cd00098549

AN2335
Application note
LIS302DL: 3-Axis - ±2g/±8g digital output
ultracompact linear accelerometer
Introduction
This document is intended to give application notes for the low-voltage 3-axis digital output
linear MEMS accelerometer provided in LGA package.
The LIS302DL is an ultra compact low-power three axes linear accelerometer that includes
a sensing element and an IC interface able to take the information from the sensing element
and to provide the measured acceleration to the external world through I2C/SPI serial
interface.
The sensing element, capable of detecting the acceleration, is manufactured using a
dedicated process developed by ST to produce inertial sensors and actuators in silicon.
The IC interface instead is manufactured using a CMOS process that allows high level of
integration to design a dedicated circuit which is factory trimmed to better match the sensing
element characteristics.
The LIS302DL has a user selectable full scale of ±2g, ±8g and it is capable of measuring
accelerations with an output data rate of 100Hz or 400Hz. A self-test capability allows the
user to check the correct operation of the system.
The device features two independent highly programmable interrupt sources that can be
configured either to generate an inertial wake-up interrupt signal when a programmable
acceleration threshold is exceeded along one of the three axes or to detect a free-fall event.
Two independent pins can be configured to provide interrupt signals to connected devices.
The LIS302DL is available in plastic SMD package and it is specified over a temperature
range extending from -40°C to +85°C.
The ultra small size and weight of this package make it an ideal choice for handheld portable
applications such as cell phones and PDAs or any other application where reduced package
size and weight are required.
October 2006
Rev 2
1/40
www.st.com
Contents
AN2335
Contents
1
Theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2
Electrical connection and board layout hints . . . . . . . . . . . . . . . . . . . . . 7
2.1
Electrical connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2
Soldering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4
Digital interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1
4.2
5
7
2/40
4.1.1
I2C Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1.2
I2C Subsequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
SPI bus interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.1
Read & write protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2.2
SPI read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.3
SPI Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2.4
SPI Read in 3-wires mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Registers description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1
6
I2C Bus interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Registers address map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1.1
Reserved Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1.2
Registers loaded at Boot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
About control registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.1
CTRL_REG1 (20h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.2
CTRL_REG2 (21h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.3
CTRL_REG3 (22h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Data and status registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1
WHO_AM_I (0Fh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.2
STATUS_REG (27h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.3
OUTX (29h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.4
OUTY (2Bh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
AN2335
Contents
7.5
8
9
Free-Fall and Wake-Up Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.1
HP_FILTER_RESET (23h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.2
FF_WU_CFG_1 (30h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.3
FF_WU_SRC_1 (31h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
8.4
FF_WU_THS_1 (32h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.5
FF_WU_DURATION_1 (33h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.6
FF_WU_CFG_2 (34h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.7
FF_WU_SRC_2 (35h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.8
FF_WU_THS_2 (36h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
8.9
FF_WU_DURATION_2 (37h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Application Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.1
START-UP SEQUENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.2
READING ACCELERATION DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.2.1
Using the Status Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.2.2
Using the Data-Ready Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
9.3
Understanding acceleration data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9.4
Interrupt generation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
9.5
INERTIAL WAKE-UP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.6
10
OUTZ (2Dh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.5.1
HP Filter Bypassed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
9.5.2
Using the HP Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Free-Fall Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.6.1
Roll function not used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.6.2
Roll function applied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
9.7
Output data rate selection and reading timing . . . . . . . . . . . . . . . . . . . . . 37
9.8
Data ready vs. interrupt signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3/40
List of tables
AN2335
List of tables
Table 1.
Table 2.
Table 3.
Table 4.
Table 5.
Table 6.
Table 7.
Table 8.
4/40
Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Serial interface pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Registers address map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Output Data Registers content vs. Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Output Data Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Timing Value to Avoid Loosing the Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
AN2335
List of figures
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Device block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
LIS302DL electrical connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
I2C Subsequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Read & write protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
SPI read protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Multiple bytes SPI read protocol (2 bytes example) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
SPI Write Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Multiple Bytes SPI Write Protocol (2 bytes example) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
SPI Read Protocol In 3-wires Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Digital Processing Chain Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
FF_WU_CFG_1,2 High and Low value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
DCRM bit function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Interrupt Generation Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Free-Fall, Wake-Up Interrupt Generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Reading Timing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Interrupt and dataready signal generation block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . 38
Data Ready Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
5/40
Theory of operation
1
AN2335
Theory of operation
The LIS302DL is an ultracompact, low-power, digital output 3-axis linear accelerometer
packaged in a LGA package. The complete device includes a sensing element and an IC
interface able to take the information from the sensing element and to provide a signal to the
external world through an I2C/SPI serial interface (Figure 1).
A proprietary process is used to create a surface micro-machined accelerometer. The
technology allows to carry out suspended silicon structures which are attached to the
substrate in a few points called anchors and are free to move in the direction of the sensed
acceleration. To be compatible with the traditional packaging techniques a cap is placed on
top of the sensing element to avoid blocking the moving parts during the moulding phase of
the plastic encapsulation.
When an acceleration is applied to the sensor the proof mass displaces from its nominal
position, causing an imbalance in the capacitive half-bridge. This imbalance is measured
using charge integration in response to a voltage pulse applied to the sense capacitor.
At steady state the nominal value of the capacitors are few pico Farad and when an
acceleration is applied the maximum variation of the capacitive load is of few femto Farad.
The complete measurement chain is composed by a low-noise capacitive amplifier which
converts into an analog voltage the capacitive unbalancing of the MEMS sensor and by and
by analog-to-digital converters.
The acceleration data may be accessed through an I2C/SPI interface thus making the
device particularly suitable for direct interfacing with a microcontroller.
Data synchronization in digital system employing the device is made simpler through the
usage of the Data-Ready signal (RDY) which indicates when a new set of measured
acceleration data is available thus simplifying data synchronization in digital system
employing the device itself.
The LIS302DL features also two independent fully programmable interrupt sources which
can be programmed to generate an interrupt signal when a programmable acceleration
threshold is exceeded along one of the three axes or to detect a free-fall event.
The IC interface is factory calibrated for sensitivity (So) and Zero-g level (Off).
The trimming values are stored inside the device by a non volatile structure. Any time the
device is turned on, the trimming parameters are downloaded into the registers to be
employed during the normal operation. This allows the user to employ the device without
further calibration.
Figure 1.
Device block diagram
X+
Y+
a
CS
CHARGE
AMPLIFIER
Z+
MUX
A/D
CONVERTER
I2C
CONTROL LOGIC
SPI
Z-
SCL/SPC
SDA/SDO/SDI
SDO
YX-
SELF TEST
6/40
REFERENCE
TRIMMING
CIRCUITS
CLOCK
CONTROL LOGIC
INT 1
&
INTERRUPT GEN.
INT 2
AN2335
Electrical connection and board layout hints
2
Electrical connection and board layout hints
2.1
Electrical connection
The typical electrical connection of the LIS302DL is shown in Figure 2
Figure 2.
LIS302DL electrical connection
Vdd
Vdd_IO
1
6
Z
1
X
Y
10uF
13
6
Top VIEW
8
TOP VIEW
DIRECTION OF THE
DETECTABLE
ACCELERATIONS
SCL/SPC
SDO
INT2
13
INT1
CS
8
SDA/SDI/SDO
100nF
GND
Digital signal from/to signal controller.Signal’s levels are defined by proper selection of Vdd_IO
The LIS302DL is designed to operate with a voltage supply spanning from 2.16V up to 3.6V
while the serial interface can work down to 1.8V.
