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Run the program to see the printout below:
As you can see, both sets of characters (the original ROM characters
that the printer normally uses and the user-defined character set)
remain in the printer available for your use. The command to switch
between the two sets is used in lines 180 and 200 and has the following
format:
ESC%n
If n is 0, the normal ROM character set is selected. (This is the
default.) If n is 1, the user-defined character set is selected. If you select
the user-defined character set before you have defined any characters,
the command is ignored; the ROM characters are still used.
You can switch between character sets at any time, even in the
middle of a line. To try it, place semicolons at the end of lines 170 and
190 in the program above.
Copying ROM to RAM
After running the program above, if you select the user-defined
character set and try to print other characters, the only one that will print
is the heart. If you send the code for a character that is not defined,
nothing is printed, not even a space; it is as if it was not sent at all.
In many cases, you will want to redefine only a few of the characters,
leaving the rest of the alphabet as it is. As you have seen, it is possible
to switch back and forth between the normal character set and the user-
defined character set. Normally it is more convenient to copy all of the
standard characters from ROM to the area of RAM that holds the user-
defined character set. The format of the command to do this is as
follows:
Esc:000
If you use this command at the beginning of a program, then define
the special characters you want to change, you can then select the user-
defined character set and use it as your normal character set. There is
then no need to switch back and forth between sets.
6-16
Graphics and User-defined Characters