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To fire any one pin, you send its number. To fire more than one pin at
the same time, add up the numbers of the pins and send the sum to the
printer. With 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 the top and
bottom pins together, add 128 and 1, then send 129.
By adding the appropriate label numbers together, you can fire any
combination of pins. Figure 62 shows three examples of how to
calculate the number that will fire a particular pattern of pins.
With this numbering system, any combination of the eight pins adds
up
to a decimal number between 0 and 255, and no numbers are
duplicated.
Since there are 24 pins in each column, you must make a calculation
for each of the three sections in each column. As you can see, this
method of planning and printing dot graphics requires considerable
calculation. Because tripledensity uses 180 columns per inch, printing a
single line of triple-density graphics only one inch long requires 540
numbers. Fortunately commercial programs can do the calculations for
you.
Before you can put these numbers in a graphics program, however,
you need to know the format of the graphics command.
Graphics Commands
The graphics m&e commands are quite different from the other
commands covered so far in this manual. For most of the other modes,
Figure 6-1.
pin numbering system
I
Figure 62.
Calculations /or pin pattems
6-4
Graphics and
User-defined Characters