Epson MX-80 User Manual page 47

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How Dot Matrix Printing Works

There is no empty column on the right because there are no spaces between

graphics characters, either on the side, top or bottom.

Since the gun has only 9 wires to fire at a time, graphic characters taller than 9

require 2 passes of the print head. We saw this in Chapter 2 as program line 40

printed graphics, and repeatedly during the Chapter 1 checkout printing.

A quick glance at Appendix G Part II shows that even the smallest Graphic

character (ASCII 161) requires the firing of 4 needles, 3 times. Our best (or high-

est, as they say) Graphics resolution is therefore 1 2 dots.

Our smallest Alpha/Numeric character, the period, requires only 4 dots — 2 by 2.

That makes the highest non-graphic resolution 4 dots. For a complete listing of

all our standard MX-80 characters, look at the printout from Chapter 1. It is still

hanging on your wall, isn't it?

How It All Lays Out On Paper

To get a better idea of how these and the remaining characters are distributed on

paper, type in this program:

1 0 LPRINT

C H R $ ( 2 2 2 ) ; " T " ; C H R $ ( 2 2 2 ) ; " g " ; C H R $ ( 2 2 2 )

2 0 FOR N=1 TO 4

: L P R I N T C H R $ ( 2 2 2 ) ;

: NEXT N

(Note to TRS-80 owners. If you have not installed a lower case modification kit,

you can still type the lower case "g" required in LINE 10 by pressing the SHIFT

key when typing "G". It will show on the screen as a Capital letter, but print out

as a small one, having sent ASCII 1 03 instead of 71. This is true for all the letters.

Without the modification, the SHIFT key acts just the opposite of a regular

typewriter.)

and RUN.

Figure 5-5

Figure 5-5 shows that each Graphics character took 12 vertical positions and 6

horizontal positions, maximum. The letter " T " took 7 vertical and 5 horizontal.

(If you have a magnifying glass or super-good eyeballs, take a close look at your

print-out to verify Figure 5-5.)