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Twenty-four-pin graphics
The graphics mode that takes full advantage of the printer’s print head is
24-pin graphics. This mode has five densities, but for simplicity this
explanation begins with triple-density.
Triple-density prints up to 180 dots per inch horizontally. As the print
head moves across the paper, it must receive instructions every l/180th
of an inch 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. Since the printer
uses B-bit bytes of information in its communication 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. Since 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
iii
16
:
2
1
To fire any one pin, you send its number. To fire more than one pin at
the same time, you add up the numbers of the pins and send the sum to
the printer. 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.
By adding the appropriate label numbers together, you can fire any
combination of pins. The following three examples show you how to
calculate the number that will fire a particular pattern of pins.
Using Software and Graphics
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