Sensors

12

Freescale Semiconductor

MMA7455L

PULSE DETECTION

In Pulse Mode, all functions can be active including measurements, level detections and pulse detection. There are two interrupt

pins available for detection of level and pulse conditions. The pulse detection has several timing windows associated with it. A

single pulse and a double pulse can be detected. Also freefall can be detected. The interrupt pins can be assigned to detect the

first pulse on one interrupt and the second pulse on the other interrupt. This is explained on Page 15, under the Assigning, Clear-

ing & Detecting Interrupts section.

By default all three axes are enabled and the detection range is 8g only. X and/or Y and/or Z can be disabled. There is a choice

between doing a detection for Motion detection vs. doing a detection for Freefall.

$18: Control 1 (Read/Write): Disable X, Y or Z for Pulse Detection

This allows the user to define how many axes to use for detection. All axes are enabled by default. To disable write 1

XDA: Disable X

YDA: Disable Y

ZDA: Disable Z.

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

PDPL

0: Pulse detection polarity is positive and detecting condition is OR 3 axes.

1: Pulse detection polarity is negative and detecting condition is AND 3 axes.

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

For motion detection with single pulse the device must be in pulse mode. PDPL in Register $19 =0 for “OR” motion condition.

The Pulse threshold must be set in Register $1B and the pulse duration time window must also be set using Register $1C. The

pulse must be detected before the time window closes for the interrupt to trigger.

D7

D6

D5

D4

D3

D2

D1

D0

Reg $18

DFBW

THOPT

ZDA

YDA

XDA

INTREG[1]

INTREG[0]

INTPIN

Function

00

000

000

Default

D7

D6

D5

D4

D3

D2

D1

D0

Reg $19

--

--

--

--

--

DRVO

PDPL

LDPL

Function

00000000

Default

$1B: Pulse Detection Threshold Limit Value (Read/Write)

D7

D6

D5

D4

D3

D2

D1

D0

Reg $1B

PDTH[7]

PDTH[6]

PDTH[5]

PDTH[4]

PDTH[3]

PDTH[2]

PDTH[1]

PDTH[0]

Function

00

00

00

00

Default

$1C: Pulse Duration Value (Read/Write)

D7

D6

D5

D4

D3

D2

D1

D0

Reg $1C

PD[7]

PD[6]

PD[5]

PD[4]

PD[3]

PD[2]

PD[1]

PD[0]

Function

00

000

001

Default