THE FUNDAMENTALS OF
DOT MATRIX PRINTING
Understanding dot-matrix printing and Gemini’s graphics begins with knowing some details about the print head and the software that controls it. This chapter will provide you with those details. The print head, print matrix, and vertical spacing are described in understandable terms. The second half of this chapter will introduce you to dot graphics: the control codes for firing the “pins:’and a sample graphics program that will put a smile on your paper, and perhaps on your face.
THE PRINT HEAD
The print head contains nine thin wires, or pins, positioned one above the other. Figure 6-1 illustrates the print head, from the paper’s point of view, looking straight on. Each wire is connected to a solenoid “gun;’an electromagnet that “fires” when told to do so by the “computer” inside Gemini. Figure 6-2 presents a schematic of the print-head mechanism, profiling the solenoid, spring, and dot-wire pin for one of the guns.
| Needle of | il |
| print head | |
Upw | n | 3 |
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Lower B==
7-bit interface
O-bitInterface
Figure 6-1. The bit-image column-scan capability is the result of nine pins, stacked in a column, each “fired” independently in response to signals from the 7-bit or a-bit interface from your computer.
