of Microprocessors

MICROPROCESSORS 147
The best device for printed graphics output is a plotter. These produce
dtawings as well as text by inking smooth lines between designated
endpoints using an X-Y coordinate system. Drawing pens are easily
interchangeable for different colors or even different line widths. Quality is
usually high, since only the endpoints need be on the fixed grid and no dot
structure is evident in the lines. Some models show irregularities and wiggles
in plotted lines at certain angles, however, due to the stepper motor drive
system employed. Also the X-Y grid itself is fairly fine with 200 and 254
(metric) grids pet inch being common densities. Unlike a dot matrix printer
in which the print time depends only on the image size, plotting time
depends on the image complexity. For most images, plotters come out being
substantially slower than dot matrix printers. Only recently have plotters
become inexpensive enough to be practical to connect to a microcomputer. It
is now possible to get a unit capable of8.5 X ll-inch plots for under $500,
while a unit with extra features such as automatic circle drawing and an 11 X
17-inch plotting size can be under $1,000. Larger sizes are available but at
sharply higher prices.
Miscellaneous Devices
Many other miscellaneous peripheral devices are found on microcomputers
but not as frequently as those mentioned above. One of these is a
telephone modem. The word is actually a contraction of "modulator" and
"demodulator." In essence, it allows a computer to send binary digital
information over telephone lines by modulating an audio carrier tone with
data to be sent and also demodulating the received tone signal to recover
received data. This then allows a microcomputer to call up a mainframe and
exchange data with it or call another microcomputer and exchange program
or data files. Computer "bulletin boards" operated by clubs or hobbyists can
also be accessed by any computer equipped with a modem. Data transmission
speeds are moderately high with common values being 30 and 120 bytes per
second. Prices range from under $200 for a 30-byte/sec unit up to $400-500
for a 120-byte/sec unit. Transmission accuracy for modern units is remarkably
good, even over long-distance telephone circuits.
Another common convenience item is a computer-readable clock and
calendar. Besides allowing the operating system to automatically keep track
of creation and update dates for data files, such a clock can be useful in
keeping track of time for real-time music input or synthesis applications.
Actually, one would think that with three-dollar stick-on electronic clocks
everywhere, they would be built into all computers, regardless ofprice. Such
is not the case, however, and in fact such a capability is usually either a
moderately expensive add-on board Ot a highly promoted standard feature.
Speech input and output capability is also occasionally seen. Of these,
speech output has been much more successful, although speech input is