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need to know to use your printer as a regular printer. But this
printer
isn't just a regular
printer.
Your printer
has many
capabilities that your commercial
software isn't aware of. A lit-
tle later we will see what it takes to use some of your printer's
advanced features with commercial
software.
n
First, some terminology
Your printer knows what to print because it knows how to in-
terpret the codes that the computer sends to it. These codes are
numbers that the computer sends to your printer. Both the com-
puter and the printer know the meaning of these codes because
they are a set of standard
codes used by almost all microcom-
puters. This set of codes is the American Standard Code
for
Infor-
mation Interchange,
which is usually referred to as ASCII (pro-
nounced ask-key). There are ASCII codes for all the letters of the
alphabet, both lower case and capital, the numbers from 0 to 9,
most punctuation
marks, and some (but not all) of the printer's
functions.
ASCII codes are referred
to in several different
ways, de-
pending on the way they are used. Sometimes
these codes are
treated
as regular
numbers.
For example,
the letter
"A" is
represented
by the number 65 in ASCII. Appendix B shows all
of the ASCII codes.
In BASIC, ASCII codes are used in the CHR$ function. This
function is used to print the character that is represented
by the
number
in the CHR$(
) function.
The
BASIC
statement
PRINT CHR$(65) will print an "A" on the terminal.
In some other programming
languages, ASCII codes are refer-
red to by their hex value. "Hex" is short for hexadecimal which is
a base-16 number
system
(our usual numbers
are base-lo).
Since hex needs 16 digits, it uses the numbers 0 through 9 and
then it uses the letters A through F for digits. The ASCII code
for the letter "A" is 41 in hex.
Of course, most of the time we don't even need to think about
this code system. Our computers
are smart enough to know that
when we press the "A" key on our keyboard we want to print
the letter "A". The computer
takes care of all the rest.
But there are a number of ASCII codes that don't have keys
on the keyboard.
The most important
of these codes are the
codes that ASCII values below 32. These codes control many of
this printer's functions. Even though there aren't keys for these
codes, most keyboards
can send these
codes.
It's done by
holding down the "control" key (many times marked CTRL) and
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