Book Analog Interfacing to Embedded Microprocessors
ity, or any other real-world parameter. Whatever is being measured is con-
verted to a standard unit before it is transmitted to the controlling processor
via the IEEE 1451 interface. The IEEE 1451 standard permits sensors to
support the following units:
length (in meters)
mass (in kilograms)
time (in seconds)
current (in amps)
temperature (degrees kelvin)
amount of substance (mole)
luminous intensity (candela)
plane angle (radians)
solid angle (meters2)
Whatever unit the sensor measures in, it must be converted to these standard
units. A sensor may be measuring speed in miles per hour or furlongs per
fortnight, but it must be converted by the STIM microprocessor to meters per
second before transmission over the IEEE 1451 interface.
When the controlling processor reads sensor data from an IEEE 1451
sensor, what gets transmitted is a string of exponents, one for each of these
values
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