MMA7455LR2 datasheet(14/35 Pages) FREESCALE

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Sensors

Freescale Semiconductor

MMA7455L

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

X OR Y OR Z > Threshold for Pulse Duration2 < PDTime2

For motion detection with double 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.

Then the Latency Time (time between pulses) must be set in Register $1D and then the Second Time Window must be set in

Register $1E for the time window of the second pulse. The pulse must be detected before the time window closes for the interrupt

to trigger.

When any of the events are detected, the interrupt pin (either INT1 or INT2) will go high. The interrupt pin assignment is set

up in Register $18, discussed in the Assigning, Clearing & Detecting Interrupts section on Page 15. The detection status is

monitored by the detection source register $0A.

Figure 6. Double Pulse Detection

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

Reg $1B

PDTH[7]

PDTH[6]

PDTH[5]

PDTH[4]

PDTH[3]

PDTH[2]

PDTH[1]

PDTH[0]

Function

00000000

Default

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

Reg $1C

PD[7]

PD[6]

PD[5]

PD[4]

PD[3]

PD[2]

PD[1]

PD[0]

Function

000

001

Default

$1D: Latency Time Value (Read/Write)

Reg $1D

LT[7]

LT[6]

LT[5]

LT[4]

LT[3]

LT[2]

LT[1]

LT[0]

Function

Default

$1E: Time Window for 2nd Pulse Value (Read/Write)

Reg $1E

TW[7]

TW[6]

TW[5]

TW[4]

TW[3]

TW[2]

TW[1]

TW[0]

Function

000

Default

Pulse Detection

Time Window

Detection Source

Latency Time Window

(2nd pulse ignored here)

Pulse Detection Time Window for

2nd pulse

Time

PDX or PDY or PDZ bit in Detection

source register is set.

Time Window >0 for 2 pulse detect

INT

Time

Double Pulse Detection ($19 PDPL=0 indicating motion detection)

Time Window for 2nd pulse $1E TW>0 indicating double pulse

*Note th ere is up to 1.6ms

delay on the interrupt signal

*Note there is up to 1.6ms

delay on the interrupt sign al

MMA7455LR2 Datasheet(PDF) 14 Page - Freescale Semiconductor, Inc

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