Elements Of Dot-Matrix Printing And Computer / Printer Communications; The Print Head - Epson Printer Interface Cartridge for the Apple IIc Operation Manual

Elements of Dot-Matrix Printing
and Computer / Printer Communications
This chapter is for those of you who want to know something about
how your printer works. It's a simple, non-technical explanation of
the basics of dot-matrix printing that will help you understand some
of the later chapters, particularly the ones on user-defined characters
and graphics.

The Print Head

The LX-90 uses a print head with nine pins or wires mounted verti-
cally. Each time a pin is fired, it strikes the inked ribbon and presses it
against the paper to produce a dot. This dot is about l/72nd of an inch
in diameter. (The size varies slightly. depending upon the age of the
ribbon and the type of paper used.) As the head moves horizontally
across the page, these pins are fired time after time in different patterns
to produce letters, numbers, symbols, or graphics.
For example, to print a pica capital T (shown in Figure 3-l), the
head fires the top pin, moves 1/60th of an inch, fires the top pin again,
moves 1/60th of an inch, fires the top pin and the six below it at the
same time, moves 1/60th of an inch, fires the top pin, moves another
1/60th of an inch, and fires the top pin once more to finish the letter.
All this happens in only l/lOOth of a second.
Chapter 3
Figure 3-7. A capital T
15