Freescale MMA8451QT 3-axis, 14-bit/8-bit digital accelerometer Datasheet

Freescale Semiconductor
Technical Data
MMA8451Q
Rev 3, 09/2010
An
An Energy
Energy Efficient
Efficient Solution
Solution by
by Freescale
Freescale
3-Axis, 14-bit/8-bit
MMA8451Q
Digital Accelerometer
The MMA8451Q is a smart low-power, three-axis, capacitive micromachined
accelerometer with 14 bits of resolution. This accelerometer is packed with
embedded functions with flexible user programmable options, configurable to two
interrupt pins. Embedded interrupt functions allow for overall power savings
relieving the host processor from continuously polling data. There is access to
both low pass filtered data as well as high pass filtered data, which minimizes the
data analysis required for jolt detection and faster transitions. The device can be
configured to generate inertial wake-up interrupt signals from any combination of
the configurable embedded functions allowing the MMA8451Q to monitor events
and remain in a low power mode during periods of inactivity. The MMA8451Q is
available in a 3 mm x 3 mm x 1 mm QFN package.
MMA8451Q: 3-AXIS DIGITAL
ACCELEROMETER
±2g/±4g/±8g
Top and Bottom View
Features
16 PIN QFN
3 mm x 3 mm x 1 mm
CASE 2077-01
VDD
Top View
NC
•
•
•
•
•
•
•
1.95 V to 3.6 V supply voltage
1.6 V to 3.6 V interface voltage
±2g/±4g/±8g dynamically selectable full-scale
Output Data Rates (ODR) from 1.56 Hz to 800 Hz
99 μg/√Hz noise
14-bit and 8-bit digital output
I2C digital output interface (operates to 2.25 MHz with 4.7 kΩ pull-up)
2 programmable interrupt pins for 7 interrupt sources
3 embedded channels of motion detection
– Freefall or Motion Detection: 1 channel
– Pulse Detection: 1 channel
– Jolt Detection: 1 channel
Orientation (Portrait/Landscape) detection with programmable hysteresis
Automatic ODR change for Auto-WAKE and return to SLEEP
32 sample FIFO
High Pass Filter Data available per sample and through the FIFO
Self-Test
RoHS compliant
Current Consumption: 6 μA – 165 μA
NC
•
•
•
•
•
•
•
•
•
16
15
14
VDDIO
1
13
NC
BYP
2
12
GND
NC
3
11
INT1
SCL
4
MMA8451Q
10 GND
NC
SA0
SDA
Typical Applications
• E-Compass applications
GND 5
INT2
9
6
• Static orientation detection (Portrait/Landscape, Up/Down, Left/Right, Back/
7
8
Front position identification)
• Notebook, E-Reader and Laptop Tumble and Freefall Detection
Pin Connections
• Real-time orientation detection (virtual reality and gaming 3D user position
feedback)
• Real-time activity analysis (pedometer step counting, freefall drop detection for HDD, dead-reckoning GPS backup)
• Motion detection for portable product power saving (Auto-SLEEP and Auto-WAKE for cell phone, PDA, GPS, gaming)
• Shock and vibration monitoring (mechatronic compensation, shipping and warranty usage logging)
• User interface (menu scrolling by orientation change, tap detection for button replacement)
ORDERING INFORMATION
Part Number
Temperature Range
Package Description
MMA8451QT
-40°C to +85°C
QFN-16
Tray
MMA8451QR1
-40°C to +85°C
QFN-16
Tape and Reel
This document contains certain information on a new product.
Specifications and information herein are subject to change without notice.
© Freescale Semiconductor, Inc., 2010. All rights reserved.
Shipping
Contents
Application Notes for Reference .............................................................................................................................................. 6
1 Block Diagram and Pin Description .................................................................................................................................. 6
1.1 Block Diagram ............................................................................................................................................................. 6
Figure 1. Block Diagram ............................................................................................................................................. 6
1.2 Pin Description ............................................................................................................................................................ 6
Figure 2. Direction of the Detectable Accelerations .................................................................................................... 6
Figure 3. Landscape/Portrait Orientation .................................................................................................................... 7
Figure 4. Application Diagram ..................................................................................................................................... 7
Table 1. Pin Description .............................................................................................................................................. 8
1.3 Soldering Information .................................................................................................................................................. 8
2 Mechanical and Electrical Specifications ......................................................................................................................... 9
2.1 Mechanical Characteristics ......................................................................................................................................... 9
Table 2. Mechanical Characteristics ........................................................................................................................... 9
2.2 Electrical Characteristics ........................................................................................................................................... 10
Table 3. Electrical Characteristics............................................................................................................................. 10
2.3 I2C Interface Characteristic ....................................................................................................................................... 11
Table 4. I2C Slave Timing Values ............................................................................................................................. 11
Figure 5. I2C Slave Timing Diagram ......................................................................................................................... 12
2.4 Absolute Maximum Ratings ...................................................................................................................................... 12
Table 5. Maximum Ratings ....................................................................................................................................... 12
Table 6. ESD and Latch-Up Protection Characteristics ............................................................................................ 12
3 Terminology ...................................................................................................................................................................... 13
3.1 Sensitivity .................................................................................................................................................................. 13
3.2 Zero-g Offset ............................................................................................................................................................. 13
3.3 Self-Test .................................................................................................................................................................... 13
4 Modes of Operation .......................................................................................................................................................... 13
Figure 6. MMA8451Q Mode Transition Diagram ...................................................................................................... 13
Table 7. Mode of Operation Description ................................................................................................................... 13
5 Functionality ...................................................................................................................................................................... 14
5.1 Device Calibration ..................................................................................................................................................... 14
5.2 8-bit or 14-bit Data .................................................................................................................................................... 14
5.3 Internal FIFO Data Buffer .......................................................................................................................................... 14
5.4 Low Power Modes vs. High Resolution Modes ......................................................................................................... 15
5.5 Auto-WAKE/SLEEP Mode ........................................................................................................................................ 15
5.6 Freefall and Motion Detection ................................................................................................................................... 15
5.6.1
Freefall Detection ........................................................................................................................................... 15
5.6.2
Motion Detection ............................................................................................................................................ 15
5.7 Transient Detection ................................................................................................................................................... 16
5.8 Tap Detection ............................................................................................................................................................ 16
5.9 Orientation Detection ................................................................................................................................................ 16
Figure 7. Landscape/Portrait Orientation .................................................................................................................. 16
Figure 8. Illustration of Landscape to Portrait Transition .......................................................................................... 17
Figure 9. Illustration of Portrait to Landscape Transition .......................................................................................... 17
Figure 10. Illustration of Z-Tilt Angle Lockout Transition ........................................................................................... 17
5.10 Interrupt Register Configurations .............................................................................................................................. 18
Figure 11. System Interrupt Generation Block Diagram ........................................................................................... 18
5.11 Serial I2C Interface .................................................................................................................................................... 18
Table 8. Serial Interface Pin Description ................................................................................................................... 18
5.11.1 I2C Operation ................................................................................................................................................. 19
Table 9. I2C Address Selection Table ....................................................................................................................... 19
Single Byte Read ......................................................................................................................................................... 19
Multiple Byte Read ....................................................................................................................................................... 19
Single Byte Write ......................................................................................................................................................... 19
Multiple Byte Write ....................................................................................................................................................... 20
Table 10. I2C Device Address Sequence ................................................................................................................. 20
Figure 12. I2C Timing Diagram ................................................................................................................................. 20
MMA8451Q
2
Sensors
Freescale Semiconductor
6
Register Descriptions .......................................................................................................................................................21
Table 11. Register Address Map ...............................................................................................................................21
6.1 Data Registers ...........................................................................................................................................................22
F_MODE = 00: 0X00 STATUS: Data Status Register (Read Only) ....................................................................22
Table 12. STATUS Description .................................................................................................................................23
Data Registers: 0x01 OUT_X_MSB, 0x02 OUT_X_LSB, 0x03 OUT_Y_MSB, 0X04 OUT_Y_LSB ............................24
0x01 OUT_X_MSB: X_MSB Register (Read Only) .............................................................................................24
0x02 OUT_X_LSB: X_LSB Register (Read Only) ...............................................................................................24
0x03 OUT_Y_MSB: Y_MSB Register (Read Only) .............................................................................................24
0x04 OUT_Y_LSB: Y_LSB Register (Read Only) ...............................................................................................24
0x05 OUT_Z_MSB: Z_MSB Register (Read Only) .............................................................................................24
0x06 OUT_Z_LSB: Z_LSB Register (Read Only) ...............................................................................................24
6.2 32 Sample FIFO ........................................................................................................................................................24
F_MODE > 0 0x00: F_STATUS FIFO Status Register ................................................................................................24
0x00 F_STATUS: FIFO STATUS Register (Read Only) .....................................................................................24
Table 13. FIFO Flag Event Description .....................................................................................................................25
Table 14. FIFO Sample Count Description ...............................................................................................................25
0x09: F_SETUP FIFO Set-up Register ........................................................................................................................25
0x09 F_SETUP: FIFO Set-up Register (Read/Write) ..........................................................................................25
Table 15. F_SETUP Description ...............................................................................................................................25
0x0A: TRIG_CFG .........................................................................................................................................................26
0x0A: TRIG_CFG Trigger Configuration Register (Read/Write) ..........................................................................26
Table 16. Trigger Configuration Description ..............................................................................................................26
0x0B: SYSMOD System Mode Register ......................................................................................................................26
0x0B SYSMOD: System Mode Register (Read Only) .........................................................................................26
Table 17. SYSMOD Description ................................................................................................................................26
0x0C: INT_SOURCE System Interrupt Status Register ...............................................................................................27
Table 18. INT_SOURCE Description ........................................................................................................................27
0x0D: WHO_AM_I Device ID Register .........................................................................................................................28
0x0D: WHO_AM_I Device ID Register (Read Only) ............................................................................................28
0x0E: XYZ_DATA_CFG Register ................................................................................................................................28
0x0E: XYZ_DATA_CFG (Read/Write) .................................................................................................................28
Table 19. XYZ Data Configuration Descriptions ........................................................................................................28
Table 20. Full Scale Range .......................................................................................................................................28
0x0F: HP_FILTER_CUTOFF High Pass Filter Register ..............................................................................................28
0x0F HP_FILTER_CUTOFF: High Pass Filter Register (Read/Write) ................................................................28
Table 21. High Pass Filter Cut-off Register Descriptions ..........................................................................................28
Table 22. High Pass Filter Cut-off Options ................................................................................................................29
6.3 Portrait/ Landscape Embedded Function Registers ..................................................................................................29
0x10: PL_STATUS Portrait/Landscape Status Register ..............................................................................................29
0x10 PL_STATUS Register (Read Only) ............................................................................................................29
Table 23. PL_STATUS Register Description ............................................................................................................29
0x11 Portrait/Landscape Configuration Register .........................................................................................................30
0x11 PL_CFG Register (Read/Write ...................................................................................................................30
Table 24. PL_CFG Description .................................................................................................................................30
