Freescale Semiconductor FRDM-FXS-MULTI-B Ficha De Dados
FXOS8700CQ
Sensors
Freescale Semiconductor, Inc.
Freescale Semiconductor, Inc.
23
7
Embedded Functionality
FXOS8700CQ is a low-power, digital output, 6-axis sensor with both I
2
C and SPI interfaces.
Extensive embedded functionality
is provided to detect inertial and magnetic events at low power, with the ability to notify the host processor of an event using either
of the two programmable interrupt pins. The embedded functionality includes:
of the two programmable interrupt pins. The embedded functionality includes:
•
8-bit or 14-bit accelerometer data which includes high-pass filtered data, and 8-bit or 16-bit magnetometer data
•
Four different oversampling options for the accelerometer output data, and eight for the magnetometer. The oversampling
settings allow the end user to optimize the resolution versus power trade-off in a given application.
settings allow the end user to optimize the resolution versus power trade-off in a given application.
•
A low-noise accelerometer mode that functions independently of the oversampling modes for even higher resolution
•
Low-power, auto-wake/sleep function for conserving power in portable battery powered applications
•
Accelerometer pulse-detection circuit which can be used to detect directional single and double taps
•
Accelerometer directional motion- and freefall-event detection with programmable threshold and debounce time
•
Acceleration transient detection with programmable threshold and debounce time. Transient detection can employ either
a high-pass filter or use the difference between reference and current sample values.
a high-pass filter or use the difference between reference and current sample values.
•
Orientation detection with programmable hysteresis for smooth transitions between portrait/landscape orientations
•
Accelerometer vector-magnitude change event detection with programmable reference, threshold, and debounce time
values
values
•
Magnetic threshold event detection with programmable reference, threshold, and debounce time
•
Magnetometer vector-magnitude change event detection with programmable reference, threshold and debounce time
values
values
•
Magnetic min/max detection circuit which can also be used for autonomous calibration of magnetic hard-iron offset
Many different configurations of the above functions are possible to suit the needs of the end application. Separate application
notes are available to further explain the different configuration settings and potential use cases.
notes are available to further explain the different configuration settings and potential use cases.
7.1
Factory calibration
FXOS8700CQ's integrated accelerometer and magnetometer sensors are factory calibrated for sensitivity and offset on each
axis. The trim values are stored in Non-Volatile Memory (NVM). On power-up, the trim parameters are read from NVM and
applied to the internal compensation circuitry. After mounting the device to the PCB, the user may further adjust the
accelerometer and magnetometer offsets through the OFF_X/Y/Z and M_OFF_X/Y/Z registers, respectively. For more
information on device calibration, refer to Freescale application note, AN4399.
axis. The trim values are stored in Non-Volatile Memory (NVM). On power-up, the trim parameters are read from NVM and
applied to the internal compensation circuitry. After mounting the device to the PCB, the user may further adjust the
accelerometer and magnetometer offsets through the OFF_X/Y/Z and M_OFF_X/Y/Z registers, respectively. For more
information on device calibration, refer to Freescale application note, AN4399.
7.2
8-bit or 14-bit accelerometer data
The measured acceleration data is stored in the OUT_X_MSB, OUT_X_LSB, OUT_Y_MSB, OUT_Y_LSB, OUT_Z_MSB, and
OUT_Z_LSB registers as 2’s complement 14-bit numbers. The most significant 8-bits of each axis are stored in the OUT_X, Y,
Z_MSB registers, so applications needing only 8-bit results simply read these three registers and ignore the OUT_X,Y, Z_LSB
registers. To do this, the f_read mode bit in CTRL_REG1 must be set.
OUT_Z_LSB registers as 2’s complement 14-bit numbers. The most significant 8-bits of each axis are stored in the OUT_X, Y,
Z_MSB registers, so applications needing only 8-bit results simply read these three registers and ignore the OUT_X,Y, Z_LSB
registers. To do this, the f_read mode bit in CTRL_REG1 must be set.
When the full-scale range is set to 2 g, the measurement range is -2 g to +1.999 g, and each count corresponds to 0.244 mg at
±14-bits resolution. When the full-scale is set to 8 g, the measurement range is -8 g to +7.996 g, and each count corresponds to
0.976 mg. The resolution is reduced by a factor of 64 if only the 8-bit results are used (CTRL_REG1[f_read] = 1). For further
information on the different data formats and modes, please refer to Freescale application note AN4076.
±14-bits resolution. When the full-scale is set to 8 g, the measurement range is -8 g to +7.996 g, and each count corresponds to
0.976 mg. The resolution is reduced by a factor of 64 if only the 8-bit results are used (CTRL_REG1[f_read] = 1). For further
information on the different data formats and modes, please refer to Freescale application note AN4076.
7.3
Accelerometer low-power modes versus high-resolution modes
FXOS8700CQ can be optimized for lower power or higher resolution of the accelerometer output data. High resolution is
achieved by setting the lnoise bit in register 0x2A. This improves the resolution (by lowering the noise), but be aware that the
dynamic range becomes fixed at ±4 g when this bit is set. This will affect all internal embedded functions (scaling of thresholds,
etc.) and reduce noise. Another method for improving the resolution of the data is through oversampling. One of the oversampling
schemes of the output data can be activated when CTRL_REG2[mods] = 0b10 which will improve the resolution of the output
data without affecting the internal embedded functions or fixing the dynamic range.
achieved by setting the lnoise bit in register 0x2A. This improves the resolution (by lowering the noise), but be aware that the
dynamic range becomes fixed at ±4 g when this bit is set. This will affect all internal embedded functions (scaling of thresholds,
etc.) and reduce noise. Another method for improving the resolution of the data is through oversampling. One of the oversampling
schemes of the output data can be activated when CTRL_REG2[mods] = 0b10 which will improve the resolution of the output
data without affecting the internal embedded functions or fixing the dynamic range.
There is a trade-off between low power and high resolution. Low power can be achieved when the oversampling rate is reduced.
When CTRL_REG2[mods] = 0b10, the lowest power is achieved, at the expense of higher noise. In general, the lower the
selected ODR and OSR, the lower the power consumption. For more information on how to configure the device in low-power or
high-resolution modes and understand the benefits and trade-offs, please refer to Freescale application note AN4075.
When CTRL_REG2[mods] = 0b10, the lowest power is achieved, at the expense of higher noise. In general, the lower the
selected ODR and OSR, the lower the power consumption. For more information on how to configure the device in low-power or
high-resolution modes and understand the benefits and trade-offs, please refer to Freescale application note AN4075.