The device core is supplied through Vdd line (Vdd typ=2.5V) while the I/O pads are supplied
through Vdd_IO line. The typical current consumption in normal mode at 2.5V is 400μA.
Both the voltage supplies must be present at the same time to have proper behavior of the
IC. It is possible to remove Vdd mantaining Vdd_IO without blocking the communication bus.
Adequate power supply decoupling is required to ensure IC performances. The optimum
decoupling is achieved by using two capacitors of different types that target different kinds of
noise on the power supply leads. To attenuate high frequency transients, spikes, or digital
hash on the line it is recommended the use of one 100nF ceramic or polyester capacitor
which must be placed as close as possible to device Vdd lead. For filtering lower-frequency
noise signals, a larger aluminum capacitor of 10μF or greater should be placed near the
device in parallel to the former capacitor. It is recommended to place these capacitors as
near as possible to the pin 6 of the device.
The functionality of the device and the measured acceleration data are selectable and
accessible through the I2C/SPI interface. When using the I2C, CS must be tied high while
SDO allows to select among two device addresses in case two sensors must be connected
on the same bus. Whenever one single sensor is present on the same I2C bus it is
recommended either to connect SDO to Vdd_IO or to leave it floating.
7/40
Absolute maximum ratings
2.2
AN2335
Soldering information
The LGA-14 package is lead free and green package qualified for soldering heat resistance
according to JEDEC J-STD-020C. Land pattern and soldering recommendations are
available upon request.
3
Absolute maximum ratings
Stresses above those listed as “absolute maximum ratings” may cause permanent damage
to the device. This is a stress rating only and functional operation of the device under these
conditions is not implied. Exposure to maximum rating conditions for extended periods may
affect device reliability.
Table 1.
Absolute maximum ratings
Symbol
Vdd
Vdd_IO
Vin
Ratings
Supply voltage(1)
(1)
I/O pins Supply voltage
Input voltage on any control pin
(CS, SCL/SPC, SDA/SDI/SDO, CK)
Maximum Value
Unit
-0.3 to 6
V
-0.3 to 6
V
-0.3 to Vdd_IO +0.3
V
3000g for 0.5 ms
APOW
Acceleration (Any axis, Powered, Vdd=2.5V)
AUNP
Acceleration (Any axis, Unpowered)
TOP
Operating Temperature Range
-40 to +85
°C
TSTG
Storage Temperature Range
-40 to +125
°C
ESD
Electrostatic discharge protection
10000g for 0.1 ms
3000g for 0.5 ms
10000g for 0.1 ms
Class 1: 0 - 2KV HBM
1. Supply voltage on any pin should never exceed 6.0V
8/40
Warning:
This is a ESD sensitive device, improper handling can cause
permanent damages to the part.
Warning:
This is a mechanical shock sensitive device, improper
handling can cause permanent damages to the part.
AN2335
4
Digital interfaces
Digital interfaces
The registers embedded inside the LIS302DL may be accessed through I2C and SPI serial
interfaces. The latter may be SW configured to operate either in 3-wire or 4-wire interface
mode.
The serial interfaces are mapped onto the same pads. To select/exploit the I2C interface, CS
line must be tied high (i.e connected to Vdd_IO).
Table 2.
Serial interface pin description
Pin Name
SPI chip select (CS)
I2C/SPI selector (1: I2C mode; 0: SPI enabled)
CS
SCL/SPC
4.1
Pin Description
SPI CK line (SCL)
I2C clock line (SPC)
SDI/SDA/SDO
I2C serial data (SDA)
SPI data in (SDI)
SPI data out (SDO) -for 3-wire SPI mode-
SDO
I2C less significant bit of device address
SPI data out (SDO) -for 4-wire SPI mode-
I2C Bus interface
The LIS302DL I2C is a bus slave. The I2C is employed to write/read the data into/from the
registers.
The relevant I2C terminology is shown in Table 3:
Table 3.
Terminology
Term
Transmitter
Receiver
Description
The device which sends data to the bus
The device which receives data from the bus
Master
The device which initiates a transfer, generates clock signals and terminates
a transfer
Slave
The device addressed by the master
There are two signals associated with the I2C bus: the Serial Clock Line (SCL) and the
Serial DAta line (SDA). The latter is a bidirectional line used for sending and receiving the
data to/from the interface. Both the lines are connected to Vdd_IO through a pull-up resistor
embedded inside the LIS302DL. When the bus is free both the lines are high.
The I2C interface is compliant with Fast Mode (400 kHz) I2C standards as well as the
Normal Mode.
9/40
Digital interfaces
4.1.1
AN2335
I2C Operation
The transaction on the bus is started through a START (ST) condition which is defined as a
HIGH to LOW transition on the data line while the SCL line is held HIGH. After the START
condition has been generated by the Master, the bus is considered busy. The next byte of
data transmitted contains the address of the slave in the first 7 bits and the eighth bit tells
whether the Master is receiving data from the slave or transmitting data to the slave (SAD
subsequence). When an address is sent, each device in the system compares the first
seven bits after a start condition with its own address. If they match, the device considers
itself addressed by the Master.
The Slave ADdress (SAD) associated to the LIS302DL may be selected among the two
predefined values 0011100b or 0011101b depending on the logic level present on SDO pin.
In details, if SDO pin is either connected to Vdd_IO or left unconnected the slave address is
0011101b, otherwise when it is connected to GND the slave address is 0011100b.
Whenever it is not needed to place two sensors on the same bus it is recommended to use
the slave address 0011101b by either connecting the SDO pin to Vdd_IO or leaving it
floating.
Data transfer with acknowledge is mandatory. The transmitter must release the SDA line
during the acknowledge pulse. The receiver must then pull the data line LOW so that it
remains stable low during the HIGH period of the acknowledge clock pulse. A receiver which
has been addressed is obliged to generate an acknowledge after each byte of data has
been received.
The I2C embedded inside the LIS302DL behaves like a slave device and the following
protocol must be adhered to. After the start condition (ST) a salve address is sent, once a
slave acknowledge (SAK) has been returned, a 8-bit sub-address will be transmitted: the 7
LSb represent the actual register address while the MSB enables address auto increment. If
the MSb of the SUB field is 1, the SUB (register address) will be automatically incremented
to allow multiple data read/write. Otherwise if the MSB of the SUB field is ‘0’, the SUB will
remain unchanged and multiple read/write on the same address can be performed.
The slave address is completed with a Read/Write bit. If the bit was ‘1’ (Read), a repeated
START (SR) condition will have to be issued after the two sub-address bytes; if the bit is ‘0’
(Write) the Master will transmit to the slave with direction unchanged.
Transfer when Master is writing one byte to slave
Master
ST
SAD + W
SUB
Slave
DATA
SAK
SAK
SP
SAK
Transfer when Master is writing multiple bytes to slave:
Master
ST
SAD + W
Slave
SUB
SAK
DATA
SAK
DATA
SAK
SP
SAK
Transfer when Master is receiving (reading) one byte of data from slave:
Master
Slave
10/40
ST
SAD + W
SUB
SAK
SR
SAK
SAD + R
NMAK
SAK
DATA
SP
AN2335
Digital interfaces
Transfer when Master is receiving (reading) multiple bytes of data from slave
Master
ST
SAD + W
Slave
SAK
Master
Slave
SUB
SR
SAD + R
SAK
SAK
MAK
DATA
MAK
NMAK
DATA
SP
DATA
Data are transmitted in byte format (DATA). Each data transfer contains 8 bits. The number
of bytes transferred per transfer is unlimited. Data is transferred with the Most Significant bit
(MSb) first. If a receiver can’t receive another complete byte of data until it has performed
some other function, it can hold the clock line, SCL LOW to force the transmitter into a wait
state. Data transfer only continues when the receiver is ready for another byte and releases
the data line. If a slave receiver doesn’t acknowledge the slave address (i.e. it is not able to
receive because it is performing some real time function) the data line must be left HIGH by
the slave. The Master can then abort the transfer. A LOW to HIGH transition on the SDA line
while the SCL line is HIGH is defined as a STOP condition. Each data transfer must be
terminated by the generation of a STOP (SP) condition.
In order to read multiple bytes, it is necessary to assert the most significant bit of the subaddress field. In other words, SUB(7) must be equal to 1 while SUB(6-0) represents the
address of first register to read.
In the presented communication format MAK is Master Acknowledge and NMAK is No
Master Acknowledge.
4.1.2
I2C Subsequences
In order to better define subsequences and to clarify line SCL and SDA behavior, a
description containing discrete value of SCL and SDA will follow. In column there is the
value present on line SCL and SDA in discrete timing. These simple subsequences are
used to realize complex commands described in the following paragraph.
11/40
Digital interfaces
Figure 3.
AN2335
I2C Subsequences
ST: START condition
SCL
1111
SDA
1100
SR: Repeated START condition
SCL
1111
SDA
1100
SAD: Slave address (binary address: abcdefgh. In LIS302DL “abcdef” = “001110”)
SCL
00110
0110
0110
0110
0110
0110
0110
0110
SDA
0aaaa
bbbb
cccc
dddd
eeee
ffff
gggg
hhhh
Bit g=0 if SDO connected to GND, g=1 if SDO pad connected to Vdd
Bit h=0 => write, h=1 => read
SAK: Slave acknowledge (Z means high impedance)
SCL
0011
SDA (force)
ZZZZ
SDA (read)
XX00
Check that SDA is 0 after SCL=1
SUB: Sub address (binary address: a0cdefgh)
SCL
00110
0110
0110
0110
0110
0110
0110
0110
SDA
0aaaa
0000
cccc
dddd
eeee
ffff
gggg
hhhh
Bit a=0 => do not increment address in multiple mode
a=1 => increment address in multiple mode
DATA (Master): send DATA byte (binary number: abcdefgh)
SCL
00110
0110
0110
0110
0110
0110
0110
0110
SDA
0aaaa
bbbb
cccc
dddd
eeee
ffff
gggg
hhhh
DATA (Slave): read DATA byte (binary number: abcdefgh)
SCL
00110
0110
0110
0110
0110
0110
0110
0110
SDA (force)
ZZZZ
ZZZZ
ZZZZ
ZZZZ
ZZZZ
ZZZZ
ZZZZ
ZZZZ
SDA (read)
a
b
c
d
SP: STOP condition
SCL
1111
SDA
0011
MAK: Master Acknowledge
SCL
0011
SDA
0000
NMAK: No Master Acknowledge
12/40
SCL
0011
SDA
ZZZZ or 1111
e
f
g
h
AN2335
4.2
Digital interfaces
SPI bus interface
The LIS302DL SPI is a bus slave. The SPI allows to write and read the registers of the
device.
The Serial Interface interacts with the outside world with 4 wires: CS, SPC, SPDI and
SPDO.
4.2.1
Read & write protocol
Figure 4.
Read & write protocol
CS
SPC
SDI
DI7
RW
DI6
DI5
DI4
DI3
DI2
DI1
DI0
MS AD5 AD4 AD3 AD2 AD1 AD0
SDO
DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0
CS is the Chip Select and it is controlled by the SPI master. It goes low at the start of the
transmission and goes back high at the end. SPC is the Serial Port Clock and it is controlled
by the SPI master. It is stopped high when CS is high (no transmission). SDI and SDO are
respectively the Serial Port Data Input and Output. Those lines are driven at the falling edge
of SPC and should be captured at the rising edge of SPC.
Both the Read Register and Write Register commands are completed in 16 clocks pulses or
in multiple of 8 in case of multiple byte read/write. Bit duration is the time between two falling
edges of SPC. The first bit (bit 0) starts at the first falling edge of SPC after the falling edge
of CS while the last bit (bit 15, bit 23, ...) starts at the last falling edge of SPC just before the
rising edge of CS.
bit 0: RW bit. When 0, the data DI(7:0) is written into the device. When 1, the data DO(7:0)
from the device is read. In latter case, the chip will drive SDO at the start of bit 8.
bit 1: MS bit. When 0, the address will remain unchanged in multiple read/write commands.
When 1, the address will be auto incremented in multiple read/write commands.
bit 2-7: address AD(5:0). This is the address field of the indexed register.
bit 8-15: data DI(7:0) (write mode). This is the data that will be written into the device (MSb
first).
bit 8-15: data DO(7:0) (read mode). This is the data that will be read from the device (MSb
first).
In multiple read/write commands further blocks of 8 clock periods will be added. When MS
bit is 0 the address used to read/write data remains the same for every block. When MS bit
is 1 the address used to read/write data is incremented at every block.
The function and the behavior of SDI and SDO remain unchanged.
13/40
Digital interfaces
4.2.2
AN2335
SPI read
Figure 5.
SPI read protocol
CS
SPC
SDI
RW
MS AD5 AD4 AD3 AD2 AD1 AD0
SDO
DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0
The SPI Read command is performed with 16 clocks pulses. Multiple byte read command is
performed adding blocks of 8 clocks pulses at the previous one.
bit 0: READ bit. The value is 1.
bit 1: MS bit. When 0 do not increment address, when 1 increment address in multiple
reading.
bit 2-7: address AD(5:0). This is the address field of the indexed register.
bit 8-15: data DO(7:0) (read mode). This is the data that will be read from the device (MSb
first).
bit 16-... : data DO(...-8). Further data in multiple byte reading.
Figure 6.
Multiple bytes SPI read protocol (2 bytes example)
CS
SPC
SDI
RW
MS AD5 AD4 AD3 AD2 AD1 AD0
SDO
DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0 DO15 DO14 DO13 DO12 DO11 DO10 DO9 DO8
4.2.3
SPI Write
Figure 7.
SPI Write Protocol
CS
SPC
SDI
DI7 DI6 DI5 DI4 DI3 DI2 DI1 DI0
RW
MS AD5 AD4 AD3 AD2 AD1 AD0
14/40
AN2335
Digital interfaces
The SPI Write command is performed with 16 clocks pulses. Multiple byte write command is
performed adding blocks of 8 clocks pulses at the previous one.
bit 0: WRITE bit. The value is 0.
bit 1: MS bit. When 0 do not increment address, when 1 increment address in multiple
writing.
bit 2 -7: address AD(5:0). This is the address field of the indexed register.
bit 8-15: data DI(7:0) (write mode). This is the data that will be written inside the device
(MSb first).
bit 16-... : data DI(...-8). Further data in multiple byte writing.
Figure 8.
Multiple Bytes SPI Write Protocol (2 bytes example)
CS
SPC
SDI
DI7 DI6 DI5 DI4 DI3 DI2 DI1 DI0 DI15 DI14 DI13 DI12 DI11 DI10 DI9 DI8
RW
MS AD5 AD4 AD3 AD2 AD1 AD0
4.2.4
SPI Read in 3-wires mode
3-wires mode is entered by setting to 1 bit SIM (SPI Serial Interface Mode selection) in
CTRL_REG2.
Figure 9.
SPI Read Protocol In 3-wires Mode
CS
SPC
SDI
DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0
RW
MS AD5 AD4 AD3 AD2 AD1 AD0
The SPI Read command is performed with 16 clocks pulses:
bit 0: READ bit. The value is 1.
bit 1: MS bit. When 0 do not increment address, when 1 increment address in multiple
reading.
bit 2-7: address AD(5:0). This is the address field of the indexed register.
bit 8-15: data DO(7:0) (read mode). This is the data that will be read from the device (MSb
first).
Multiple read command is also available in 3-wires mode.
15/40
Registers description
AN2335
5
Registers description
5.1
Registers address map
The table given below provides a listing of the registers embedded in the device.
Table 4.
Registers address map
Name
Type
Register
Address
Hex
Reserved (Do not modify)
Who_Am_I
Default
Binary
00-0E
r
Reserved (Do not modify)
0F
Reserved
00 1111
00111011
10-1F
rw
20
10 0000
00000111
Ctrl_Reg2
rw
21
10 0001
00000000
Ctrl_Reg3
rw
22
10 0010
00000000
r
23
10 0011
dummy
Reserved (Do not modify)
24-26
r
27
10 0111
--
r
28
10 1000
Out_X
r
29
10 1001
--
r
2A
10 1010
Out_Y
r
2B
10 1011
--
r
2C
10 1100
Out_Z
r
2D
10 1101
FF_WU_CFG_1
00000000
Not Used
output
Not Used
output
Not Used
output
2E-2F
Reserved
rw
30
11 0000
00000000
r
31
11 0001
00000000
FF_WU_THS_1
rw
32
11 0010
00000000
FF_WU_DURATION_1
rw
33
11 0011
00000000
FF_WU_CFG_2
rw
34
11 0100
00000000
r
35
11 0101
00000000
FF_WU_THS_2
rw
36
11 0110
00000000
FF_WU_DURATION_2
rw
37
11 0111
00000000
FF_WU_SRC_1(ack1)
FF_WU_SRC_2 (ack2)
Reserved (Do not modify)
16/40
38-3F
Dummy register
Reserved
Status_Reg
Reserved (Do not modify)
Dummy register
Reserved
Ctrl_Reg1
HP_filter_reset
Comment
Reserved
AN2335
5.1.1
Registers description
Reserved Registers
Registers marked as reserved must not be changed. Random changes of the content of
those registers might cause permanent damages to the device.
5.1.2
Registers loaded at Boot
The LIS302DL is factory trimmed. The content of the registers that are loaded at boot must
not be changed. Their content is automatically restored when the device is powered-up.
17/40
About control registers
AN2335
6
About control registers
6.1
CTRL_REG1 (20h)
Control register #1.
DR
PD
FS
ST P
ST M
Zen
DR
Data rate selection. Default value: 0
(0: 100 Hz output data rate; 1: 400 Hz output data rate)
PD
Power Down Control. Default value: 0
(0: power down mode; 1: active mode)
FS
Full Scale selection. Default value: 0
(0: +/- 2g; 1: +/- 8g)
Yen
Xen
Self Test Enable. Default value: 00
(00: normal mode; 10: self test P; 01 self test M; 11: forbidden)
STP, STM
Zen
Z axis enable. Default value: 1
(0: Z axis disabled; 1: Z axis enabled)
Yen
Y axis enable. Default value: 1
(0: Y axis disabled; 1: Y axis enabled)
Xen
X axis enable. Default value: 1
(0: X axis disabled; 1: X axis enabled)
DR bit allows to select the data rate at which acceleration samples are produced. The
default value is 0 which corresponds to a data-rate of 100Hz. By changing the content of DR
to 1 the selected data-rate will be set equal to 400Hz.
PD bit allows to turn the device out of power-down mode. The device is in power-down mode
when PD= “0” (default value after boot). The device is in normal mode when PD is set to 1.
DR (DataRate)
PD (PowerDown)
Status
0
0
Power Down (Default)
0
1
Active (100Hz output)
1
0
Power Down
1
1
Active (400Hz output)
STP, STM bits are used to activate the self test function. When one of the bit is set to 1, an
output change will occur to the device outputs (refer to datasheet for specification) thus
allowing to check the functionality of the whole measurement chain. STP and STM move the
output in opposite directions.
Zen bit enables the generation of DataReady signal for Z-axis measurement channel when
set to 1. The default value is 1.
Yen bit enables the generation of DataReady signal for Y-axis measurement channel when
set to 1. The default value is 1.
Xen bit enables the generation of DataReady signal for X-axis measurement channel when
set to 1. The default value is 1.
18/40
AN2335
6.2
About control registers
CTRL_REG2 (21h)
Control register #2.
SIM
BOOT
SIM
BOOT
FDS
--
FDS
HP
FF_WU2
HP
FF_WU1
HP coeff2
SPI Serial Interface Mode selection. Default value: 0
(0: 4-wire interface; 1: 3-wire interface)
Reboot memory content. Default value: 0
(0: normal mode; 1: reboot memory content)
Filtered Data Selection. Default value: 0
(0: internal filter bypassed; 1: data from internal filter sent to output register)
HP FF_WU2
High Pass filter enabled for FreeFall/WakeUp # 2. Default value: 0
(0: filter bypassed; 1: filter enabled)
HP FF_WU1
High Pass filter enabled for Free-Fall/Wake-Up #1. Default value: 0
(0: filter bypassed; 1: filter enabled)
HP coeff2
HP coeff1
HP coeff1
High pass filter cut-off frequency configuration. Default value: 00
SIM bit selects the SPI Serial Interface Mode. When SIM is ‘0’ (default value) the 4-wire
interface mode is selected. The data coming from the device are sent to SDO pad. In 3-wire
interface mode output data are sent to SDA/SDI pad.
BOOT bit is used to refresh the content of internal registers stored in the flash memory
block. At the device power up the content of the flash memory block is transferred to the
internal registers related to trimming functions to permit a good behavior of the device itself.
If for any reason the content of trimming registers was changed it is sufficient to use this bit
to restore correct values. When BOOT bit is set to ‘1’ the content of internal flash is copied
inside corresponding internal registers and it is used to calibrate the device. These values
are factory trimmed, they are different for every accelerometer and normally they have not to
be changed. At the end of the boot process the BOOT bit is set again to ‘0’.
FDS bit enables (FDS=1) or bypass (FDS=0) the high pass filter in the signal chain of the
sensor.
HP FF_WU[2:1]. These bits enable (HP FF_WU=1) or bypass (HP FF_WU=0) the high pass
filter in interrupt generation blocks.
HP coeff[2:1]. These bits are used to configure high-pass filter cut-off frequency ft
accordingly to the table given below:
HPcoeff2,1
ft (Hz)
(DR=100 Hz)
ft (Hz)
(DR=400 Hz)
00
2
8
01
1
4
10
0.5
2
11
0.25
1
19/40
About control registers
AN2335
Figure 10 shows the block diagram of the digital processing chain and the related control
signals.
Figure 10. Digital Processing Chain Block Diagram
Regs Array
0
Offset
Adjustment
Block
Output regs
1
CTRL_REG3(FDS)
HP Filter
HP_FILTER_RESET
0
Interrupt Generator
(FF_WU 1)
SRC reg 1
1
CTRL_REG2(HP FF_WU1)
Digital Processing Chain
0
Interrupt Generator
(FF_WU 2)
SRC reg 2
1
CTRL_REG2(HP FF_WU2)
6.3
CTRL_REG3 (22h)
Control register #3.
IHL
IHL
PP_OD
I2CFG2
I2CFG1
I2CFG0
I1CFG2
I1CFG1
I1CFG0
Interrupt active high, low. Default value 0.
(0: active high; 1: active low)
PP_OD
Push-pull/Open Drain selection on interrupt pad. Default value 0.
(0: push-pull; 1: open drain)
I2CFG2,
I2CFG0
Interrupt 2 configuration bits. Default value 000.
(see table below)
I1CFG2,
I1CFG0
Interrupt 1 configuration bits. Default value 000.
(see table below)
IHL bit selects the polarity of the interrupt signal. When IHL is ‘0’ (default value) any interrupt
event will signalled with a logical 1.
PP_OD bit defines whether the interrupt pad has to work in Push-pull or in Open Drain
mode. The latter is specifically intended for wired-or connection of multiple interrupt signals
on the same interrupt line. The default value is ‘0’ which corresponds to push-pull mode.
I2CFG[2:0] and I1CFG[2:0] bit select which signal has to be sent out from the INT2 and
INT1 interrupt pads as described in the following table:
20/40
AN2335
About control registers
I2CFG2
I2CFG1
I2CFG0
INT2 Pin
I1CFG2
I1CFG1
I1CFG0
INT1 Pin
0
0
0
GND
0
0
1
FF_WU 1
0
1
0
FF_WU 2
0
1
1
FF_WU1 or FF_WU2
1
0
0
Dataready
1
1
1
--
Two completely independent interrupt blocks are available in LIS302DL: FF_WU1 and
FF_WU2. They can be configured using registers described in Section 8.
HP filtered data can be selected for further processing by the Interrupt Generator block
setting the desired values of HP FF_WU1 and HP FF_WU2 bits in CTRL_REG2. Default
value is '0' and corresponds to the use of non filtered data. The output of Interrupt Generator
block is used to load FF_WU_SRC_1 and FF_WU_SRC_2 registers.
21/40
Data and status registers
AN2335
7
Data and status registers
7.1
WHO_AM_I (0Fh)
Device identification register.
0
0
1
1
1
0
1
1
YDA
XDA
This register contains a device identifier which for LIS302DL is set to 3Bh.
7.2
STATUS_REG (27h)
Data output status register.
ZYXOR
ZYXOR
ZOR
YOR
XOR
ZYXDA
ZDA
X, Y and Z axes Data Overrun. Default value: 0
(0: no overrun has occurred;
1: new data has overwritten the previous one before it was read)
ZOR
Z axis Data Overrun. Default value: 0
(0: no overrun has occurred;
1: a new data for the Z-axis has overwritten the previous one)
YOR
Y axis Data Overrun. Default value: 0
(0: no overrun has occurred;
1: a new data for the Y-axis has overwritten the previous one)
XOR
X axis Data Overrun. Default value: 0
(0: no overrun has occurred;
1: a new data for the X-axis has overwritten the previous one)
ZYXDA
X, Y and Z axis new Data Available. Default value: 0
(0: a new set of data is not yet available; 1: a new set of data is available)
ZDA
Z axis new Data Available. Default value: 0
(0: a new data for the Z-axis is not yet available;
1: a new data for the Z-axis is available)
YDA
Y axis new Data Available. Default value: 0
(0: a new data for the Y-axis is not yet available;
1: a new data for the Y-axis is available)
XDA
X axis new Data Available. Default value: 0
(0: a new data for the X-axis is not yet available;
1: a new data for the X-axis is available)
ZYXOR is set to one whenever a new acceleration data is produced before completing the
retrieval of the previous set. When this occurs, the content of at least one acceleration data
register (i.e. OUTX, OUTY, OUTZ) has been overwritten. ZYXOR is cleared when the
acceleration data (OUTX, OUTY, OUTZ) of all the active channels are read.
22/40
AN2335
Data and status registers
ZOR is set to 1 whenever a new acceleration sample related to the Z-axis is generated
before the retrieval of the previous sample. When this occurs the previous sample is
overwritten. ZOR is cleared anytime OUTZ register is read.
YOR is set to 1 whenever a new acceleration sample related to the Y-axis is generated
before the retrieval of the previous sample. When this occurs the previous sample is
overwritten. YOR is cleared anytime OUTY_H register is read.
XOR is set to 1 whenever a new acceleration sample related to the X-axis is generated
before the retrieval of the previous sample. When this occurs the previous sample is
overwritten. XOR is cleared anytime OUTX_H register is read.
The ZYXDA bit signals that a new sample for all the enabled channels is available. ZYXDA
is cleared when the acceleration data (OUTX, OUTY, OUTZ) of all the enabled channels are
read.
ZDA is set to 1 whenever a new acceleration sample related to the Z-axis is available. ZDA
is cleared anytime OUTZ register is read. In order to trigger, the ZDA bit requires the Z axis
to be enabled (bit Zen=1 inside CTRL_REG1).
YDA is set to 1 whenever a new acceleration sample related to the Y-axis is available. YDA
is cleared anytime OUTY register is read. In order to trigger, the YDA bit requires the Y axis
to be enabled (bit Yen=1 inside CTRL_REG1).
XDA is set to 1 whenever a new acceleration sample related to the X-axis is available. XDA
is cleared anytime OUTX register is read. In order to trigger, the XDA bit requires the X axis
to be enabled (bit Xen=1 inside CTRL_REG1).
7.3
OUTX (29h)
X-axis output register.
XD7
7.4
XD6
XD5
XD4
XD3
XD2
XD1
XD0
YD5
YD4
YD3
YD2
YD1
YD0
ZD5
ZD4
ZD3
ZD2
ZD1
ZD0
OUTY (2Bh)
Y-axis output register.
.
YD7
7.5
YD6
OUTZ (2Dh)
Z-axis output register.
ZD7
ZD6
.
23/40
Free-Fall and Wake-Up Registers
8
AN2335
Free-Fall and Wake-Up Registers
The following sections describes the registers that are involved in the generation of the
interrupt signal associated to the inertial wake-up and free-fall events.
8.1
HP_FILTER_RESET (23h)
Dummy register. A reading at this address forces the high-pass filter to recover
instantaneously the dc level of the acceleration signal provided to its inputs. After the above
reading the output of the high-pass filter will be zero.
X
8.2
X
X
X
X
X
X
X
XHIE
XLIE
FF_WU_CFG_1 (30h)
Free-fall and wake-up configuration register for interrupt source 1.
.
AOI
24/40
LIR
ZHIE
ZLIE
YHIE
YLIE
AOI
And/Or combination of Interrupt events. Default value: 0
(0: OR combination of interrupt events; 1: AND combination of interrupt events)
LIR
Latch Interrupt request into FF_WU_SRC reg with the FF_WU_SRC reg cleared by
reading FF_WU_SRC_1 reg. Default value: 0
(0: interrupt request not latched; 1: interrupt request latched)
ZHIE
Enable interrupt generation on Z high event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value higher than preset threshold)
ZLIE
Enable interrupt generation on Z low event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value lower than preset threshold)
YHIE
Enable interrupt generation on Y high event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value higher than preset threshold)
YLIE
Enable interrupt generation on Y low event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value lower than preset threshold)
XHIE
Enable interrupt generation on X high event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value higher than preset threshold)
XLIE
Enable interrupt generation on X low event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value lower than preset threshold)
AN2335
Free-Fall and Wake-Up Registers
AOI bit allows to select between Wake-Up (OR combination of interrupt events) and FreeFall (AND combination of interrupt events) detection
LIR defines whether the configured interrupt event has to be latched by the device once it
has happened. The interrupt request is cleared by reading the related source reg
(FF_WU_SRC_1).
XHIE (YHIE, ZHIE) set an interrupt event to occur when the measured acceleration data on
X (Y, Z) channel is higher than the threshold set in FF_WU_THS_1 register.
XLIE (YLIE, ZLIE) set an interrupt event to occur when the measured acceleration data on X
(Y, Z) channel is lower than the threshold set in FF_WU_THS_1 register.
The threshold module which is used by the system to detect any free-fall or inertial wake-up
event is defined by FF_WU_THS_1. The threshold value is expressed over 7 bit as an
unsigned number and X, (Y, Z) high is true when the unsigned acceleration value of the X (Y,
Z) channel is higher than or egual to FF_WU_THS_1. Similarly, X, (Y, Z) low is true when
the unsigned acceleration value of the X (Y, Z) channel is lower than FF_WU_THS_1. Refer
to Figure 11 for more details.
Figure 11. FF_WU_CFG_1,2 High and Low value
+ Full Scale
X (Y, Z) high
Positive
acceleration
Threshold module
0 g level
X (Y, Z) low
Threshold module
Negative
acceleration
X (Y, Z) high
- Full Scale
8.3
FF_WU_SRC_1 (31h)
Free-fall and wake-up source register for interrupt 1. Read only register.
.
x
IA
IA
ZH
ZL
YH
YL
XH
XL
ZH
ZL
YH
YL
XH
XL
Interrupt Active. Default value: 0
(0: no interrupt has been generated;
1: one or more interrupt event has been generated)
Z High. Default value: 0
(0: no interrupt; 1: ZH event has occurred)
Z Low. Default value: 0
(0: no interrupt; 1: ZL event has occurred)
Y High. Default value: 0
(0: no interrupt; 1: YH event has occurred)
Y Low. Default value: 0
(0: no interrupt; 1: YL event has occurred)
X High. Default value: 0
(0: no interrupt; 1: XH event has occurred)
X Low. Default value: 0
(0: no interrupt; 1: XL event has occurred)
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Free-Fall and Wake-Up Registers
AN2335
This register keeps track of the acceleration event which is being triggering (or has
triggered, in case of LIR bit in FF_WU_SRC_1 reg set to 1) the interrupt signal. In particular
IA is equal to 1 when the combination of acceleration events specified in FF_WU_CFG_1
register is true. This bit is used for the generation of the interrupt signal associated to the
free-fall/wake-up events.
X, (Y, Z) high is true when the module of the acceleration value of the X (Y, Z) channel is
higher than the preset threshold which is defined as the concatenation of FF_WU_THS_1.
Similarly, X, (Y, Z) low is true when the module of the acceleration value of the X (Y, Z)
channel is lower than FF_WU_THS_1.
Reading at this address clears FF_WU_SRC_1 register and the FF_WU1 interrupt and
allows the refreshment of data in the FF_WU_SRC_1 register itself if the latched option was
chosen.
8.4
FF_WU_THS_1 (32h)
Free-fall, wake-up threshold for interrupt 1.
DCRM
THS6
THS5
THS4
THS3
THS2
DCRM
Duration counter reset mode selection. Default value: 0
(0: counter reset; 1: counter decremented)
THS6, THS0
Free-fall / wake-up Threshold: default value: 000 0000
THS1
THS0
DCRM bit allows to select the way in which the duration counter is reset. When DCRM is 0
the duration counter is reset immediately whenever the internal inertial event programmed
by the user is not active (Figure 12 part B) while it is decremented when DCRM is set to 1
(Figure 12 part C). The latter configuration allows to filter out spurious spikes which might
impair the recognition and validation of inertial events.
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Free-Fall and Wake-Up Registers
Figure 12. DCRM bit function
Duration
FreeFall event
Duration THS
Counter value
FreeFall Interrupt
Duration
FreeFall event
Duration THS
B
Counter value
FreeFall Interrupt
Duration
FreeFall event
Duration THS
C
Counter value
FreeFall Interrupt
8.5
FF_WU_DURATION_1 (33h)
Set the minimum duration of the free-fall, wake-up event that must be recognized by the
LIS302DL..
D7
D7, D0
D6
D5
D4
D3
D2
D1
D0
Duration value. Default value: 0000 0000
D7, D0 define the minimum duration of the programmed inertial event such as Free-Fall and
Wake-Up that must be recognized by the device. Duration step and maximum value depend
on the ODR chosen. For an output data rate of 400 Hz the register allows to set a duration
spanning from 0 to 637.5 msec with steps of 2.5 msec. Conversely when the output data
rate is set to 100 Hz it is possible to define an event duration spanning from 0 to 2.55 sec at
steps of 10 msec. The counter used to implement duration function is blocked when the LIR
bit in the configuration register is set to one and the interrupt event has occurred.
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Free-Fall and Wake-Up Registers
8.6
AN2335
FF_WU_CFG_2 (34h)
Free-fall and wake-up configuration register for interrupt source 2.
AOI
LIR
ZHIE
ZLIE
YHIE
YLIE
XHIE
XLIE
AOI
And/Or combination of Interrupt events. Default value: 0
(0: OR combination of interrupt events; 1: AND combination of interrupt events)
LIR
Latch Interrupt request into FF_WU_SRC reg with the FF_WU_SRC reg cleared by
reading FF_WU_SRC_1 reg. Default value: 0
(0: interrupt request not latched; 1: interrupt request latched)
ZHIE
Enable interrupt generation on Z high event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value higher than preset threshold)
ZLIE
Enable interrupt generation on Z low event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value lower than preset threshold)
YHIE
Enable interrupt generation on Y high event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value higher than preset threshold)
YLIE
Enable interrupt generation on Y low event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value lower than preset threshold)
XHIE
Enable interrupt generation on X high event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value higher than preset threshold)
XLIE
Enable interrupt generation on X low event. Default value: 0
(0: disable interrupt request;
1: enable interrupt request on measured accel. value lower than preset threshold)
Two structures can be used to generate interrupts. They have exactly the same
configuration capability and they are completely independent.
The interrupt result of each structure can be sent indifferently to INT1 or INT2 pin using
CTRL_Reg3 register.
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AN2335
8.7
Free-Fall and Wake-Up Registers
FF_WU_SRC_2 (35h)
Free-fall and wake-up source register for interrupt 2. Read only register. Refer to
FF_WU_SRC_1 for details.
x
IA
ZH
ZL
YH
YL
IA
Interrupt Active. Default value: 0
(0: no interrupt has been generated;
1: one or more interrupt event has been generated)
ZH
Z High. Default value: 0
(0: no interrupt; 1: ZH event has occurred)
ZL
Z Low. Default value: 0
(0: no interrupt; 1: ZL event has occurred)
YH
Y High. Default value: 0
(0: no interrupt; 1: YH event has occurred)
YL
Y Low. Default value: 0
(0: no interrupt; 1: YL event has occurred)
XH
X High. Default value: 0
(0: no interrupt; 1: XH event has occurred)
XL
X Low. Default value: 0
(0: no interrupt; 1: XL event has occurred)
XH
XL
Reading at this address clears FF_WU_SRC_2 register and the FF_WU2 interrupt and allows the refreshment of data in the FF_WU_SRC_2 register if the latched option was chosen.
8.8
FF_WU_THS_2 (36h)
Free-fall, wake-up threshold for interrupt source 2.
DCRM
THS6
THS5
THS4
THS3
THS2
DCRM
Duration counter reset mode selection. Default value: 0
(0: counter reset; 1: counter decremented)
THS6, THS0
Free-fall / wake-up Threshold: default value: 000 0000
THS1
THS0
DCRM bit and THS6 to THS0 behave exactly like bit in FF_WU_THS_1 but they are applied
to interrupt source 2.
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Free-Fall and Wake-Up Registers
8.9
AN2335
FF_WU_DURATION_2 (37h)
Set the minimum duration of the free-fall, wake-up event that must be recognized by the
LIS302DL.
D7
D7, D0
D6
D5
D4
Duration value. Default value: 0000 0000
Refer to FF_WU_DURATION_1 for details.
30/40
D3
D2
D1
D0
AN2335
Application Information
9
Application Information
9.1
START-UP SEQUENCE
Once the device is powered-up it automatically downloads the calibration coefficients from
the embedded flash to the internal registers. When the boot procedure is completed, i.e.
approximately after 3 milli-seconds, the device automatically enters power-down mode.
To turn-on the device and gather acceleration data it is necessary to write 47h inside the
CTRL_REG1. With this command the three acceleration channels (i.e. X, Y and Z axis) are
enabled and the Output Data Rate is set to 100 Hz.
9.2
READING ACCELERATION DATA
9.2.1
Using the Status Register
The device is provided with a STATUS_REG which should be polled to check when a new
set of data is available. The reading procedure should be the following:
1
read STATUS_REG
2
if STATUS_REG(3)=0 then goto 1
3
if STATUS_REG(7)=1 then some data have been overwritten
4
read OUTX
5
read OUTY
6
read OUTZ
7
data processing
8
goto 1
The check performed at step 3 allows to understand whether the reading rate is adequate
compared to the data production rate. In case one or more acceleration samples have been
overwritten by new data because of a reading rate too slow, the bit STATUS_REG(7) will be
set to 1.
The overrun bit are automatically cleared when all the data present inside the device have
been read and new data have not been produced in the meanwhile.
9.2.2
Using the Data-Ready Signal
The device may be configured to generate one HW signal (Data Ready) on either pin 8 or 9
to flag that a new set of measurement data is available for reading. This signal corresponds
to the ZYXDA bit present inside the STATUS_REG. The polarity of the signal is defined
through the IHL bit present inside the CTRL_REG3 and it is deasserted when the
acceleration data of all the enabled channels have been read. To enable Data Ready signal
on pin #8 (corresponding to INT1) it is necessary to set I1CFG[2:0] bit present inside the
CTRL_REG3 to 100. Conversely, to enable Data Ready signal on pin #9 (corresponding to
INT2) it is necessary to set I2CFG[2:0] bit present inside the CTRL_REG3 to 100.
31/40
Application Information
9.3
AN2335
Understanding acceleration data
The measured acceleration data are sent into OUTX, OUTY and OUTZ registers. The
acceleration values are expressed as a 2’s complement number. When the full-scale is set
to 2g, each LSB corresponds to 18mg.
The table below provides few basic examples of the data that will be read in the data
registers when the device is subject to a given acceleration. The values listed in the table
are given under the hypothesis of perfect device calibration (i.e no offset, no gain error, ....)
and rounded to the closest integer.
Table 5.
Output Data Registers content vs. Acceleration
FS bit = 0
FS bit = 1
Acceleration Values
Output Register Content
32/40
0g
00h
00h
350mg
14h
05h
1g
38h
0Eh
2g
6Fh
1Ch
-350mg
ECh
FBh
-1g
C8h
F2h
-2g
91h
E4h
AN2335
9.4
Application Information
Interrupt generation description
The LIS302DL provide two fully-programmable interrupt sources which may be configured
to trigger different inertial events. Among them it is worth mentioning the recognition of FreeFall and Wake-Up events. Whenever an interrupt condition is verified the interrupt signal is
asserted and reading either the FF_WU_SRC_1 or FF_WU_SRC_2 registers it is possible
to understand which condition has occurred.
The block diagram of the interrupt block is given in the pictures below.
Figure 13. Interrupt Generation Block Diagram
Ctrl_reg2(FDS)
0
ADC
Output Reg
HP filter
1
0
100/400Hz
FF_WU1
SRC1
1
Ph_Gen
Serial
Interface
(SPI
& I2C)
CFG 1
Ctrl_reg2(HP FF_WU1)
Ctrl_reg1(DR,PD)
0
FF_WU2
SRC2
1
CFG 2
Ctrl_reg2(HP FF_WU2)
Figure 14. Free-Fall, Wake-Up Interrupt Generator
THS reg
|b|>a?
WU
Accel_X
X_en
0
|b|>a?
Accel_Y
FF
|b|>a?
Accel_Z
1
Y_en
Z_en
FF_WU_CFG(AOI)
FF or WU interrupt generation is selected for each interrupt generation channel through AOI
bit in the corresponding FF_WU_CFG register. If AOI bit is ‘0’ signals coming from
comparators are put in logical or. Depending on values written in FF_WU_CFG_1 and
FF_WU_CFG_2 registers every time the value of at least one of the enabled axes exceeds
the threshold written in module in the corresponding FF_WU_THS_1 and FF_WU_THS_2
registers a FF, WU interrupt is generated. Otherwise if AOI bit is ‘1’ signals coming from
comparators are going into a “NAND” port. In this case an interrupt signal is generated
whenever the acceleration signal of all the enabled axes is below the threshold written in
FF_WU_THS_1 or FF_WU_THS_2 registers.
33/40
Application Information
AN2335
FF_WU_CFG(LIR) bit permits to decide if the interrupt request has to be latched or not. If
LIR bit is ‘0’ (default value) interrupt signal goes high when the interrupt condition is satisfied
and comes back low immediately if the interrupt condition is no more verified. Otherwise if
LIR bit is ‘1’ whenever a interrupt condition is applied the interrupt signal remains high even
if the condition comes back to non-interrupt status until a reading to FF_WU_SRC register is
performed.
The remaining bits of FF_WU_CFG register permits to decide on which axis the interrupt
decision has to be performed and on which direction the threshold has to be passed to
generate the interrupt request.
9.5
INERTIAL WAKE-UP
9.5.1
HP Filter Bypassed
This paragraph provides a basic algorithm which shows the practical use of the inertial
wake-up feature. In particular, with the code below, the device is configured to recognize
when the absolute acceleration along either X or Y axis exceeds a preset threshold (180mg
used in the example). The event which triggers the interrupt is latched inside the device
using FF_WU interrupt source 1 and its occurrence is signalled through the usage of the
INT2 pin.
34/40
1
write C7h into CTRL_REG1
// Turn on the sensor and set ODR=400Hz
2
write 00h into CTRL_REG2
// Default value: High Pass filter bypassed
3
write 08h into CTRL_REG3
// FF_WU1 interrupt sent to INT2 pin
4
write 0Ah into FF_WU_THS_1 reg
// Set wake-up threshold = 180 mg
5
write 00h into FF_WU_DURATION_1 reg
// No filtering/confirmation on the event
6
write 4Ah into FF_WU_CFG_1
// Configure desired wake-up event
7
poll INT2 pin; if INT2=0 then goto 7
// Poll INT2 pin waiting for the wake-up event
8
read FF_WU_SRC_1 reg
// Return the event that has triggered the
interrupt
// Clear interrupt request
9
(Wake-up event has occurred; insert your code
// Event handling
here)
10
goto 7
AN2335
9.5.2
Application Information
Using the HP Filter
The code provided below gives a basic routine which shows the practical use of the inertial
wake-up feature performed onto high-pass filtered data. In particular the device is
configured to recognize when the high-frequency component of the acceleration applied
along either X, Y or Z axis exceeds a preset threshold (180mg used in the example). The
event which triggers the interrupt is latched inside the device using FF_WU interrupt source
1 and its occurrence is signalled through the usage of the INT1 pin.
1
write C7h into CTRL_REG1
// Turn on the sensor and set ODR=400 Hz
2
write 04h into CTRL_REG2
// High Pass filter enabled on FF_WU1, fcutoff= 8Hz
3
write 01h into CTRL_REG3
// FF_WU1 interrupt sent to INT1 pin
4
write 0Ah into FF_WU_THS_1 reg
// Set wake-up threshold = 180 mg
5
write 00h into FF_WU_DURATION_1 reg
// No filtering/confirmation on the event
6
read HP_FILTER_RESET register
// Dummy read to force the HP filter to
// actual acceleration value
// (i.e. set reference acceleration/tilt value)
7
write 6Ah into FF_WU_CFG_1
// Configure desired wake-up event
8
poll INT1 pin; if INT1=0 then goto 7
// Poll INT1 pin waiting for the wake-up event
9
(Wake-up event has occurred; insert your code
// Event handling
here)
10
read FF_WU_SRC_1 reg
// Return the event that has triggered the
interrupt
// Clear interrupt request
11
(Insert your code here)
// Event handling
12
goto 8
At step 6, a dummy read at HP_FILTER_RESET register is performed to set the
current/reference acceleration/tilt state against which the device performed the threshold
comparison.
This read may be performed any time it is required to set the orientation/tilt of the device as
a reference state without waiting for the filter to settle.
35/40
Application Information
9.6
Free-Fall Detection
9.6.1
Roll function not used
AN2335
This paragraph provides the basics for the use of the free-fall detection feature. In particular
the SW routine that configures the device to detect free-fall events and to signal them is the
following:
1
write 47h into CTRL_REG1
// Turn on the sensor and set ODR=100 Hz
2
write 00h into CTRL_REG2
// Default value: High Pass filter bypassed
3
write 08h into CTRL_REG3
// FF_WU1 interrupt sent to INT2 pin
4
write 14h into FF_WU_THS_1 reg
// Set the free-fall threshold
5
write 09h into FF_WU_DURATION_1 reg
// Set minimum event duration to 90 msec
6
write D5h into FF_WU_CFG_1
// Configure free-fall recognition and latch
// interrupt request
7
poll INT2 pad; if INT2=0 then goto 7
// Poll INT2 pin waiting for the free-fall event
8
(Free-fall event has occurred; insert your code
here)
// Event handling
9
read FF_WU_SRC_1 register
// Clear interrupt request
10
goto 7
The code sample exploits a threshold set at 350mg for free-fall recognition and the event is
notified by the hardware signal INT2 pin. At step 5, the FF_WU_DURATION_1 register is
configured so to ignore events that are shorter than 9/ODR=9/100~90msec (ODR=output
data rate) in order to avoid false detections.
Once the free-fall event has occurred, a dummy read at FF_WU_SRC_1 reg clears the
request and the device is ready to recognize other events.
9.6.2
Roll function applied
Roll function can be added to free-fall condition recognition using both interrupt sources.
Interrupt signals can be sent to two different pins (INT1, INT2) or can be sent to the same so
that the first condition that is verified take control of the pin (logic “OR” of interrupt signals).
36/40
AN2335
9.7
Application Information
Output data rate selection and reading timing
The output data rate is user selectable through DR bit stored in CTRL_REG1 (20h) register.
At power-on-reset DR is reset to 0 thus providing a default output data rate set to 100 Hz.
The selectable output data rate are given in table below:
Table 6.
Output Data Rate
DR
Output data rate
0
100 Hz
1
400 Hz
The output data rate precision is related to internal oscillator or to external clock precision
and an error of +/- 10% should be taken in account.
The output data rate precision is related to internal oscillator or to external clock precision
and an error of +/- 10% should be taken in account.
A minimum reading period 150 μs shorter than the output data rate period is defined not to
loose any data produced. During this time period the reading of the data must be performed
and DataReady signal can be used as a trigger to begin the reading sequence. At the end of
the complete sequence DataReady signal goes down and the following rise edge advise
that new data are available. If this minimum reading frequency is not observed it is possible
to loose some data and the DataReady signal have no more the meaning of a trigger signal.
The status register can be used to infer whether an overrun condition has happened.
Figure 15. Reading Timing
T0
T1
T2
New data available
DataReady
Table 7.
Time
Timing Value to Avoid Loosing the Data
Description
T0
Data rate
T1
Reading period
T2
New data generation
Min
2.5 ms
Typ
Max
10 ms
T0-T2
150μs
37/40
Application Information
9.8
AN2335
Data ready vs. interrupt signal
The device is provided with two pins which can be activated to generate either the
DataReady or the interrupt signal. The functionality of the pins are selected acting on
interrupt configuration bit located in Ctrl_Reg3(2-0) for interrupt pin 1 (INT1) and in
Ctrl_Reg3(5-3) for interrupt pin 2 (INT2) accordingly to the block diagram given in Figure 16.
In particular the DataReady signal, stored in Status_Reg(3), which indicates when a new set
of acceleration data is ready, is made available by setting cfg bit to 100, while the interrupt
source 1 signal is carried out when cfg bit are set to 001 and interrupt source 2 when cfg bit
are set to 010. A Logic “OR” combination of interrupt source 1 and 2 can be sent to an
interrupt pin writing 011 in cfg bit.
Figure 16. Interrupt and dataready signal generation block diagram
DataReady DataReady signal
Signal
0
Generator
0 1 0 INT1 signal
Clock (100/400Hz)
Free-Fall,
Wake-Up
Interrupt
Generator
000
001
Interrupt Generator
(FF_WU_1, 2)
IA
(FF_WU_SRC_1)
011
Counter
ff_wu_duration
1
Clock (100/400Hz)
100
0
111
Latch
1
FF_WU_CFG1(LIR)
CTRL_REG3(2,1,0)
0
Free-Fall,
Wake-Up
Interrupt
Generator IA
Counter
ff_wu_duration
2
(FF_WU_SRC_2)
Latch
0
1
000
001
FF_WU_CFG2(LIR)
0 1 0 INT2 signal
011
100
111
CTRL_REG3(5,4,3)
The Data-ready signal is risen to 1 when a new set of acceleration data has been generated
and it is available for reading. The signal is reset after all the enabled channels are read
through the serial interface.
Figure 17. Data Ready Signal
ACCEL DATA
Accel. Sample #(N)
Accel. Sample #(N+1)
RDY
DATA READ
X
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Y
Z
X
Y
Z
AN2335
10
Revision history
Revision history
Table 8.
Document revision history
Date
Revision
Changes
03-Aug-2006
1
Initial release.
20-Oct-2006
2
Changes in the pages 8, 18 & 21.
39/40
AN2335
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