0x12 Portrait/Landscape Debounce Counter ...............................................................................................................30
0x12 PL_COUNT Register (Read/Write) .............................................................................................................30
Table 25. PL_COUNT Description ............................................................................................................................30
Table 26. PL_COUNT Relationship with the ODR ....................................................................................................30
0x13: PL_BF_ZCOMP Back/Front and Z Compensation Register ..............................................................................30
0x13: PL_BF_ZCOMP Register (Read/Write) .....................................................................................................30
Table 27. PL_BF_ZCOMP Description .....................................................................................................................30
Table 28. Z-Lock Threshold Angles ..........................................................................................................................31
Table 29. Back/Front Orientation Definition ..............................................................................................................31
0x14: P_L_THS_REG Portrait/Landscape Threshold and Hysteresis Register ...........................................................31
0x14: P_L_THS_REG Register (Read/Write) ......................................................................................................31
Table 30. P_L_THS_REG Description ......................................................................................................................31
Table 31. Threshold Angle Thresholds Look-up Table .............................................................................................31
Table 32. Trip Angles with Hysteresis for 45° Angle .................................................................................................31
MMA8451Q
Sensors
Freescale Semiconductor
3
6.4
Motion and Freefall Embedded Function Registers .................................................................................................. 32
Mode 1: Freefall Detection with ELE = 0, OAE = 0 ...................................................................................................... 32
Mode 2: Freefall Detection with ELE = 1, OAE = 0 ...................................................................................................... 32
Mode 3: Motion Detection with ELE = 0, OAE = 1 ....................................................................................................... 32
Mode 4: Motion Detection with ELE = 1, OAE = 1 ....................................................................................................... 32
0x15 FF_MT_CFG Freefall/Motion Configuration Register ........................................................................................ 33
0x15 FF_MT_CFG Register (Read/Write) .......................................................................................................... 33
Table 33. FF_MT_CFG Description ......................................................................................................................... 33
Figure 13. FF_MT_CFG High and Low g Level ........................................................................................................ 33
0x16 FF_MT_SRC Freefall/Motion Source Register ................................................................................................... 33
0x16: FF_MT_SRC Freefall and Motion Source Register (Read Only) .............................................................. 33
Table 34. Freefall/Motion Source Description .......................................................................................................... 34
0x17: FF_MT_THS Freefall and Motion Threshold Register ....................................................................................... 34
0x17 FF_MT_THS Register (Read/Write) ........................................................................................................... 34
Table 35. FF_MT_THS Description .......................................................................................................................... 34
0x18 FF_MT_COUNT Debounce Register ................................................................................................................. 35
0x18 FF_MT_COUNT_Register (Read/Write) .................................................................................................... 35
Table 36. FF_MT_COUNT Description ..................................................................................................................... 35
Table 37. FF_MT_COUNT Relationship with the ODR ............................................................................................ 35
Figure 14. DBCNTM Bit Function ............................................................................................................................. 36
6.5 Transient (HPF) Acceleration Detection ................................................................................................................... 37
0x1D: Transient_CFG Register ................................................................................................................................... 37
0x1D TRANSIENT_ CFG Register (Read/Write) ................................................................................................ 37
Table 38. TRANSIENT_ CFG Description ................................................................................................................ 37
0x1E TRANSIENT_SRC Register ............................................................................................................................... 37
0x1E TRANSIENT_SRC Register (Read Only) .................................................................................................. 37
Table 39. TRANSIENT_SRC Description ................................................................................................................. 37
0x1F TRANSIENT_THS Register ................................................................................................................................ 38
0x1F TRANSIENT_THS Register (Read/Write) .................................................................................................. 38
Table 40. TRANSIENT_THS Description ................................................................................................................. 38
0x20 TRANSIENT_COUNT ......................................................................................................................................... 38
0x20 TRANSIENT_COUNT Register (Read/Write) ............................................................................................ 38
Table 41. TRANSIENT_COUNT Description ............................................................................................................ 38
Table 42. TRANSIENT_COUNT Relationship with the ODR .................................................................................... 38
6.6 Single, Double and Directional Tap Detection Registers .......................................................................................... 39
0x21: PULSE_CFG Pulse Configuration Register ....................................................................................................... 39
0x21 PULSE_CFG Register (Read/Write) .......................................................................................................... 39
Table 43. PULSE_CFG Description .......................................................................................................................... 39
0x22: PULSE_SRC Pulse Source Register ................................................................................................................. 39
0x22 PULSE_SRC Register (Read Only) ........................................................................................................... 39
Table 44. PULSE_SRC Description .......................................................................................................................... 39
0x23 - 0x25: PULSE_THSX, Y, Z Pulse Threshold for X, Y & Z Registers ................................................................. 40
0x23 PULSE_THSX Register (Read/Write) ........................................................................................................ 40
Table 45. PULSE_THSX Description ........................................................................................................................ 40
0x24 PULSE_THSY Register (Read/Write) ........................................................................................................ 40
Table 46. PULSE_THSY Description ........................................................................................................................ 40
0x25 PULSE_THSZ Register (Read/Write) ........................................................................................................ 40
Table 47. PULSE_THSZ Description ........................................................................................................................ 40
0x26: PULSE_TMLT Pulse Time Window 1 Register .................................................................................................. 40
0x26 PULSE_TMLT Register (Read/Write) ........................................................................................................ 40
Table 48. PULSE_TMLT Description ........................................................................................................................ 40
Table 49. Time Step for PULSE Time Limit (Reg 0x0F) Pulse_ LPF_EN = 1 .......................................................... 40
Table 50. Time Step for PULSE Time Limit (Reg 0x0F) Pulse_LPF_EN = 0 ........................................................... 41
0x27: PULSE_LTCY Pulse Latency Timer Register .................................................................................................... 41
0x27 PULSE_LTCY Register (Read/Write) ......................................................................................................... 41
Table 51. PULSE_LTCY Description ........................................................................................................................ 41
Table 52. Time Step for PULSE Latency @ ODR and Power Mode (Reg 0x0F) Pulse_ LPF_EN = 1 .................... 41
Table 53. Time Step for PULSE Latency @ ODR and Power Mode (Reg 0x0F) Pulse_ LPF_EN = 0 .................... 41
0x28 PULSE_WIND Register (Read/Write) ................................................................................................................. 42
Table 54. PULSE_WIND Description ........................................................................................................................ 42
Table 55. Time Step for PULSE Detection Window @ ODR and Power Mode (Reg 0x0F) Pulse_ LPF_EN = 1 .... 42
Table 56. Time Step for PULSE Detection Window @ ODR and Power Mode (Reg 0x0F) Pulse_ LPF_EN = 0 ..... 42
MMA8451Q
4
Sensors
Freescale Semiconductor
6.7
Auto-WAKE/SLEEP Detection ..................................................................................................................................43
0x29 ASLP_COUNT Register (Read/Write) ........................................................................................................43
Table 57. ASLP_COUNT Description .......................................................................................................................43
Table 58. ASLP_COUNT Relationship with ODR .....................................................................................................43
Table 59. SLEEP/WAKE Mode Gates and Triggers .................................................................................................43
6.8 Control Registers .......................................................................................................................................................44
0x2A: CTRL_REG1 System Control 1 Register ...........................................................................................................44
0x2A CTRL_REG1 Register (Read/Write) ..........................................................................................................44
Table 60. CTRL_REG1 Description ..........................................................................................................................44
Table 61. SLEEP Mode Rate Description .................................................................................................................44
Table 62. System Output Data Rate Selection ..........................................................................................................44
Table 63. Full Scale Selection ...................................................................................................................................44
0x2B: CTRL_REG2 System Control 2 Register ...........................................................................................................45
0x2B CTRL_REG2 Register (Read/Write) ..........................................................................................................45
Table 64. CTRL_REG2 Description ..........................................................................................................................45
Table 65. MODS Oversampling Modes .....................................................................................................................45
Table 66. MODS Oversampling Modes Current Consumption and Averaging Values at each ODR .......................45
0x2C: CTRL_REG3 Interrupt Control Register ............................................................................................................46
0x2C CTRL_REG3 Register (Read/Write) ..........................................................................................................46
Table 67. CTRL_REG3 Description ..........................................................................................................................46
0x2D: CTRL_REG4 Register (Read/Write) ..................................................................................................................46
0x2D CTRL_REG4 Register (Read/Write) ..........................................................................................................46
Table 68. Interrupt Enable Register Description .......................................................................................................46
0x2E CTRL_REG5 Register (Read/Write) ...................................................................................................................47
0x2E: CTRL_REG5 Interrupt Configuration Register ..........................................................................................47
Table 69. Interrupt Configuration Register Description .............................................................................................47
6.9 User Offset Correction Registers ..............................................................................................................................47
0x2F: OFF_X Offset Correction X Register ..................................................................................................................47
0x2F OFF_X Register (Read/Write) ....................................................................................................................47
Table 70. OFF_X Description ....................................................................................................................................47
0x30: OFF_Y Offset Correction Y Register ..................................................................................................................47
0x30 OFF_Y Register (Read/Write) ....................................................................................................................47
Table 71. OFF_Y Description ....................................................................................................................................47
0x31: OFF_Z Offset Correction Z Register ..................................................................................................................47
0x31 OFF_Z Register (Read/Write) .....................................................................................................................47
Table 72. OFF_Z Description ....................................................................................................................................47
Table 73. MMA8451Q Register Map .........................................................................................................................48
Table 74. Accelerometer Output Data .......................................................................................................................49
Package Dimensions................................................................................................................................................................50
MMA8451Q
Sensors
Freescale Semiconductor
5
Application Notes for Reference
The following is a list of Freescale Application Notes written for the MMA8451, 2, 3Q:
• AN4068, Embedded Orientation Detection Using the MMA8451, 2, 3Q
• AN4069, Offset Calibration of the MMA8451, 2, 3Q
• AN4070, Motion and Freefall Detection Using the MMA8451, 2, 3Q
• AN4071, High Pass Data and Functions Using the MMA8451, 2,3Q
• AN4072, MMA8451, 2, 3Q Single/Double and Directional Tap Detection
• AN4073, Using the 32 Sample First In First Out (FIFO) in the MMA8451Q
• AN4074, Auto-Wake/Sleep Using the MMA8451, 2, 3Q
• AN4075, How Many Bits are Enough? The Trade-off Between High Resolution and Low Power Using Oversampling Modes
• AN4076, Data Manipulation and Basic Settings of the MMA8451, 2, 3Q
• AN4077, MMA8451, 2, 3Q Design Checklist and Board Mounting Guidelines
1
Block Diagram and Pin Description
1.1
Block Diagram
Internal
OSC
X-axis
Transducer
VDD
VDDIO
INT2
Embedded
DSP
Functions
14-bit
ADC
C to V
Converter
Y-axis
Transducer
VSS
INT1
Clock
GEN
I2 C
SDA
SCL
Z-axis
Transducer
32 Data Point
Configurable
FIFO Buffer
with Watermark
Freefall
and Motion
Detection
Transient
Detection
(i.e., fast motion,
jolt)
Enhanced
Orientation with
Hysteresis
and Z-lockout
Shake Detection
through
Motion
Threshold
Single, Double
& Directional Tap
Detection
Auto-WAKE/Auto-SLEEP Configurable with debounce counter and multiple motion interrupts for control
MODE Options
Low Power
Low Noise + Power
High Resolution
Normal
ACTIVE Mode
MODE Options
Low Power
Low Noise + Power
High Resolution
Normal
ACTIVE Mode
WAKE
SLEEP
Auto-WAKE/SLEEP
Figure 1. Block Diagram
1.2
Pin Description
Z
Earth Gravity
X
1
Y
(TOP VIEW)
DIRECTION OF THE
DETECTABLE ACCELERATIONS
13
1
9
5
(BOTTOM VIEW)
Figure 2. Direction of the Detectable Accelerations
MMA8451Q
6
Sensors
Freescale Semiconductor
Figure 3 shows the device configuration in the 6 different orientation modes. These orientations are defined as the following:
PU = Portrait Up, LR = Landscape Right, PD = Portrait Down, LL = Landscape Left, BACK and FRONT side views. There are
several registers to configure the orientation detection and are described in detail in the register setting section.
