CC2431 Datasheet, PDF (9/15 Pages) Texas Instruments – System-on-Chip for 2.4 GHz ZigBee-TM / IEEE 802.15.4 with Location Engine

CC2431
Path Loss vs. log-distance for source 0x85, Z=2.1082. A=42.4103, n=2.9773
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90
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10*log10(distance)
Figure 2: Path loss vs. log distance
2.1.2.1.4 RSSI Values
The RSSI values are the RSSI
measurements corresponding to the set of
reference coordinates. The RSSI values
are within the interval [-40 dBm, -95 dBm]
with precision 0.5 dBm. The negative sign
is removed in the value written. As an
example, in the case where the value
RSSI = -50.35 dB, this would be written
into the location engine as 50.5.
Note that a value of 0.0 must be written as
RSSI value for unused reference
coordinates. The engine will not function
correctly if only some of the parameters
are loaded.
2.1.2.2 Loading Parameters
All measured parameters are loaded into
the RF register MEASPARM. Before writing
to MEASPARM, a 1 must be written to the
register bit LOCENG.PARLD to indicate
that a set of measured parameters are
being written. Once the parameter load
process commences (LOCENG.PARLD
=1), all ten parameters must be written.
The measured parameters must be written
in the order [A, n, rssi0, rssi1, … rssi7] to
the MEASPARM register. Once the
parameter load process commences
(LOCENG.PARLD =1) it must be
completed. Eight RSSI values must be
written, so any unused slots must be
written as zeros. After all ten parameters
have been written, a 0 must be written to
the register bit LOCENG.PARLD.
2.1.3 Location Estimation
The estimated location coordinates are
given in meters in the interval [0.0, 63.5]
with precision 0.5 m. The data format uses
the LSB bit as the fractional part.
When reference coordinates and
measured parameters have been loaded,
the location estimate is calculated by
writing 1 to the LOCENG.RUN register bit.
The estimated coordinates can be read
from the LOCX and LOCY registers when
LOCENG.DONE is set to 1. This occurs
1200 system clock cycles (16/32 MHz)
after LOCENG.RUN was set to 1. The
Location Engine does not produce any
interrupt requests.
The estimated coordinates remain valid in
the LOCX and LOCY registers until new
SWRS034
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