Chapter 4
Each pin is driven by a “gun,” or electromagnet, which “fires” when told to do so by the electronics inside the printer. The printer electronics responds to those ASCII code instructions we send from the computer in the form of “ASCII numbers.”
For example, to print the letter “I.” wires 1 and 7 are fired first. They hit the ribbon, which makes marks on the paper where the left top and bottom of the letter “I” should be.
The head then shifts over a bit and wires 1,2,3,4,5,6 and 7 all fire at once, printing the center of the letter “I.” One more shift and one more shot of needles 1 and 7 and the letter “I” is complete. (Figure
Figure
This is called “dot matrix” printing. Dots are printed according to a pre- designed “matrix” or “grid” system, where each letter, number, and punctuation mark is formed by an arrangement of dots. As we have seen, this complex printing process takes place very quickly.
The pins fire only in groups or clusters. The firing patterns are already programmed inside the printer, matching the alphanumerics (letters and numbers) and symbols found in our ASCII charts. No, we cannot fire an individual needle yet, but that’s what all this is leading up to.
Appendix C shows all our alphanumeric characters constructed within a 7 dot high by 5 dot wide matrix. Every letter, number, and punctuation character is designed to fit within that box.
Notice that the sixth column is always empty. In fact, it isn’t even shown. It’s reserved for horizontal spacing between characters.
Our smallest alphanumeric character, the period, requires only 4 dots in a 2 by 2 grid. Our highest “resolution” in the
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