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Dot patterns
The Apex80’s print head is able to print graphics in addition to text
because graphic images are formed on the Apex80 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 Apex80 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 Apex80 can, therefore, be
as finely detailed as the one on the first page of this chapter.
In its main graphics mode the Apex80 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
Apex80 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.
Introduction to Dot Graphics
6.3