Sensors
14
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
. The detection status is
monitored by the detection source register $0A.
Figure 6. Double Pulse Detection
$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
$1D: Latency Time Value (Read/Write)
D7
D6
D5
D4
D3
D2
D1
D0
Reg $1D
LT[7]
LT[6]
LT[5]
LT[4]
LT[3]
LT[2]
LT[1]
LT[0]
Function
0
0
0
0
0
0
0
1
Default
$1E: Time Window for 2
nd
Pulse Value (Read/Write)
D7
D6
D5
D4
D3
D2
D1
D0
Reg $1E
TW[7]
TW[6]
TW[5]
TW[4]
TW[3]
TW[2]
TW[1]
TW[0]
Function
0
0
0
0
0
0
0
0
Default
Pulse Detection
Time Window
G
t h
G
Detection Source
Register
Latency Time Window
(2
nd
pulse ignored here)
Pulse Detection Time Window for
2
nd
pulse
Time
PDX or PDY or PDZ bit in Detection
source register is set.
Time Window >0 for 2 pulse detect
INT
Time
Time
Double Pulse Detection ($19 PDPL=0 indicating motion detection)
Time Window for 2
nd
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