Top View
PU
Pin 1
Earth Gravity
Side View
LL
LR
Xout @ 0g
Yout @ -1g
Zout @ 0g
BACK
Xout @ 0g
Yout @ 0g
Zout @ -1g
PD
Xout @ -1g
Yout @ 0g
Zout @ 0g
Xout @ 1g
Yout @ 0g
Zout @ 0g
FRONT
Xout @ 0g
Yout @ 0g
Zout @ 1g
Xout @ 0g
Yout @ 1g
Zout @ 0g
Figure 3. Landscape/Portrait Orientation
1.6V - 3.6V
Interface Voltage
1.95V - 3.6V
VDD
4.7μF
0.1μF
NC
4
SCL
5
GND
VDD
3
NC
BYP
MMA8451Q
NC
4.7kΩ
0.1μF
2
14
SA0
4.7kΩ
VDDIO
VDDIO
15
SDA
VDDIO
1
NC
16
6
7
8
NC
13
GND
12
INT1
11
GND
10
INT2
9
INT1
SCL
INT2
SA0
SDA
Figure 4. Application Diagram
MMA8451Q
Sensors
Freescale Semiconductor
7
Table 1. Pin Description
Pin #
Pin Name
1
VDDIO
2
Description
Pin Status
Internal Power Supply (1.62 V - 3.6 V)
Input
BYP
Bypass capacitor (0.1 μF)
Input
3
NC
Leave open. Do not connect
4
SCL
I2C Serial Clock
5
GND
Connect to Ground
2
Open
Open Drain
Input
Open Drain
6
SDA
I C Serial Data
7
SA0
I2C Least Significant Bit of the Device I2C Address
Input
8
NC
Internally not connected (can be GND or VDD)
Input
9
INT2
Inertial Interrupt 2
10
GND
Connect to Ground
Output
11
INT1
Inertial Interrupt 1
12
GND
Connect to Ground
Input
13
NC
Internally not connected (can be GND or VDD)
Input
14
VDD
Power Supply (1.95 V - 3.6 V)
Input
15
NC
Internally not connected (can be GND or VDD)
Input
16
NC
Internally not connected (can be GND or VDD)
Input
Input
Output
The device power is supplied through VDD line. Power supply decoupling capacitors (100 nF ceramic plus 4.7 µF bulk, or a
single 4.7 µF ceramic) should be placed as near as possible to the pins 1 and 14 of the device.
The control signals SCL, SDA, and SA0 are not tolerant of voltages more than VDDIO + 0.3 V. If VDDIO is removed, the control
signals SCL, SDA, and SA0 will clamp any logic signals with their internal ESD protection diodes.
The functions, the threshold and the timing of the two interrupt pins (INT1 and INT2) are user programmable through the I2C
interface. The SDA and SCL I2C connections are open drain and therefore require a pull-up resistor as shown in the application
diagram in Figure 4.
1.3
Soldering Information
The QFN package is compliant with the RoHS standard. Please refer to AN4077.
MMA8451Q
8
Sensors
Freescale Semiconductor
2
Mechanical and Electrical Specifications
2.1
Mechanical Characteristics
Table 2. Mechanical Characteristics @ VDD = 2.5 V, VDDIO = 1.8 V, T = 25°C unless otherwise noted.
Parameter
Test Conditions
Symbol
Min
FS[1:0] set to 00
2g Mode
Measurement Range(1)
Sensitivity
FS[1:0] set to 01
4g Mode
Typ
FS
±4
±8
FS[1:0] set to 00
2g Mode
4096
So
g
2048
FS[1:0] set to 10
8g Mode
Sensitivity Accuracy(2)
Unit
±2
FS[1:0] set to 10
8g Mode
FS[1:0] set to 01
4g Mode
Max
counts/g
1024
Soa
±2.5
%
TCSo
±0.008
%/°C
FS[1:0] set to 00
2g Mode
Sensitivity Change vs. Temperature
FS[1:0] set to 01
4g Mode
FS[1:0] set to 10
8g Mode
Zero-g Level Offset Accuracy(3)
FS[1:0] 2g, 4g, 8g
TyOff
±20
mg
Zero-g Level Offset Accuracy Post Board Mount(4)
FS[1:0] 2g, 4g, 8g
TyOffPBM
±30
mg
-40°C to 85°C
TCOff
±0.15
mg/°C
Zero-g Level Change vs. Temperature
Non-Linearity
Best Fit Straight Line
Self-Test Output Change(5)
X
Y
Z
Over ±2g range
±8g range
FS[1:0] set to 0
4g Mode
±0.2
NL
%FS
±0.5
+181
+255
+1680
Vst
ODR Accuracy
2 MHz Clock
LSB
%
±2
Output Data Bandwidth
BW
ODR/3
ODR/2
Hz
Output Noise
Normal Mode ODR = 400 Hz
Noise
126
µg/√Hz
Output Noise Low Noise Mode(1)
Normal Mode ODR = 400 Hz
Noise
99
µg/√Hz
Operating Temperature Range
Top
-40
+85
°C
1. Dynamic Range is limited to 4g when the Low Noise bit in Register 0x2A, bit 2 is set.
2. Sensitivity remains in spec as stated, but changing Oversampling mode to Low Power causes 3% sensitivity shift. This behavior is also seen
when changing from 800 Hz to any other data rate in the Normal, Low Noise + Low Power or High Resolution mode.
3. Before board mount.
4. Post Board Mount Offset Specifications are based on an 8 Layer PCB, relative to 25°C.
5. Self-Test is one direction only.
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2.2
Electrical Characteristics
Table 3. Electrical Characteristics @ VDD = 2.5 V, VDDIO = 1.8 V, T = 25°C unless otherwise noted.
Parameter
Test Conditions
Supply Voltage
Interface Supply Voltage
Low Power Mode
Symbol
Min
Typ
Max
Unit
VDD(1)
1.95
2.5
3.6
V
VDDIO(1)
1.62
1.8
3.6
V
ODR = 1.56 Hz
6
ODR = 6.25 Hz
6
ODR = 12.5 Hz
6
ODR = 50 Hz
14
ODR = 100 Hz
IddLP
ODR = 200 Hz
Normal Mode
44
ODR = 400 Hz
85
ODR = 800 Hz
165
ODR = 1.56 Hz
24
ODR = 6.25 Hz
24
ODR = 12.5 Hz
24
ODR = 50 Hz
ODR = 100 Hz
24
Idd
85
ODR = 400 Hz
165
ODR = 800 Hz
165
VDD = 2.5 V
Idd Boot
Value of Capacitor on BYP Pin
-40°C 85°C
Cap
VDD = 2.5 V, VDDIO = 1.8 V
STANDBY Mode
IddStby
Digital High Level Input Voltage
SCL, SDA, SA0
VIH
Digital Low Level Input Voltage
SCL, SDA, SA0
VIL
μA
44
ODR = 200 Hz
Current during Boot Sequence, 0.5 mSec max
duration using recommended Bypass Cap
STANDBY Mode Current @25°C
μA
24
75
1
μA
100
470
nF
1.8
5
μA
V
0.75*VDDIO
0.3*VDDIO
High Level Output Voltage
INT1, INT2
IO = 500 μA
VOH
Low Level Output Voltage
INT1, INT2
IO = 500 μA
VOL
0.1*VDDIO
Low Level Output Voltage
SDA
IO = 500 μA
VOLS
0.1*VDDIO
Power on Ramp Time
Time from VDDIO on and VDD > Vmin until
ready for operation
V
0.9*VDDIO
0.001
I2C
Cbyp = 100 nF
BT
—
V
V
V
1000
ms
500
µs
350
Turn-on time (STANDBY to ACTIVE)
Ton
2/ODR + 1 ms
s
Turn-on time (Power Down to ACTIVE Mode)
Ton
2/ODR + 2 ms
s
Operating Temperature Range
Top
-40
+85
°C
1. There is no requirement for power supply sequencing. The VDDIO input voltage can be higher than the VDD input voltage.
