Attribute Byte; Proportional Print - Epson FX Series User Manual

Attribute byte

The attribute byte is the first of the 12 data numbers required to
define any character. At print time it controls two aspects of the way
the character is printed. First, it determines which 8 pins of the print
head are used to print the character. For most characters, the top 8
pins are used, but for lowercase characters with descenders (like g and
p), the bottom 8 pins can be used.
So how does the attribute byte determine which 8 pins are used? At
print time, the printer checks the attribute byte before each character
is printed. If the high-order bit is on, the top 8 pins of the print head
are used; if the high-order bit is off, the bottom 8 are used. To put it
another way, if the attribute byte for a given character is 128 or
greater, the top 8 pins are used; if it is 127 or less, the bottom 8 are
used. Figure 15-4 demonstrates these choices.
Figure 15-4. Pins chosen by attribute byte

Proportional print

The attribute byte also contains information used to print a charac-
ter in Proportional Mode. It tells the printer in which columns to start
and stop printing for each character. If you label the 11 columns deter-
A T T R I B U T E B Y T E
If attribute byte is less than 128,
bottom eight pins are used
A T T R I B U T E B Y T E
ON
If attribute byte is 128 or greater,
top eight pins are used
203