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Dot patterns
The EXs print head is able to print graphics in addition to text
because graphic images are formed on the EX about 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 EX also forms its images with
patterns of dots, as many as 240 dot positions per inch horizontally and
72 dots vertically The images printed by the EX can, therefore, be as
finely detailed as the one on the first page of this chapter.
In its main graphics mode the EX prints one column of dots for each
code it receives, and it uses only the top eight of the nine pins.
Therefore, your graphics program must send codes for dot patterns, one
number for each column in a line. For each of those columns the print
head prints the pattern of dots you have specified.
To print figures taller than eight dots, the print head makes more than
one pass. The printer prints one line, then advances the paper and
prints another, just as it does with text.
To keep the print head from leaving gaps between the graphics lines
as it does between the text lines, the line spacing must be changed to
eliminate the space between lines. With a change in line spacing, the
EX can print finely detailed graphic images that give no indication that
they are made up of separate lines, each no more than 8/72nds of an
inch tall.
Each pass of the print head prints one piece of the total pattern,
which can be as tall or short and as wide or narrow as you desire. You
don’t have to fill the whole page or even an entire line with your
graphics figures. In fact, you can use as little or as much space as you
like for a figure and put it anywhere on the page.
Pin Labels
The graphics mode requires a method to tell the printer which pins to
fire in each column. Since there are 256 possible combinations of eight
pins, you need a numbering system that allows you to use a single
number to specify which of the 256 possible patterns you want. This
numbering system is shown in Figure 6-1 on the next page.
Graphics and Userdefined Characters
6-3