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2.3
I2C Interface Characteristic
Table 4. I2C Slave Timing Values(1)
Parameter
Symbol
I2C Fast Mode
Min
Max
0
0
0
0
0
2.250
100
Non-functional
4.50
750
Unit
SCL Clock Frequency
Pull-up = 4.7 kΩ, Cb = 20 pF
Pull-up = 4.7 kΩ, Cb = 40 pF
Pull-up = 4.7 kΩ, Cb = 400 pF
Pull-up = 1 kΩ, Cb = 20 pF
Pull-up = 1 kΩ, Cb = 400 pF
fSCL
Bus Free Time between STOP and START Condition
tBUF
1.3
μs
Repeated START Hold Time
tHD;STA
0.6
μs
Repeated START Set-up Time
tSU;STA
0.6
μs
STOP Condition Set-up Time
tSU;STO
0.6
μs
SDA Data Hold Time(2)
tHD;DAT
50
SDA Valid Time
(4)
tVD;DAT
SDA Valid Acknowledge Time
(5)
tVD;ACK
(3)
MHz
kHz
—
MHz
kHz
μs
0.9
(3)
μs
0.9
(3)
μs
tSU;DAT
100(6)
ns
SCL Clock Low Time
tLOW
4.7
μs
SCL Clock High Time
tHIGH
4
μs
SDA Set-up Time
SDA and SCL Rise Time
SDA and SCL Fall Time
(7) (8)
Pulse width of spikes on SDA and SCL that must be suppressed by input filter
tr
1000
ns
tf
300
ns
tSP
50
ns
1. All values referred to VIH (min) and VIL (max) levels.
2. tHD;DAT is the data hold time that is measured from the falling edge of SCL, applies to data in transmission and the acknowledge.
3. The maximum tHD;DAT could be 3.45 μs and 0.9 μs for Standard mode and Fast mode, but must be less than the maximum of tVD;DAT or tVD;ACK
by a transition time.
4. tVD;DAT = time for Data signal from SCL LOW to SDA output (HIGH or LOW, depending on which one is worse).
5. tVD;ACK = time for Acknowledgement signal from SCL LOW to SDA output (HIGH or LOW, depending on which one is worse).
6. A Fast mode I2C device can be used in a Standard mode I2C system, but the requirement tSU;DAT 250 ns must then be met. This will
automatically be the case if the device does not stretch the LOW period of the SCL signal. If such a device does stretch the LOW period of the
SCL signal, it must output the next data bit to the SDA line tr(max) + tSU;DAT = 1000 + 250 = 1250 ns (according to the Standard mode I2C
specification) before the SCL line is released. Also the acknowledge timing must meet this set-up time
7. Cb = total capacitance of one bus line in pF.
8. The maximum tf for the SDA and SCL bus lines is specified at 300 ns. The maximum fall time for the SDA output stage tf is specified at 250 ns.
This allows series protection resistors to be connected in between the SDA and the SCL pins and the SDA/SCL bus lines without exceeding
the maximum specified tf.
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11
Figure 5. I2C Slave Timing Diagram
2.4
Absolute Maximum Ratings
Stresses above those listed as “absolute maximum ratings” may cause permanent damage to the device. Exposure to
maximum rating conditions for extended periods may affect device reliability.
Table 5. Maximum Ratings
Rating
Symbol
Value
Unit
Maximum Acceleration (all axes, 100 μs)
gmax
5,000
g
Supply Voltage
VDD
-0.3 to + 3.6
V
Vin
-0.3 to VDDIO + 0.3
V
Drop Test
Ddrop
1.8
m
Operating Temperature Range
TOP
-40 to +85
°C
Storage Temperature Range
TSTG
-40 to +125
°C
Input voltage on any control pin (SA0, SCL, SDA)
Table 6. ESD and Latch-Up Protection Characteristics
Rating
Symbol
Value
Unit
Human Body Model
HBM
±2000
V
Machine Model
MM
±200
V
CDM
±500
V
—
±100
mA
Charge Device Model
Latch-up Current at T = 85°C
This device is sensitive to mechanical shock. Improper handling can cause permanent damage of the part or
cause the part to otherwise fail.
This is an ESD sensitive, improper handling can cause permanent damage to the part.
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3
Terminology
3.1
Sensitivity
The sensitivity is represented in counts/g. In 2g mode the sensitivity is 4096 counts/g. In 4g mode the sensitivity is 2048 counts/
g and in 8g mode the sensitivity is 1024 counts/g.
3.2
Zero-g Offset
Zero-g Offset (TyOff) describes the deviation of an actual output signal from the ideal output signal if the sensor is stationary. A
sensor stationary on a horizontal surface will measure 0g in X-axis and 0g in Y-axis whereas the Z-axis will measure 1g. The output
is ideally in the middle of the dynamic range of the sensor (content of OUT Registers 0x00, data expressed as 2's complement
number). A deviation from ideal value in this case is called Zero-g offset. Offset is to some extent a result of stress on the MEMS
sensor and therefore the offset can slightly change after mounting the sensor onto a printed circuit board or exposing it to
extensive mechanical stress.
3.3
Self-Test
Self-Test checks the transducer functionality without external mechanical stimulus. When Self-Test is activated, an electrostatic
actuation force is applied to the sensor, simulating a small acceleration. In this case the sensor outputs will exhibit a change in
their DC levels which are related to the selected full scale through the device sensitivity. When Self-Test is activated, the device
output level is given by the algebraic sum of the signals produced by the acceleration acting on the sensor and by the electrostatic
test-force.
4
Modes of Operation
SLEEP
ACTIVE
OFF
STANDBY
WAKE
Figure 6. MMA8451Q Mode Transition Diagram
Table 7. Mode of Operation Description
Mode
OFF
I2C Bus State
Powered Down
VDD
VDDIO
<1.8 V
VDDIO Can be > VDD
Function Description
The device is powered off. All analog and digital blocks
are shutdown. I2C bus inhibited.
STANDBY
I2C communication with
MMA8451Q is possible
ON
VDDIO = High
VDD = High
ACTIVE bit is cleared
Only digital blocks are enabled.
Analog subsystem is disabled. Internal clocks disabled.
ACTIVE
(WAKE/SLEEP)
I2C communication with
MMA8451Q is possible
ON
VDDIO = High
VDD = High
ACTIVE bit is set
All blocks are enabled (digital, analog).
All register contents are preserved when transitioning from ACTIVE to STANDBY mode. Some registers are reset when
transitioning from STANDBY to ACTIVE. These are all noted in the device memory map register table. The SLEEP and WAKE
modes are ACTIVE modes. For more information on how to use the SLEEP and WAKE modes and how to transition between
these modes please refer to the functionality section of this document.
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5
Functionality
The MMA8451Q is a low-power, digital output 3-axis linear accelerometer with a I2C interface and embedded logic used to
detect events and notify an external microprocessor over interrupt lines. The functionality includes the following:
• 8-bit or 14-bit data, High Pass Filtered data, 8-bit or 14-bit configurable 32 sample FIFO
• 4 different oversampling options for compromising between resolution and current consumption based on application
requirements
• Additional Low Noise mode that functions independently of the Oversampling modes for higher resolution
• Low Power and Auto-WAKE/SLEEP for conservation of current consumption
• Single/Double tap with directional information 1 channel
• Motion detection with directional information or Freefall 1 channel
• Transient/Jolt detection based on a high pass filter and settable threshold for detecting the change in acceleration above
a threshold with directional information 1 channel
• Flexible user configurable portrait landscape detection algorithm addressing many use cases for screen orientation
All functionality is available in 2g, 4g or 8g dynamic ranges. There are many configuration settings for enabling all the different
functions. Separate application notes have been provided to help configure the device for each embedded functionality.
5.1
Device Calibration
The device interface is factory calibrated for sensitivity and Zero-g offset for each axis. The trim values are stored in Non
Volatile Memory (NVM). On power-up, the trim parameters are read from NVM and applied to the circuitry. In normal use, further
calibration in the end application is not necessary. However, the MMA8451Q allows the user to adjust the Zero-g offset for each
axis after power-up, changing the default offset values. The user offset adjustments are stored in 6 volatile registers. For more
information on device calibration, refer to Freescale application note, AN4069.
5.2
8-bit or 14-bit Data
The measured acceleration data is stored in the OUT_X_MSB, OUT_X_LSB, OUT_Y_MSB, OUT_Y_LSB, OUT_Z_MSB, and
OUT_Z_LSB registers as 2’s complement 14-bit numbers. The most significant 8-bits of each axis are stored in OUT_X (Y,
Z)_MSB, so applications needing only 8-bit results can use these 3 registers and ignore OUT_X,Y, Z_LSB. To do this, the
F_READ bit in CTRL_REG1 must be set. When the F_READ bit is cleared, the fast read mode is disabled.
When the full-scale is set to 2g, the measurement range is -2g to +1.99975g, and each count corresponds to 1g/4096
(0.25 mg) at 14-bits resolution. When the full-scale is set to 8g, the measurement range is -8g to +7.999g, and each count
corresponds to 1g/1024 (0.98 mg) at 14-bits resolution. The resolution is reduced by a factor of 64 if only the 8-bit results are
used. For more information on the data manipulation between data formats and modes, refer to Freescale application note,
AN4076. There is a device driver available that can be used with the Sensor Toolbox demo board (LFSTBEB8451, 2, 3Q) with
this application note.
5.3
Internal FIFO Data Buffer
MMA8451Q contains a 32 sample internal FIFO data buffer minimizing traffic across the I2C bus. The FIFO can also provide
power savings of the system by allowing the host processor/MCU to go into a SLEEP mode while the accelerometer independently
stores the data, up to 32 samples per axis. The FIFO can run at all output data rates. There is the option of accessing the full
14-bit data or for accessing only the 8-bit data. When access speed is more important than high resolution the 8-bit data read is a
better option.
The FIFO contains four modes (Fill Buffer Mode, Circular Buffer Mode, Trigger Mode, and Disabled Mode) described in the
F_SETUP Register 0x09. Fill Buffer Mode collects the first 32 samples and asserts the overflow flag when the buffer is full and
another sample arrives. It does not collect any more data until the buffer is read. This benefits data logging applications where all
samples must be collected. The Circular Buffer Mode allows the buffer to be filled and then new data replaces the oldest sample in
the buffer. The most recent 32 samples will be stored in the buffer. This benefits situations where the processor is waiting for an
specific interrupt to signal that the data must be flushed to analyze the event. The trigger mode will hold the last data up to the
point when the trigger occurs and can be set to keep a selectable number of samples after the event occurs.
The MMA8451Q FIFO Buffer has a configurable watermark, allowing the processor to be triggered after a configurable number
of samples has filled in the buffer (1 to 32).
For details on the configurations for the FIFO buffer as well as more specific examples and application benefits, refer to
Freescale application note, AN4073.
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5.4
Low Power Modes vs. High Resolution Modes
The MMA8451Q can be optimized for lower power modes or for higher resolution of the output data. High resolution is
achieved by setting the LNOISE bit in Register 0x2A. This improves the resolution but be aware that the dynamic range is limited
to 4g when this bit is set. This will affect all internal functions and reduce noise. Another method for improving the resolution of
the data is by oversampling. One of the oversampling schemes of the data can activated when MODS = 10 in Register 0x2B
which will improve the resolution of the output data only. The highest resolution is achieved at 1.56 Hz.
There is a trade-off between low power and high resolution. Low Power can be achieved when the oversampling rate is
reduced. When MODS = 11 the lowest power is achieved. The lowest power is achieved when the sample rate is set to 1.56 Hz.
For more information on how to configure the MMA8451Q in Low Power mode or High Resolution mode and to realize the
benefits, refer to Freescale application note, AN4075.
5.5
Auto-WAKE/SLEEP Mode
The MMA8451Q can be configured to transition between sample rates (with their respective current consumption) based on
four of the interrupt functions of the device. The advantage of using the Auto-WAKE/SLEEP is that the system can automatically
transition to a higher sample rate (higher current consumption) when needed but spends the majority of the time in the SLEEP
mode (lower current) when the device does not require higher sampling rates. Auto-WAKE refers to the device being triggered by
one of the interrupt functions to transition to a higher sample rate. This may also interrupt the processor to transition from a SLEEP
mode to a higher power mode.
SLEEP mode occurs after the accelerometer has not detected an interrupt for longer than the user definable time-out period.
The device will transition to the specified lower sample rate. It may also alert the processor to go into a lower power mode to save
on current during this period of inactivity.
The Interrupts that can WAKE the device from SLEEP are the following: Tap Detection, Orientation Detection, Motion/Freefall,
and Transient Detection. The FIFO can be configured to hold the data in the buffer until it is flushed if the FIFO Gate bit is set in
Register 0x2C but the FIFO cannot WAKE the device from SLEEP.
The interrupts that can keep the device from falling asleep are the same interrupts that can wake the device with the addition
of the FIFO. If the FIFO interrupt is enabled and data is being accessed continually servicing the interrupt then the device will
remain in the WAKE mode. Refer to AN4074, for more detailed information for configuring the Auto-WAKE/SLEEP.
5.6
Freefall and Motion Detection
MMA8451Q has flexible interrupt architecture for detecting either a Freefall or a Motion. Freefall can be enabled where the set
threshold must be less than the configured threshold, or motion can be enabled where the set threshold must be greater than
the threshold. The motion configuration has the option of enabling or disabling a high pass filter to eliminate tilt data (static offset).
The freefall does not use the high pass filter. For details on the Freefall and Motion detection with specific application examples
and recommended configuration settings, refer to Freescale application note AN4070.
5.6.1
Freefall Detection
The detection of “Freefall” involves the monitoring of the X, Y, and Z axes for the condition where the acceleration magnitude
is below a user specified threshold for a user definable amount of time. Normally the usable threshold ranges are between
±100 mg and ±500 mg.
5.6.2
Motion Detection
Motion is often used to simply alert the main processor that the device is currently in use. When the acceleration exceeds a
set threshold the motion interrupt is asserted. A motion can be a fast moving shake or a slow moving tilt. This will depend on the
threshold and timing values configured for the event. The motion detection function can analyze static acceleration changes or
faster jolts. For example, to detect that an object is spinning, all three axes would be enabled with a threshold detection of > 2g.
This condition would need to occur for a minimum of 100 ms to ensure that the event wasn't just noise. The timing value is set
by a configurable debounce counter. The debounce counter acts like a filter to determine whether the condition exists for
configurable set of time (i.e., 100 ms or longer). There is also directional data available in the source register to detect the
direction of the motion. This is useful for applications such as directional shake or flick, which assists with the algorithm for various
gesture detections.
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5.7
Transient Detection
The MMA8451Q has a built-in high pass filter. Acceleration data goes through the high pass filter, eliminating the offset (DC)
and low frequencies. The high pass filter cut-off frequency can be set by the user to four different frequencies which are
dependent on the Output Data Rate (ODR). A higher cut-off frequency ensures the DC data or slower moving data will be filtered
out, allowing only the higher frequencies to pass. The embedded Transient Detection function uses the high pass filtered data
allowing the user to set the threshold and debounce counter. The transient detection feature can be used in the same manner as
the motion detection by bypassing the high pass filter. There is an option in the configuration register to do this. This adds more
flexibility to cover various customer use cases.
Many applications use the accelerometer’s static acceleration readings (i.e., tilt) which measure the change in acceleration
due to gravity only. These functions benefit from acceleration data being filtered with a low pass filter where high frequency data is
considered noise. However, there are many functions where the accelerometer must analyze dynamic acceleration. Functions
such as tap, flick, shake and step counting are based on the analysis of the change in the acceleration. It is simpler to interpret
these functions dependent on dynamic acceleration data when the static component has been removed. The Transient Detection
function can be routed to either interrupt pin through bit 5 in CTRL_REG5 register (0x2E). Registers 0x1D – 0x20 are the
dedicated Transient Detection configuration registers. The source register contains directional data to determine the direction of
the acceleration, either positive or negative. For details on the benefits of the embedded Transient Detection function along with
specific application examples and recommended configuration settings, please refer to Freescale application note, AN4071.
5.8
Tap Detection
The MMA8451Q has embedded single/double and directional tap detection. This function has various customizing timers for
setting the pulse time width and the latency time between pulses. There are programmable thresholds for all three axes. The tap
detection can be configured to run through the high pass filter and also through a low pass filter, which provides more customizing
and tunable tap detection schemes. The status register provides updates on the axes where the event was detected and the
direction of the tap. For more information on how to configure the device for tap detection please refer to Freescale application
note AN4072.
5.9
Orientation Detection
The MMA8451Q incorporates an advanced algorithm for orientation detection (ability to detect all 6 orientations) with
configurable trip points. The embedded algorithm allows the selection of the mid point with the desired hysteresis value.
The MMA8451Q Orientation Detection algorithm confirms the reliability of the function with a configurable Z-lockout angle.
Based on known functionality of linear accelerometers, it is not possible to rotate the device about the Z-axis to detect change in
acceleration at slow angular speeds. The angle at which the device no longer detects the orientation change is referred to as the
“Z-Lockout angle”. The device operates down to 14° from the flat position.
For further information on the configuration settings of the orientation detection function, including recommendations for
configuring the device to support various application use cases, refer to Freescale application note, AN4068.
Figure 8 and Figure 9 show the definitions of the trip angles going from Landscape to Portrait and then also from Portrait to
Landscape.
Top View
Pin 1
PU
Earth Gravity
Side View
BACK
LL
LR
Xout @ 0g
Yout @ -1g
Zout @ 0g
Xout @ 0g
Yout @ 0g
Zout @ -1g
FRONT
PD
Xout @ -1g
Yout @ 0g
Zout @ 0g
Xout @ 1g
Yout @ 0g
Zout @ 0g
Xout @ 0g
Yout @ 0g
Zout @ 1g
Xout @ 0g
Yout @ 1g
Zout @ 0g
Figure 7. Landscape/Portrait Orientation
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PORTRAIT
90°
PORTRAIT
90°
Landscape to Portrait
Trip Angle = 60°
Portrait to Landscape
Trip Angle = 30°
0° Landscape
Figure 8. Illustration of Landscape to Portrait Transition
0° Landscape
Figure 9. Illustration of Portrait to Landscape Transition
Figure 10 illustrates the Z-angle lockout region. When lifting the device upright from the flat position it will be active for
orientation detection as low as14° from flat. This is user configurable. The default angle is 29° but it can be set as low as 14°.
.
UPRIGHT
90°
NORMAL
DETECTION
REGION
Z-LOCK = 29°
LOCKOUT
REGION
0° FLAT
Figure 10. Illustration of Z-Tilt Angle Lockout Transition
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5.10
Interrupt Register Configurations
There are seven configurable interrupts in the MMA8451Q: Data Ready, Motion/Freefall, Tap (Pulse), Orientation, Transient,
FIFO and Auto-SLEEP events. These seven interrupt sources can be routed to one of two interrupt pins. The interrupt source
must be enabled and configured. If the event flag is asserted because the event condition is detected, the corresponding interrupt
pin, INT1 or INT2, will assert.
Data Ready
Motion/Freefall
INT1
Tap (Pulse)
Orientation
INTERRUPT
CONTROLLER
Transient
INT2
FIFO
Auto-SLEEP
7
INT ENABLE
7
INT CFG
Figure 11. System Interrupt Generation Block Diagram
5.11
Serial
I2C
Interface
Acceleration data may be accessed through an I2C interface thus making the device particularly suitable for direct interfacing
with a microcontroller. The MMA8451Q features an interrupt signal which indicates when a new set of measured acceleration
data is available thus simplifying data synchronization in the digital system that uses the device. The MMA8451Q may also be
configured to generate other interrupt signals accordingly to the programmable embedded functions of the device for Motion,
Freefall, Transient, Orientation, and Tap.
The registers embedded inside the MMA8451Q are accessed through the I2C serial interface (Table 8). To enable the I2C
interface, VDDIO line must be tied high (i.e., to the interface supply voltage). If VDD is not present and VDDIO is present, the
MMA8451Q is in off mode and communications on the I2C interface are ignored. The I2C interface may be used for
communications between other I2C devices and the MMA8451Q does not affect the I2C bus.
Table 8. Serial Interface Pin Description
Pin Name
Pin Description
SCL
I2C
SDA
2
I C Serial Data
SA0
I2C least significant bit of the device address
Serial Clock
There are two signals associated with the I2C bus; the Serial Clock Line (SCL) and the Serial Data line (SDA). The latter is a
bidirectional line used for sending and receiving the data to/from the interface. External pull-up resistors connected to VDDIO are
expected for SDA and SCL. When the bus is free both the lines are high. The I2C interface is compliant with Fast mode (400 kHz),
and Normal mode (100 kHz) I2C standards (Table 4).
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5.11.1
I2C Operation
The transaction on the bus is started through a start condition (START) signal. START condition is defined as a HIGH to LOW
transition on the data line while the SCL line is held HIGH. After START has been transmitted by the Master, the bus is considered
busy. The next byte of data transmitted after START contains the slave address in the first 7 bits, and the eighth bit tells whether
the Master is receiving data from the slave or transmitting data to the slave. When an address is sent, each device in the system
compares the first seven bits after a start condition with its address. If they match, the device considers itself addressed by the
Master. The 9th clock pulse, following the slave address byte (and each subsequent byte) is the acknowledge (ACK). The
transmitter must release the SDA line during the ACK period. The receiver must then pull the data line low so that it remains
stable low during the high period of the acknowledge clock period.
A LOW to HIGH transition on the SDA line while the SCL line is high is defined as a stop condition (STOP). A data transfer is
always terminated by a STOP. A Master may also issue a repeated START during a data transfer. The MMA8451Q expects
repeated STARTs to be used to randomly read from specific registers.
The MMA8451Q's standard slave address is a choice between the two sequential addresses 0011100 and 0011101. The
selection is made by the high and low logic level of the SA0 (pin 7) input respectively. The slave addresses are factory
programmed and alternate addresses are available at customer request. The format is shown in Table 9.
Table 9. I2C Address Selection Table
Slave Address (SA0 = 0)
Slave Address (SA0 = 1)
Comment
0011100 (0x1C)
0011101 (0x1D)
Factory Default
Single Byte Read
The MMA8451Q has an internal ADC that can sample, convert and return sensor data on request. The transmission of an
8-bit command begins on the falling edge of SCL. After the eight clock cycles are used to send the command, note that the data
returned is sent with the MSB first once the data is received. Figure 12 shows the timing diagram for the accelerometer 8-bit I2C
read operation. The Master (or MCU) transmits a start condition (ST) to the MMA8451Q, slave address ($1D), with the R/W bit
set to “0” for a write, and the MMA8451Q sends an acknowledgement. Then the Master (or MCU) transmits the address of the
register to read and the MMA8451Q sends an acknowledgement. The Master (or MCU) transmits a repeated start condition (SR)
and then addresses the MMA8451Q ($1D) with the R/W bit set to “1” for a read from the previously selected register. The Slave
then acknowledges and transmits the data from the requested register. The Master does not acknowledge (NAK) the transmitted
data, but transmits a stop condition to end the data transfer.
Multiple Byte Read
When performing a multi-byte read or “burst read”, the MMA8451Q automatically increments the received register address
commands after a read command is received. Therefore, after following the steps of a single byte read, multiple bytes of data
can be read from sequential registers after each MMA8451Q acknowledgment (AK) is received until a no acknowledge (NAK)
occurs from the Master followed by a stop condition (SP) signaling an end of transmission.
Single Byte Write
To start a write command, the Master transmits a start condition (ST) to the MMA8451Q, slave address ($1D) with the R/W bit
set to “0” for a write, the MMA8451Q sends an acknowledgement. Then the Master (MCU) transmits the address of the register
to write to, and the MMA8451Q sends an acknowledgement. Then the Master (or MCU) transmits the 8-bit data to write to the
designated register and the MMA8451Q sends an acknowledgement that it has received the data. Since this transmission is
complete, the Master transmits a stop condition (SP) to the data transfer. The data sent to the MMA8451Q is now stored in the
appropriate register.
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Multiple Byte Write
The MMA8451Q automatically increments the received register address commands after a write command is received.
Therefore, after following the steps of a single byte write, multiple bytes of data can be written to sequential registers after each
MMA8451Q acknowledgment (ACK) is received.
Table 10. I2C Device Address Sequence
[6:1]
Device Address
Command
[0]
SA0
[6:0]
Device Address
R/W
8-bit Final Value
Read
001110
0
0x1C
1
0x39
Write
001110
0
0x1C
0
0x38
Read
001110
1
0x1D
1
0x3B
Write
001110
1
0x1D
0
0x3A
< Single Byte Read >
Master
ST
Device Address[6:0]
W
Register Address[7:0]
AK
Slave
SR
Device Address[6:0]
R
AK
NAK SP
AK
Data[7:0]
< Multiple Byte Read >
Master
ST
Device Address[6:0]
W
Register Address[7:0]
AK
Slave
AK
Data[7:0]
Slave
R
AK
AK
Master
SR Device Address[6:0]
Data[7:0]
AK
AK
NAK
Data[7:0]
SP
Data[7:0]
< Single Byte Write >
ST
Master
Device Address[6:0]
W
Register Address[7:0]
AK
Slave
Data[7:0]
AK
SP
AK
< Multiple Byte Write >
Master
ST
Device Address[6:0]
Slave
W
Register Address[7:0]
AK
Data[7:0]
AK
Data[7:0]
AK
SP
AK
Legend
ST: Start Condition
SP: Stop Condition
NAK: No Acknowledge
SR: Repeated Start Condition
AK: Acknowledge
R: Read = 1
W: Write = 0
Figure 12. I2C Timing Diagram
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Register Descriptions
Table 11. Register Address Map
Name
Type
Auto-Increment Address
Register
Address FMODE = 0 FMODE > 0 FMODE = 0 FMODE > 0
Default
Hex
Value
Comment
00000000
0x00
FMODE = 0, real time status
FMODE > 0, FIFO status
Output
—
[7:0] are 8 MSBs Root pointer to
of 14-bit sample. XYZ FIFO data.
Output
—
[7:2] are 6 LSBs of 14-bit real-time
sample
Output
—
[7:0] are 8 MSBs of 14-bit real-time
sample
F_READ = 0 F_READ = 0 F_READ = 1 F_READ = 1
STATUS/F_STATUS(1)(2)
R
0x00
OUT_X_MSB(1)(2)
R
0x01
OUT_X_LSB(1)(2)
R
0x02
0x03
OUT_Y_MSB(1)(2)
R
0x03
0x04
OUT_Y_LSB(1)(2)
R
0x04
0x05
0x00
Output
—
[7:2] are 6 LSBs of 14-bit real-time
sample
OUT_Z_MSB(1)(2)
R
0x05
0x06
0x00
Output
—
[7:0] are 8 MSBs of 14-bit real-time
sample
OUT_Z_LSB(1)(2)
R
0x06
Output
—
[7:2] are 6 LSBs of 14-bit real-time
sample
Reserved
R
0x07
—
—
—
—
—
—
Reserved. Read return 0x00.
Reserved
R
0x08
—
—
—
—
—
—
Reserved. Read return 0x00.
R/W
0x09
00000000
0x00
FIFO set-up
(1)(3)
F_SETUP
TRIG_CFG
(1)(4)
0x01
0x02
0x01
0x03
0x01
0x00
0x05
0x00
0x00
0x0A
R/W
0x0A
0x0B
00000000
0x00
Map of FIFO data capture events
R
0x0B
0x0C
00000000
0x00
Current System Mode
(1)(2)
R
0x0C
0x0D
00000000
0x00
Interrupt status
(1)
R
0x0D
0x0E
00011010
0x1A
Device ID (0x1A)
R/W
0x0E
0x0F
00000000
0x00
Dynamic Range Settings
SYSMOD(1)(2)
INT_SOURCE
WHO_AM_I
XYZ_DATA_CFG
(1)(4)
HP_FILTER_CUTOFF(1)(4)
R/W
0x0F
0x10
00000000
0x00
Cut-off frequency is set to 16 Hz @
800 Hz
PL_STATUS(1)(2)
R
0x10
0x11
00000000
0x00
Landscape/Portrait orientation
status
PL_CFG(1)(4)
R/W
0x11
0x12
10000000
0x80
Landscape/Portrait configuration.
PL_COUNT(1)(3)
R/W
0x12
0x13
00000000
0x00
Landscape/Portrait debounce
counter
PL_BF_ZCOMP(1)(4)
R/W
0x13
0x14
01000100
0x44
Back/Front, Z-Lock Trip threshold
P_L_THS_REG(1)(4)
R/W
0x14
0x15
10000100
0x84
Portrait to Landscape Trip Angle is
29°
FF_MT_CFG(1)(4)
R/W
0x15
0x16
00000000
0x00
Freefall/Motion functional block
configuration
FF_MT_SRC(1)(2)
R
0x16
0x17
00000000
0x00
Freefall/Motion event source
register
FF_MT_THS(1)(3)
R/W
0x17
0x18
00000000
0x00
Freefall/Motion threshold register
R/W
0x18
0x19
00000000
0x00
Freefall/Motion debounce counter
Reserved
R
0x19
—
—
—
—
—
—
Reserved. Read return 0x00.
Reserved
R
0x1A
—
—
—
—
—
—
Reserved. Read return 0x00.
Reserved
R
0x1B
—
—
—
—
—
—
Reserved. Read return 0x00.
Reserved
R
0x1C
—
—
—
—
—
—
Reserved. Read return 0x00.
TRANSIENT_CFG(1)(4)
R/W
0x1D
0x1E
00000000
0x00
Transient functional block
configuration
TRANSIENT_SRC(1)(2)
R
0x1E
0x1F
00000000
0x00
Transient event status register
FF_MT_COUNT
(1)(3)
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Table 11. Register Address Map
TRANSIENT_THS(1)(3)
(1)(3)
R/W
0x1F
0x20
00000000
0x00
Transient event threshold
R/W
0x20
0x21
00000000
0x00
Transient debounce counter
PULSE_CFG(1)(4)
R/W
0x21
0x22
00000000
0x00
ELE, Double_XYZ or Single_XYZ
PULSE_SRC(1)(2)
TRANSIENT_COUNT
R
0x22
0x23
00000000
0x00
EA, Double_XYZ or Single_XYZ
(1)(3)
R/W
0x23
0x24
00000000
0x00
X pulse threshold
(1)(3)
PULSE_THSY
R/W
0x24
0x25
00000000
0x00
Y pulse threshold
PULSE_THSZ(1)(3)
R/W
0x25
0x26
00000000
0x00
Z pulse threshold
(1)(4)
R/W
0x26
0x27
00000000
0x00
Time limit for pulse
(1)(4)
R/W
0x27
0x28
00000000
0x00
Latency time for 2nd pulse
PULSE_WIND(1)(4)
R/W
0x28
0x29
00000000
0x00
Window time for 2nd pulse
ASLP_COUNT(1)(4)
R/W
0x29
0x2A
00000000
0x00
Counter setting for Auto-SLEEP
CTRL_REG1(1)(4)
R/W
0x2A
0x2B
00000000
0x00
ODR = 800 Hz, STANDBY Mode.
CTRL_REG2(1)(4)
R/W
0x2B
0x2C
00000000
0x00
Sleep Enable, OS Modes,
RST, ST
CTRL_REG3(1)(4)
R/W
0x2C
0x2D
00000000
0x00
Wake from Sleep, IPOL, PP_OD
CTRL_REG4
(1)(4)
R/W
0x2D
0x2E
00000000
0x00
Interrupt enable register
CTRL_REG5
(1)(4)
PULSE_THSX
PULSE_TMLT
PULSE_LTCY
R/W
0x2E
0x2F
00000000
0x00
Interrupt pin (INT1/INT2) map
OFF_X(1)(4)
R/W
0x2F
0x30
00000000
0x00
X-axis offset adjust
(1)(4)
R/W
0x30
0x31
00000000
0x00
Y-axis offset adjust
(1)(4)
R/W
0x31
0x0D
00000000
0x00
Z-axis offset adjust
0x40 – 7F
—
—
—
Reserved. Read return 0x00.
OFF_Y
OFF_Z
Reserved (do not modify)
1. Register contents are preserved when transition from ACTIVE to STANDBY mode occurs.
2. Register contents are reset when transition from STANDBY to ACTIVE mode occurs.
3. Register contents can be modified anytime in STANDBY or ACTIVE mode. A write to this register will cause a reset of the corresponding
internal system debounce counter.
4. Modification of this register’s contents can only occur when device is STANDBY mode except CTRL_REG1 ACTIVE bit and CTRL_REG2 RST
bit.
Note: Auto-increment addresses which are not a simple increment are highlighted in bold. The auto-increment addressing is only enabled when
device registers are read using I2C burst read mode. Therefore the internal storage of the auto-increment address is cleared whenever a
stop-bit is detected.
6.1
Data Registers
The following are the data registers for the MMA8451Q. For more information on data manipulation of the MMA8451Q, refer
to application note, AN4076.
When the F_MODE bits found in Register 0x09 (F_SETUP), bits 7 and 6 are both cleared (the FIFO is not on). Register 0x00
reflects the real-time status information of the X, Y and Z sample data. When the F_MODE value is greater than zero the FIFO
is on (in either Fill, Circular or Trigger mode). In this case Register 0x00 will reflect the status of the FIFO. It is expected when the
FIFO is on that the user will access the data from Register 0x01 (X_MSB) for either the 14-bit or 8-bit data. When accessing the
8-bit data the F_READ bit (Register 0x2A) is set which modifies the auto-incrementing to skip over the LSB data. When F_READ
bit is cleared the 14-bit data is read accessing all 6 bytes sequentially (X_MSB, X_LSB, Y_MSB, Y_LSB, Z_MSB, Z_LSB).
F_MODE = 00: 0x00 STATUS: Data Status Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
ZYXOW
ZOW
YOW
XOW
ZYXDR
ZDR
YDR
XDR
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Table 12. STATUS Description
ZYXOW
X, Y, Z-axis Data Overwrite. Default value: 0
0: No data overwrite has occurred
1: Previous X, Y, or Z data was overwritten by new X, Y, or Z data before it was read
ZOW
Z-axis Data Overwrite. Default value: 0
0: No data overwrite has occurred
1: Previous Z-axis data was overwritten by new Z-axis data before it was read
YOW
Y-axis Data Overwrite. Default value: 0
0: No data overwrite has occurred
1: Previous Y-axis data was overwritten by new Y-axis data before it was read
XOW
X-axis Data Overwrite. Default value: 0
0: No data overwrite has occurred
1: Previous X-axis data was overwritten by new X-axis data before it was read
ZYXDR
X, Y, Z-axis new Data Ready. Default value: 0
0: No new set of data ready
1: A new set of data is ready
ZDR
Z-axis new Data Available. Default value: 0
0: No new Z-axis data is ready
1: A new Z-axis data is ready
YDR
Y-axis new Data Available. Default value: 0
0: No new Y-axis data ready
1: A new Y-axis data is ready
XDR
X-axis new Data Available. Default value: 0
0: No new X-axis data ready
1: A new X-axis data is ready
ZYXOW is set whenever a new acceleration data is produced before completing the retrieval of the previous set. This event
occurs when the content of at least one acceleration data register (i.e., OUT_X, OUT_Y, OUT_Z) has been overwritten. ZYXOW
is cleared when the high-bytes of the acceleration data (OUT_X_MSB, OUT_Y_MSB, OUT_Z_MSB) of all the active channels are
read.
ZOW is set whenever a new acceleration sample related to the Z-axis is generated before the retrieval of the previous sample.
When this occurs the previous sample is overwritten. ZOW is cleared anytime OUT_Z_MSB register is read.
YOW is set whenever a new acceleration sample related to the Y-axis is generated before the retrieval of the previous sample.
When this occurs the previous sample is overwritten. YOW is cleared anytime OUT_Y_MSB register is read.
XOW is set whenever a new acceleration sample related to the X-axis is generated before the retrieval of the previous sample.
When this occurs the previous sample is overwritten. XOW is cleared anytime OUT_X_MSB register is read.
ZYXDR signals that a new sample for any of the enabled channels is available. ZYXDR is cleared when the high-bytes of the
acceleration data (OUT_X_MSB, OUT_Y_MSB, OUT_Z_MSB) of all the enabled channels are read.
ZDR is set whenever a new acceleration sample related to the Z-axis is generated. ZDR is cleared anytime OUT_Z_MSB register
is read.
YDR is set whenever a new acceleration sample related to the Y-axis is generated. YDR is cleared anytime OUT_Y_MSB register
is read.
XDR is set whenever a new acceleration sample related to the X-axis is generated. XDR is cleared anytime OUT_X_MSB register
is read.
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Data Registers: 0x01 OUT_X_MSB, 0x02 OUT_X_LSB, 0x03 OUT_Y_MSB, 0x04 OUT_Y_LSB, 0x05 OUT_Z_MSB, 0x06
OUT_Z_LSB
These registers contain the X-axis, Y-axis, and Z-axis14-bit output sample data expressed as 2's complement numbers.
Note: The sample data output registers store the current sample data if the FIFO data output register driver is disabled, but if
the FIFO data output register driver is enabled (F_MODE > 00) the sample data output registers point to the head of the FIFO
buffer (Register 0x01 X_MSB) which contains the previous 32 X, Y, and Z data samples. Data Registers F_MODE = 00
0x01 OUT_X_MSB: X_MSB Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
XD13
XD12
XD11
XD10
XD9
XD8
XD7
XD6
0x02 OUT_X_LSB: X_LSB Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
XD5
XD4
XD3
XD2
XD1
XD0
0
0
0x03 OUT_Y_MSB: Y_MSB Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
YD13
YD12
YD11
YD10
YD9
YD8
YD7
YD6
0x04 OUT_Y_LSB: Y_LSB Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
YD5
YD4
YD3
YD2
YD1
YD0
0
0
0x05 OUT_Z_MSB: Z_MSB Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
ZD13
ZD12
ZD11
ZD10
ZD9
ZD8
ZD7
ZD6
0x06 OUT_Z_LSB: Z_LSB Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
ZD5
ZD4
ZD3
ZD2
ZD1
ZD0
0
0
OUT_X_MSB, OUT_X_LSB, OUT_Y_MSB, OUT_Y_LSB, OUT_Z_MSB, and OUT_Z_LSB are stored in the autoincrementing address range of 0x01 to 0x06 to reduce reading the status followed by 14-bit axis data to 7 bytes. If the F_READ
bit is set (0x2A bit 1), auto increment will skip over LSB registers. This will shorten the data acquisition from
7 bytes to 4 bytes. The LSB registers can only be read immediately following the read access of the corresponding MSB register.
A random read access to the LSB registers is not possible. Reading the MSB register and then the LSB register in sequence
ensures that both bytes (LSB and MSB) belong to the same data sample, even if a new data sample arrives between reading the
MSB and the LSB byte.
If the FIFO is enabled (F_MODE > 00), Register 0x01 points to the FIFO read pointer, while registers 0x02, 0x03, 0x04, 0x05,
0x06 return a value of zero when read. If the F_READ bit is set (0x2A bit 1), auto increment will skip over LSB registers to access
the MSB data only.
6.2
32 Sample FIFO
The following registers are used to configure the FIFO. For more information on the FIFO please refer to AN4073.
F_MODE > 0 0x00: F_STATUS FIFO Status Register
When F_MODE > 0, Register 0x00 becomes the FIFO Status Register which is used to retrieve information about the FIFO.
This register has a flag for the overflow and watermark. It also has a counter that can be read to obtain the number of samples
stored in the buffer when the FIFO is enabled.
