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Dot patterns
The LQ-2500 prints graphics the same way that pictures in
newspapers and magazines are printed. If you look closely at a
newspaper photograph, you can see that it is made up of many small
dots. The LQ also forms its images with patterns of dots, as many as
360 dot positions per inch horizontally and 180 dots vertically The
images printed by the LQ can, therefore, be as finely detailed as the one
on the first page of this chapter.
Eight-pin graphics
The LQ has an eight-pin graphics mode with six densities, so that it is
compatible with the many programs written for printers such as the
Epson FX and RX series. Although this mode uses only one third of the
LQ’s pins, it produces good quality graphics and allows you to use the
many programs written for eight-pin graphics.
Twenty-four-pin graphics
The 24-pin graphics mode takes full advantage of the LQ’s print head.
It has five densities, but for simplicity this explanation covers only
triple-density
Triple-density prints up to 180 dots per inch horizontally As the print
head moves across the paper, every 1/180th of an inch it must receive
instructions about which of its 24 pins to fire. At each position it can fire
any number of pins from none to 24. This means that the printer must
receive 24 bits of information for each column it prints. Since the LQ
uses eight-bit bytes of information in its communication with a
computer, it needs three bytes of information for each position.
Pin labels
The graphics mode requires a method to tell the printer which pins to
fire in each column. The software must send codes for the dot patterns;
one number is needed for each column in a line. For each of those
columns the print head prints the pattern of dots you have specified.
There are 256 possible combinations of eight pins, so a single
number in the range O-255 can be used to specify which of the patterns
you want. In this system, one number is assigned to each pin as in
Figure 6-1, on the following page.
Graphics and User- defined Characters
6-3