Table of Contents
Advertisement
36
Where did that noise come from? That's the printer's bell. We
will learn more about it in Chapter
5. We just wanted
to il-
lustrate a code that causes the printer to perform a function.
n The escape codes
Back when the ASCII system was set up, computer
equip-
ment was relatively simple and thirty-three
control codes were
considered
sufficient
at
the
time.
The
American
Standards
people realized that, eventually,
more control codes
would be needed
so they included
the escape (ESC) code to
allow almost any number of additional codes to be defined when
they became necessary.
ESC allows us to "escape" from the ordinary set of control
codes so we can specify additional functions and other informa-
tion needed for a printer function. In this manual, we'll write the
ESC code inside broken brackets,
like this - (ESC).
(ESC) - decimal 27 - is always followed by at least one
other number; it is never used alone. The whole series of related
numbers is called an escape sequence.
n A note on command syntax
Because the readers
of this manual will be running
such a
wide variety of applications
on so many different computers,
we
just can't show the exact way of sending codes to the printer for
each one of them. Instead, as we introduce you to each new com-
mand, we will show the commands
as in this example:
(ESC)
"W"
1
This command that turns on expanded printing. (ESC), as we
mentioned
earlier, is the escape code (which is ASCII code 27).
A letter or number in quotes (such as the "W" above) means that
the character should be sent to the printer (without the quotes).
In our example,
you should send a capital W following
the
escape code. In BASIC, you could do this in a couple of ways: by
sending the character itself (e.g. LPRINT "W";), or by using the
CHR$ function to send the ASCII code for the character
(e.g.
LPRINT
CHR$(87);).
Many of printer commands
end with a 1 or 0. When shown as
in the above example (i.e. no quotes and no "CHR$"), you can
use either ASCII code 1 (i.e. CHR$(l)) or the character
"1"
(which is ASCII code 49). The same idea applies to commands
Advertisement
Table of Contents
