial data, the
parallel bytes that the computer works with must be
converted into a serial data string. Once the data string
is received by the printer, it must be reconverted to
parallel data for the printer to use. These conversions
are accomplished by a special circuit called a universal
asynchronous receiver/transmitter (UART). The
UART can perform both parallel to serial and serial to
parallel inversions. UARTs do not need extra control
lines to control the flow of data, so the UART never
knows when a new character is arriving. To send a data
word, the UART must attach from two to four extra bits.
First, the UART inserts a binary ZERO to represent a
start bit. The next seven or eight bits represent the
actual data code. Although some printers still work
with seven data bits, eight bits is the standard found on
most printers today. After the data code is sent, the
parity of the data is checked and a parity bit maybe
added. Whether a printer uses even or odd parity is
determined by the manufacturer and is set up when the
printer is connected to a computer. To end the data
word, the UART adds one or two stop bits. Configuring
the UART for a printer is accomplished by setting a
number of dip switches of the circuit board.
The RS-232 interface cable is connected to the
computer and printer by a DB-25 sub-miniature
connector. The DB-25 connector is a 25-pin D-type
connector. Although the connector has 25-pins, serial
communications with software handshaking needs as
few as three of the pins connected.
Handshaking signals are signals that control the
printer. Software handshaking uses the ASCII codes
such as XON/XOFF and ETX/ACK. Hardware
handshaking uses an additional line to indicate data
terminal ready (DTR) to the computers data set
ready (DSR) pin. When hardware handshaking is used,
the printer cannot send data to the computer.
Centronics Parallel Interface
The Centronics parallel interface uses a 36-pin
Centronics connector at the printer end of the cable and
a DB-25 subminiature connector at the computer. The
parallel interface is an eight-bit, two-way interface
between the computer and the printer. When the
computer sends data to the computer, it places the data
on the data lines and sets a strobe signal. The strobe
signal indicates to the printer that the data is ready for
transfer. When the printer samples the data, it will set
the acknowledge line to tell the computer it has sampled
The control section of a printer directs all printer
This section receives and decodes
computer data from the interface section. If the data
contains characters to be printed, the control section
determines what character it is and when to activate the
print mechanism. The print mechanism can be a print
hammer, a series of print wires, a laser beam, or some
other mechanism. The control section receives signals
from various parts of the printer as to the presence of
paper, carriage position, and print head temperature.