
Send it a Message
Not all codes actually print on either the screen or the printer. Most special or “control” codes don’t really PRINT anything, even though we must precede them with a PRINT to “push them down the line” to the printer.
For example, type the following at the command level:
PRINT CHR$(14); "DOUBLE WIDE"
and see the words appear in double width (not double spaced).
D O U B L E W I D E
Figure
LIST the program to paper again. Notice that the double width feature is no longer switched on. The message: EACH TIME WE WISH TO PRINT SOMETHING IN THE DOUBLE WIDE MODE, WE MUST PRECEDE IT WITH CONTROL CODE 14.
When that LINE is finished printing, the double width feature is automatically
turned off.
Now that we understand line 20, let’s add it in and RUN our
G R E E T I N G S F R O M T H E G R A P H I C
M X - 7 0
Figure
Pretty nice - eh? If you wish, do another LIST. Look at the printout to feel confident that DOUBLE WIDTH really got switched off.
The programming in line 30 is a bit more exotic. It consists of only 1
PRINT statement to “push” 1 TAB, a control character, a “K,” and two
ASCII characters to the printer. The control code 27 stands for “ES-
CAPE,” which forces us to GOSUB to another topic.
The Great EscapeThe
19