74 Delta User’s Manual ._
Dot Matrix Printing In order to create download characters, you’ll need some
understanding of how dot matrix printers work. They’re called
“dot matrix” because each character is made up of a group of
dots. Look closely at some printed characters produced by your
Delta and vou will see the dots. Figure 7-l shows how the letter
“A” is formed by printing 17 dots. -
Figure 7-1. The letter “A” is created by pnntlng 17 dots.
The printhead in Delta consists of nine thin wires stacked one
atop the other. Figure 7-2 shows an enlarged schematic view of
the front of the printhead, showing the ends of the wires and their
relationship to the printed characters. As you can see, the capital
letters use the top seven wires of the printhead, and the descen-
ders (such as the lower case “g” shown) use the bottom seven
pins. As the printhead moves across the page (in either direction- -
that’s what is meant by bi-directional printing) it prints one col-
umn of dots at a time. Each time a dot is supposed to print an
electromagnet inside the printhead causes the appropriate wire to
strike the ribbon (making Delta an impact printer).
The Print Matrix All of the standard characters that Delta prints are formed
from patterns of dots that are permanently stored in the printer’s
ROM (read-only memory). This includes all of the standard ASCII
characters, the block graphics and special characters, the interna-
tional character sets, and the italic characters.
But there is another area of memory in Delta reserved for
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