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45
w ASCII codes and the CHR$ function
You can talk to your computer
in BASIC, but your computer
and your printer talk to each other in what are known as ASCII
codes. In the ASCII code, each number from 0 to 255 has a par-
ticular meaning
- 36, for example, makes the printer print a
dollar sign. Some numbers cause the printer to do other things,
too. For instance, sending a 7 sounds the printer's bell.
Taken together,
these numbers and their meanings make up
the ASCII code (pronounced
ask-key), which stands
for the
American Standard Code for Information Interchange. There are
ASCII codes for all the letters of the alphabet (upper case and
lower case), 0 to 9, most punctuation
marks, and some (but not
all) of the functions of the printer.
There are a number of different ways to represent
an ASCII
code, depending
on how you are using it. For example,
the
ASCII codes for the upper-case
letter "A" are 65 (decimal) or
&H41 (hexadecimal).
Or you can just call it "A". Appendix
C
shows all of the ASCII codes.
BASIC
uses
the
CHR$
function
to
represent
ASCII
characters
and many functions.
To print the letter "A" we
would enter LPRINT
CHR$(65). To make the printer's
bell
sound, we would enter LPRINT CHR$(7). In general, we print a
character
by entering
LPRINT
CHR$(ASCII
code) to the
printer.
We can also use hex ASCII codes. Although
we use only
decimal ASCII codes in this manual, in some applications
it will
help if you understand
what a hex code is. "Hex" is short for hex-
adecimal and refers to a base-16 number (the numbers we use in
everyday life are base 10). Since the hex system needs 16 digits,
it uses the numerals 0 through 9 and also the letters A through
F. In BASIC programs,
you can always tell that a number is in
hexadecimal by the "&H" immediately
preceding it. The ASCII
code for the letter "A" (65 in decimal) is &H41 in hex.
n Control codes
ASCII codes with values of 32 or less do not correspond
to
keys on the keyboard. These codes control many of the printer's
functions, so we call them control codes. To enter a control code
from the keyboard, we have to press two keys at the same time
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