113
DEFINING YOUR OWN NLQ CHARACTERS
As you have probably noticed, NLQ characters are printed
by two passes of the print head. Half of the character is printed
on the first pass, and the remainder on the second pass. The
paper is rolled up half a dot height in between passes to let
the print head print dots on the second pass that overlap the
previous dots, in order to fill in the spaces and produce denser
characters. Additionally, the print head speed is halved, and
the dots are printed at double the density of draft characters.
For this reason, NLQ characters can contain up to 23 dots
in the horizontal direction.
Fundamentally, the process to define and print downloaded
NLQ characters is the same as for draft characters, except that
you must supply about four times as mnch character data,
and you must design the character with the two passes of the
print head in mind. There are small differences in the way the
attribute information is processed also.
In the draft quality mode the attribute byte carries the
descender data, and specifies the start and end printing col-
umns. In the NLQ mode, the first bit also carries the descender
data as with the draft characters, but the next three bits describe
the character’s left space, and the last four bits describe the
right space. Appropriate allocation of data in these seven bits
lets you place the character where you like within the grid,
with the restriction that the character must be at least 9 dots
wide.
Use the grid in Figure 7-6 to help plot the data. Due to the
two-pass process, NLQ characters can contain up to 16 dots
vertically. ml to m23 are the data for the first pass, and m24
to m46 are the data for the second pass.
To make the character data easier to calculate, put the first
pass dots inside the boxes on the grid when you are designing
your characters, and the second pass dots on the lines. Re-
member that adjacent dots may not overlap on the same pass;
in other words, if one dot is in a box, its adjacent dot on the
same pass may not be on a line. Therefore, to make smooth
characters, put the dots needed to overlap any spaces in a
character in the appropriate places in the second pass grid.