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for user-defined
characters,
but a caution is in order. Characters
with ASCII values below 32 are usually reserved
as control
codes by both your computer
and your printer.
While these
characters can be replaced by user-defined
characters,
it should
be avoided because of the effect on the normal control codes.
In our example, we'll assign the car a value of 60, which is the
code for the character "(" in the ASCII characters.
A rather ar-
bitrary selection, but this printer doesn't care!
Our chart would hardly be complete with just a picture of a
car, so in Figure 8-8 we've made completed grids for some other
symbols: a telephone (quite a strange mix of characters!). The in-
formation on the grids is now completed.
n Download character
definition command
You've
read
through
a long
explanation
of download
characters
and we haven't even told you the command
syntax
yet! Now the wait is over. This is the most complex command in
your printer
repertoire
and now you've
got the necessary
knowledge
to implement
it. Here it is:
(ESC) "&" CHR$(O) nl n2 m0 ml m2 dl d2 d3 . . . dx
Like the other printer's commands,
it starts with an (ESC)
(CHR$(27)). The next character is an ampersand
(&) (CHR$(38))
followed by a CHR$(O).
nl and n2 are used to specify
the ASCII values
of the
characters you are defining. The reason that there are two bytes
reserved for this is that your printer allows you to define many
characters with just a single command. nl is used to specify the
beginning of a range of characters to be defined; a.2 specifies the
end of the range. For instance, if you wanted to change the ap-
pearance of the numerals from 0 to 9 (which have ASCII codes
48 through
57), the command
would begin with (ESC)
"&"
CHR$(O) CHR$(48) CHR$(57) . . . Of course, you can also define
individual characters
by making nl and n2 equal.
The three bytes following the specification
of the range of
characters (m0, ml and m2) are used to specify the width of the
character and the space to be allowed on either side of it. The
left space (in dot column) is specified by m0 and the right space
is specified by m2. The second byte (ml) specifies the number
of columns of dots that will be printed by the character. By vary-
ing the width of the character
itself and the spaces around it,
you can actually create proportional
width characters.
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