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H The seven bit dilemma
Some computers (not the IBM-PC fortunately!) don’t have the
capability to send eight bits on their parallel interface, but can
only send seven bits. This would make it impossible for these
computers to use this printer’s block graphics characters and
special symbols if our engineers hadn’t thought of a solution.
(All of these characters have ASCII codes greater than 127
which means that the eighth bit must be on to use them.) The
solution lies in the three control codes given in the following
table:
Table 5-3
Eighth bit controls
~1 Accept the eighth bit “as is” from cESCj ,,#,,
n Block graphics characters and special symbols
Besides the upper and lower case letters and symbols that we
are by now familiar with, your printer has a whole different set
of characters that are for special uses. These characters include
block graphics for drawing forms and graphs, and special sym-
bols for mathematical, engineering and professional uses. The
special characters are included in two character sets.. The
character set you normally use with IBM mode is called
character set #l. The special characters are printed out when
you send ASCII codes 160-255 to the printer.
Your printer also offers character set #2 which is almost the
same as character set #l except for the addition of ASCII codes
3--6,20,21,26, and 128-159. Character set #2 is selected with
(ESC)“G”; to go back to character set #l, use (ESC“7”.
You can also specify the power-on default character set by set-
ting DIP switch l-4 on for character set #l and off for character
set #2. The following program will print out all of the graphics
characters available: