Sensors

Freescale Semiconductor

2

MMA7455L

Contents

ELECTRO STATIC DISCHARGE (ESD) ......................................................................................................................................6

PRINCIPLE OF OPERATION .......................................................................................................................................................8

FEATURES ...................................................................................................................................................................................8

Self-Test .........................................................................................................................................................................8

g-Select ...........................................................................................................................................................................9

Standby Mode .................................................................................................................................................................9

Measurement Mode ........................................................................................................................................................9

LEVEL DETECTION ...................................................................................................................................................................10

$18: Control 1 (Read/Write) Setting the Detection Axes for X, Y and Z .......................................................................10

$19: Control 2 (Read/Write) Motion Detection (OR Condition) or Freefall Detection (AND Condition) ........................10

$18: Control 1 (Read/Write): Setting the threshold to be an integer value or an absolute value ..................................10

$1A: Level Detection Threshold Limit Value (Read/Write) ...........................................................................................10

THRESHOLD DETECTION FOR MOTION AND FREEFALL CONDITIONS .............................................................................11

CASE 1: Motion Detection ............................................................................................................................................11

CASE 2: Motion Detection ............................................................................................................................................11

CASE 3: Freefall Detection ...........................................................................................................................................11

CASE 4: Freefall Detection ...........................................................................................................................................11

PULSE DETECTION ...................................................................................................................................................................12

$18: Control 1 (Read/Write): Disable X, Y or Z for pulse detection ..............................................................................12

$19: Control 2 (Read/Write): Motion Detection (OR condition) or Freefall Detection (AND condition) .........................12

CASE 1: Single Pulse Motion Detection: X or Y or Z > Pulse Threshold for Time < Pulse Duration ...........................12

CASE 2: Freefall Detection: X and Y and Z < Pulse Threshold for Time > Latency Time ............................................13

CASE 3: Double Pulse Detection: X OR Y OR Z > Threshold for Pulse Duration1 < PDTime1, Latency Time, AND .14

ASSIGNING, CLEARING & DETECTING INTERRUPTS ...........................................................................................................15

Clearing the Interrupt Pins: Register $17 ......................................................................................................................15

Detecting Interrupts ......................................................................................................................................................16

DIGITAL INTERFACE .................................................................................................................................................................16

I2C Slave Interface ........................................................................................................................................................16

SPI Slave Interface .......................................................................................................................................................18

BASIC CONNECTIONS ..............................................................................................................................................................19

Pin Descriptions ............................................................................................................................................................19

Recommended PCB Layout for Interfacing Accelerometer to Microcontroller .............................................................19

REGISTER DEFINITIONS ..........................................................................................................................................................21

SOLDERING AND MOUNTING GUIDELINES FOR THE LGA ACCELEROMETER SENSOR TO A PC BOARD ...................29