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
, under the
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
0
0
0
0
0
0
0
0
Default
D7
D6
D5
D4
D3
D2
D1
D0
Reg $19
--
--
--
--
--
DRVO
PDPL
LDPL
Function
0
0
0
0
0
0
0
0
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
0
0
0
0
0
0
0
0
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
0
0
0
0
0
0
0
1
Default
