ADXL180
Rev. 0 | Page 9 of 56
TERMINOLOGY
Full-Scale Range (FSR)
The full-scale range of a device, also referred to as the dynamic
range, is the maximum and minimum
g
level that reports on the
output following the internal filtering. As a reference, there is
usually a trade-off in increased sensitivity and resolution for
decreased full-scale range, and vice versa.
Noise
Device noise is the noise content between 10 Hz and 400 Hz, as
noted in the Specifications Table 1. Device noise can be measured
by performing an FFT on the digital output and measuring the
noise content between the specified frequency limits.
Sensitivity
The sensitivity of a device is the amount of output change per
input change. In this device, it is most usually referred to in
units of LSB/
g
.
Scale Factor
The scale factor is the amount of input change per output change.
In this device, it is most usually referred to in units of
g
/LSB.
Offset
Offset is the low frequency component of the output signal that
is not due to changes in input acceleration. Slow moving effects,
such as temperature changes and self-heating during start up,
may affect offset, but the time scale for these effects is beyond
that of a typical shock or crash event.
Auto-Zero
Auto-zero is an offset compensation technique intended to
reduce the long term offset drift effects of temperature and
aging. This technique is designed to limit interaction with true
acceleration signals. For more information, see Figure 30.
Rise/Fall Times
The device rise time is defined as the amount of time necessary
for the Manchester encoded signal (I
MOD
) to transition from 10%
to 90% of its final value (I
SIG
). Device fall time is the amount of
time required for the I
MOD
signal to fall from 90% of I
SIG
to within
10% of I
IDLE
.
Idle Current
Idle current is the current of the device when at rest, waiting for
a synchronization pulse, or in between current modulation.
Modulation Current
Modulation current is the amount of current that the ADXL180
device pulls from the bus when communicating. For more
information, see Figure 7.
Phase
A phase is a stage in the ADXL180 state machine. For more
information, see Figure 20.
Mode
Mode refers to the selection of the Phase 2 method of device
data communication. The ADXL180 is configurable into four
unique operating modes.
CRC
A cyclic redundancy check (CRC) is calculated from a set of
data and then transmitted alongside that data. If the calculation
technique is defined and known to the receiving device, the
receiver can then check whether the CRC bits match the data. If
they do not match, a transmission error has occurred.
Parity
Parity is defined by the count of 1s in a binary string of data.
If this count is even, then the data is determined to have even
parity. Often a bit is used, such as the CUPAR, in a configuration
register that is defined in such a way as to establish a particular
parity in the register to detect single bit changes during the life
of the device. This is possible because a single bit change changes
parity and a monitor circuit can detect this. Similarly, a parity
bit can be added in a data transmission to detect single bit errors
if the parity of communication is preestablished for the transmit
and receive systems.
