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An Introduction to Dot Matrix Printing
Chapter 4
An Introduction to Dot Matrix Printing
(Subtitled,
“Does a Dull Title Make a Topic Dull?“)
My Computer Can’t Do High Resolution Graphics!
Correction, your computer can do high resolution graphics - on the MX-70
printer. Any computer that has the BASIC CHR$ function and the correct
computer/printer interface can punch out super graphics on the MX-70. It’s as
easy as sending CHR$ (0), . . . through CHR$ (255).
Unfortunately, that may not be as simple as it sounds. If you are fluent in
Binary math, you know it takes 8 bits to count from 0 to 255 to specify the
above 256 codes. (2 to the 8th power is 256.) (If you aren’t fluent in Binary
math, it still does. Hang in there.)
Many computers and printer interfaces only support 7 bits of code data, hence,
transmit to the printer only the ASCII code numbers between O-127. At this
writing, Epson’s Apple parallel interface card is in this category since Apple
BASIC does not control the eighth bit. It is quite possible to drive the MX-70
nicely with only code numbers from 0 to 127, but certain things are more
difficult.
How Dot Martrix Printing Works
To really understand dot matrix printing, we have to understand how the print
head works. It contains 9 “wires” or “pins” positioned one above the other, as
seen in Figure 4-l.
Dot matrix
Figure 4-1
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