User Manual

ZSTAR3 Sensor Board Description
ZSTAR3 Reference Design Manual, Rev. 0.1
3-18 Freescale Semiconductor
Preliminary
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application note AN3447 - Implementing Auto-Zero Calibration Techniquefor accelerometers on
www.freescale.com.
3.2.3 Analogue sensor software support
The 3-axis accelerometer Sensor MMA7360L provides three separate analog levels for the X, Y and Z
axis. These outputs are ratiometric which means that the output offset voltage and sensitivity will scale
linearly with applied supply voltage. This is a key feature when interfacing to a microcontroller with A/D
converter reference levels tied to a power supply, because it provides system level cancellation of supply
induced errors in the analog to digital conversion process.
During the analog-to-digital conversion in the microcontroller, 10-bit resolution is used. MC13213 A/D
channels 0, 1 and 2 are connected to X (channel 1), Y (channel 2) and Z (channel 0) outputs of the
MMA7360L. The microcontroller’s APCTL1 register enables these ADC channels for pin I/O control by
the ADC module.
The ADCCFG register controls the selected mode of operation, clock source, clock divide, and
configuration for low power or long sample time.
The MMA7360L sensor has implemeted digital output of freefall detection module. This output is
connected direct to KBI(Keyboard interrupt module) and it’s used as default source of freefall detection.
3.2.4 Digital sensor software support
The MMA7450L provides a lots of various features, that almost are using by the ZSTAR3 demo. Complete
communication with sensor is done by digital interface. MMA7450L supports two standards of digital
comunication: SPI(Serial Peripherial Interface) and IIC(Inter-Integrated Circuit).
3.2.5 Power Management
A CR2032 Lithium battery provides a fairly limited charge for such a realtime-like demo that demands
frequent transmissions. Some sort of power management has to be implemented in order to keep the
current consumption at a reasonable level.
Typically, current consumptions of Sensor Board components are as follows:
• SIP - System in Pack MC13213
— 2.4GHz transceiver of MC13213
– in Off mode, 200nA
– in Hibernate mode, 2.3µA
– in Doze mode, 35µA
– in Idle mode, 500µA
– in Transmit mode, 30mA
– in Receive mode, 37mA
— 8-bit microcontroller of MC13213