Sensors

Freescale Semiconductor

2

MMA7455L

Contents

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

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

FEATURES .................................................................................................................................................................................. 9

Self-Test ......................................................................................................................................................................... 9

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, ......... 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