Firing The Pins; Usable Pins Labelled Sequentially - Epson FX-80 User Manual
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Decimal
~
_____ 7·bit computers
I
"
0
I'
"n't
""oh
top pin
o o
o
o
§
o
Usable
pins
Boltom pin
__ used only tor
g.pin Graphics Mode
Figure 11·2. Usable pins labelled sequentially.
In deference to users who have this problem, sample graphics pro-
grams in this manual will be limited to 7 pins whenever possible. Even
so, there may be times when 7-bit computer users have to make ad-
justments. See Appendix H for ways of handling this dilemma.
Firing the pins
So much for problems. Once the printer is in Graphics Mode, the
next step is to tell the print head which pins to fire at each new posi-
tion. This is done by sending numbers via the CHR$ function. Each
number sent represents a unique combination of pins.
The eight pins are not numbered 1 through 8 as one might expect.
Since computers use the the binary number system (Is and Os), each
pin corresponds to one bit in a binary number. In the decimal system,
this means that each pin of the print head must be expressed as a
power of two. That's right: 1, 2, 4, 8, 16, 32, 64, and 128.
Why powers of two? Wouldn't
it
be easier to label the pins
1
to 8?
Well, that works fine if you only want to fire one pin at a time, but a 1
132
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