Accelerometer; Table 3-10. Spi Interface; Figure 3-35. Accelerometer Block Diagram - Motorola APX 3000 Detailed Service Manual

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3.4

Accelerometer

3.4.1 General Overview
Accelerometer capabilities are achieved by the 3-axes nano" accelerometer IC (LIS331DL) located
on the expansion board. The LIS331DL is a digital output linear accelerometer in a LGA package. It
is powered by the 3.3 LDO regulator placed in the expansion board. The complete device includes a
sensing element and an IC interface to provide the signal to the AVR IC. When acceleration is
applied to the sensor, an imbalance in capacitance is produced. This imbalance is measured and
converted to an analog voltage that is finally available to the user by an analog to digital converter.
The acceleration data is accessed through an SPI interface and presented to the AVR.
NOTE: Please refer to User Guide and CPS for further details.
The registers embedded on the LIS331DL are accessed through SPI serial interface. The following
pins are responsible for the SPI communication.
CS is the serial port enable and it is controlled by the AVR (SPI Master). It goes low at the start of the
transmission and toggles high at the end. SPC is the serial port clock and it is also controlled by the
AVR. It is stopped high when the CS is high (no transmission). SDI and SDO are respectively the
serial data input and output. These lines are driven at the falling edge of SPC and should be capture
at the rising edge of SPC.
3.3V LDO
Core
and
I/O
Voltage
Accelerometer
LIS331DLH
(Bus Slave)

Figure 3-35. Accelerometer Block Diagram

Table 3-10. SPI Interface

Pin Name
CS
SPC
SDI
SDO
SPI
Accelerometer
Data Bus
AT32UC3A
(Bus Master)
Interrupts
Pin Description
SPI Enable
SPI Serial Port Clock
SPI Serial Data Input
SPI Serial Data Output
Theory of Operation
AVR
: Accelerometer