Epson Apex-80 - Manual (Page 64)

The graphics command format
There are several different graphics commands giving different
horizontal dot
densities
and printing speeds. Because the format is
almost the same for all the commands, however, the example here
keeps things simple by using only the single-density graphics command,
ESC K. In single-density graphics, there are 60 dots per inch
horizontally.
The command to enter single-density graphics mode is ESC K nl n2.
In BASIC the command is given in this format:
LPRINT CHR$(27);"K";CHR$(n1);CHR$(n2);
ESC K specifies single-density graphics, and the next two numbers
(nl and n2) specify the number of columns reserved for graphics.
Column reservation numbers
Even in single-density graphics mode, one 8-inch line can
accommodate 480 columns of graphics; in quadrupledensity, almost
2000 columns can fit on the same 8-inch line. Since the printer does
not use decimal numbers larger than 255, the graphics commands use
two numbers for reserving columns.
Because the commands are set up for two numbers, you must supply
two even if you need only one. When you need fewer than 256
columns, it is easy to determine n1 and n2: n1 is the number of
columns you are reserving and n2 is zero. For example, to send data for
200 columns of graphics, n1 is 200 and n2 is 0.
For more than 256 columns of graphics data, n2 is the number of
complete groups of 256 columns, and n1 is the number of columns to
complete the line. For example, to send 1632 columns of graphic data,
nl is 96 and n2 is 6 because 96 + (6
x
256) = 1632.
You can calculate both nl and n2 by dividing the total number of
columns by 256. The quotient is n2 and the remainder is nl. If you are
using a programming language with MOD (modulus) and INT (integer)
functions, you can use the following formulas, in which n is the total
number of columns.
nl = n MOD 256
n2 = INT (n/256)
Introduction to Dot Graphics 6.5