Epson LQ-860 - Impact Printer, User Manual

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Twenty-four-pin graphics
The graphics mode that takes full advantage of this printer’s print
head is 24-pin graphics. This mode has five densities, but for
simplicity this explanation deals with only one of them, triple-
density.
Triple-density prints up to 180 dots per inch horizontally. As the
print head moves across the paper, every 1/180th of an inch it must
receive instructions about which of its 24 pins to fire. At each
position it can fire any number of pins, from none to 24. This means
that the printer must receive 24 bits of information for each column
it prints. Because the printer uses 8-bit bytes of information in
communicating with the computer, it needs three bytes of
information for each position.
Pin labels
To tell the printer which pins to fire in each column, you first divide
each of the vertical columns into three sections of eight pins each
and consider each section separately. Because there are 256 possible
combinations of the eight pins in each section, you need a
numbering system that allows you to use a single number to specify
which of the 256 possible patterns you want. This numbering
system is shown below:
128
64
32
16
8
4
2
1
To fire any one pin, you send its number to the printer. To fire more
than one pin at the same time, add up the numbers of the pins and
send the total. Using these labels for the pins, you fire the top pin by
sending 128. To fire the bottom pin, you send 1. If you want to fire
only the top and bottom pins, you simply add 128 and 1 and send 129.
4-10 Software and Graphics