How the program works
This program begins by assigning a number of printer commands to BASIC
string variables (lines 1000 to 1070). You can find most of these commands
near the beginning of chapter 4.
The WIDTH “LPTl:” 255 statement in line 1090 means infinite line width.
It prevents the IBM-PC from inserting unwanted carriage returns and line
feeds in graphics data.
Actual printing begins in line 1100. Using the preassigned commands, the
program prints samples of its different fonts, followed by samples of the
print pitches, then some double and quadruple-sized printing.
Next comes the central attraction of the program: a line of text printed
fourteen times in expanding and contracting loops to give a barrel effect. The
work is done by four printer commands: a command setting the right margin
(line 1370); a centering command (line 1390); a command to vary the line
spacing (lines 1410 and 1460); and a command to micro-adjust the space
between characters (lines 1420 and 1470).
Next the program returns to normal spacing and gives a demonstration of the
printer’s word-processing abilities: italic printing, bold printing, underlin-
ing, subscripts, etc.
The row of automobiles in the next printed line is created by downloading
two new character patterns, which are printed in place of the character “<“
(character 60). Details can be found in Chapter 5.
The final part of the program uses dot graphics to print some “SW” logos
with various densities. The dot pattern of the logo was originally laid out on
graph paper, then converted to the data in lines 2370 to 2630 with the help
of a calculator. Each number represents eight vertical dots. (See “Graphics
commands” in Chapter 4 for details.)
The pattern is printed in four rows, each eight dots high and 65 dots wide.
Lines 1800 to 1870 read the dot data into a string array variable named
LOGO$. Line 1880 sets the line spacing to 8/72 inch so that the rows will
connect vertically. The loop in lines 1890 to 1990 does the printing in four
passes of the print head.
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