0x00 F_STATUS: FIFO STATUS Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
F_OVF
F_WMRK_FLAG
F_CNT5
F_CNT4
F_CNT3
F_CNT2
F_CNT1
F_CNT0
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Table 13. FIFO Flag Event Description
F_OVF
F_WMRK_FLAG
Event Description
0
—
No FIFO overflow events detected.
1
—
FIFO event detected; FIFO has overflowed.
—
0
No FIFO watermark events detected.
—
1
FIFO Watermark event detected. FIFO sample count is greater than watermark value.
If F_MODE = 11, Trigger Event detected.
The F_OVF and F_WMRK_FLAG flags remain asserted while the event source is still active, but the user can clear the FIFO
interrupt bit flag in the interrupt source register (INT_SOURCE) by reading the F_STATUS register. In this case, the SRC_FIFO
bit in the INT_SOURCE register will be set again when the next data sample enters the FIFO. Therefore the F_OVF bit flag will
remain asserted while the FIFO has overflowed and the F_WMRK_FLAG bit flag will remain asserted while the F_CNT value is
equal to or greater than then F_WMRK value. If the FIFO overflow flag is cleared and if F_MODE = 11 then the FIFO overflow
flag will remain 0 before the trigger event even if the FIFO is full and overflows. If the FIFO overflow flag is set and if F_MODE
is = 11, the FIFO has stopped accepting samples.
Table 14. FIFO Sample Count Description
FIFO sample counter. Default value: 00_0000.
(00_0001 to 10_0000 indicates 1 to 32 samples stored in FIFO
F_CNT[5:0]
F_CNT[5:0] bits indicate the number of acceleration samples currently stored in the FIFO buffer. Count 000000 indicates that the
FIFO is empty.
0x09: F_SETUP FIFO Set-up Register
0x09 F_SETUP: FIFO Set-up Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
F_MODE1
F_MODE0
F_WMRK5
F_WMRK4
F_WMRK3
F_WMRK2
F_WMRK1
F_WMRK0
Table 15. F_SETUP Description
BITS
F_MODE[1:0](1)(2)
F_WMRK[5:0](2)
Description
FIFO buffer overflow mode. Default value: 0.
00: FIFO is disabled.
01: FIFO contains the most recent samples when overflowed (circular buffer). Oldest sample is discarded to
be replaced by new sample.
10: FIFO stops accepting new samples when overflowed.
11: Trigger mode. The FIFO will be in a circular mode up to the number of samples in the watermark. The
FIFO will be in a circular mode until the trigger event occurs after that the FIFO will continue to accept samples
for 32-WMRK samples and then stop receiving further samples. This allows data to be collected both before
and after the trigger event and it is definable by the watermark setting.
The FIFO is flushed whenever the FIFO is disabled, during an automatic ODR change (Auto-WAKE/SLEEP),
or transitioning from STANDBY mode to ACTIVE mode.
Disabling the FIFO (F_MODE = 00) resets the F_OVF, F_WMRK_FLAG, F_CNT to zero.
A FIFO overflow event (i.e., F_CNT = 32) will assert the F_OVF flag and a FIFO sample count equal to the
sample count watermark (i.e., F_WMRK) asserts the F_WMRK_FLAG event flag.
FIFO Event Sample Count Watermark. Default value: 00_0000.
These bits set the number of FIFO samples required to trigger a watermark interrupt. A FIFO watermark event
flag is raised when FIFO sample count F_CNT[5:0] ≥ F_WMRK[5:0] watermark.
Setting the F_WMRK[5:0] to 00_0000 will disable the FIFO watermark event flag generation.
Also used to set the number of pre-trigger samples in Trigger mode.
1. Bit field can be written in ACTIVE mode.
2. Bit field can be written in STANDBY mode.
The FIFO mode can be changed while in the active state. The mode must first be disabled F_MODE = 00 then the mode can
be switched between Fill mode, Circular mode and Trigger mode.
A FIFO sample count exceeding the watermark event does not stop the FIFO from accepting new data. The FIFO update rate
is dictated by the selected system ODR. In ACTIVE mode the ODR is set by the DR bits in the CTRL_REG1 register. When AutoSLEEP is active the ODR is set by the ASLP_RATE field in the CTRL_REG1 register.
When a byte is read from the FIFO buffer the oldest sample data in the FIFO buffer is returned and also deleted from the front
of the FIFO buffer, while the FIFO sample count is decremented by one. It is assumed that the host application shall use the I2C
multi-byte read transaction to empty the FIFO.
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0x0A: TRIG_CFG
In the trigger configuration register the bits that are set (logic ‘1’) control which function may trigger the FIFO to its interrupt
and conversely bits that are cleared (logic ‘0’) indicate which function has not asserted its interrupt.
The bits set are rising edge sensitive, and are set by a low to high state change and reset by reading the appropriate source
register.
0x0A: TRIG_CFG Trigger Configuration Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
—
—
Trig_TRANS
Trig_LNDPRT
Trig_PULSE
Trig_FF_MT
—
—
Table 16. Trigger Configuration Description
INT_SOURCE
Trig_TRANS
Trig_LNDPRT
Description
Transient interrupt trigger bit. Default value: 0
Landscape/Portrait Orientation interrupt trigger bit. Default value: 0
Trig_PULSE
Pulse interrupt trigger bit. Default value: 0
Trig_FF_MT
Freefall/Motion trigger bit. Default value: 0
0x0B: SYSMOD System Mode Register
The System mode register indicates the current device operating mode. Applications using the Auto-SLEEP/WAKE
mechanism should use this register to synchronize the application with the device operating mode transitions. The System mode
register also indicates the status of the FIFO gate error and number of samples since the gate error occurred.
0x0B SYSMOD: System Mode Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
FGERR
FGT_4
FGT_3
FGT_2
FGT_1
FGT_0
SYSMOD1
SYSMOD0
Table 17. SYSMOD Description
FIFO Gate Error. Default value: 0.
FGERR
0: No FIFO Gate Error detected.
1: FIFO Gate Error was detected.
Emptying the FIFO buffer clears the FGERR bit in the SYS_MOD register.
See section 0x2C: CTRL_REG3 Interrupt Control Register for more information on configuring the FIFO Gate function.
FGT[4:0]
Number of ODR time units since FGERR was asserted. Reset when FGERR Cleared. Default value: 0_0000
System Mode. Default value: 00.
SYSMOD[1:0]
00: STANDBY mode
01: WAKE mode
10: SLEEP mode
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0x0C: INT_SOURCE System Interrupt Status Register
In the interrupt source register the status of the various embedded features can be determined. The bits that are set (logic ‘1’)
indicate which function has asserted an interrupt and conversely the bits that are cleared (logic ‘0’) indicate which function has
not asserted or has de-asserted an interrupt. The bits are set by a low to high transition and are cleared by reading the
appropriate interrupt source register. The SRC_DRDY bit is cleared by reading the X, Y and Z data. It is not cleared by simply
reading the Status Register (0x00).
0x0C INT_SOURCE: System Interrupt Status Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
SRC_ASLP
SRC_FIFO
SRC_TRANS
SRC_LNDPRT
SRC_PULSE
SRC_FF_MT
—
SRC_DRDY
Table 18. INT_SOURCE Description
INT_SOURCE
Description
SRC_ASLP
Auto-SLEEP/WAKE interrupt status bit. Default value: 0.
Logic ‘1’ indicates that an interrupt event that can cause a WAKE to SLEEP or SLEEP to WAKE system mode transition
has occurred.
Logic ‘0’ indicates that no WAKE to SLEEP or SLEEP to WAKE system mode transition interrupt event has occurred.
WAKE to SLEEP transition occurs when no interrupt occurs for a time period that exceeds the user specified limit
(ASLP_COUNT). This causes the system to transition to a user specified low ODR setting.
SLEEP to WAKE transition occurs when the user specified interrupt event has woken the system; thus causing the
system to transition to a user specified high ODR setting.
Reading the SYSMOD register clears the SRC_ASLP bit.
SRC_FIFO
FIFO interrupt status bit. Default value: 0.
Logic ‘1’ indicates that a FIFO interrupt event such as an overflow event or watermark has occurred. Logic ‘0’ indicates
that no FIFO interrupt event has occurred.
FIFO interrupt event generators: FIFO Overflow, or (Watermark: F_CNT = F_WMRK) and the interrupt has been
enabled.
This bit is cleared by reading the F_STATUS register.
SRC_TRANS
Transient interrupt status bit. Default value: 0.
Logic ‘1’ indicates that an acceleration transient value greater than user specified threshold has occurred. Logic ‘0’
indicates that no transient event has occurred.
This bit is asserted whenever “EA” bit in the TRANS_SRC is asserted and the interrupt has been enabled. This bit is
cleared by reading the TRANS_SRC register.
SRC_LNDPRT
Landscape/Portrait Orientation interrupt status bit. Default value: 0.
Logic ‘1’ indicates that an interrupt was generated due to a change in the device orientation status. Logic ‘0’ indicates
that no change in orientation status was detected.
This bit is asserted whenever “NEWLP” bit in the PL_STATUS is asserted and the interrupt has been enabled.
This bit is cleared by reading the PL_STATUS register.
SRC_PULSE
Pulse interrupt status bit. Default value: 0.
Logic ‘1’ indicates that an interrupt was generated due to single and/or double pulse event. Logic ‘0’ indicates that no
pulse event was detected.
This bit is asserted whenever “EA” bit in the PULSE_SRC is asserted and the interrupt has been enabled.
This bit is cleared by reading the PULSE_SRC register.
SRC_FF_MT
Freefall/Motion interrupt status bit. Default value: 0.
Logic ‘1’ indicates that the Freefall/Motion function interrupt is active. Logic ‘0’ indicates that no Freefall or Motion event
was detected.
This bit is asserted whenever “EA” bit in the FF_MT_SRC register is asserted and the FF_MT interrupt has been
enabled.
This bit is cleared by reading the FF_MT_SRC register.
SRC_DRDY
Data Ready Interrupt bit status. Default value: 0.
Logic ‘1’ indicates that the X, Y, Z data ready interrupt is active indicating the presence of new data and/or data overrun.
Otherwise if it is a logic ‘0’ the X, Y, Z interrupt is not active.
This bit is asserted when the ZYXOW and/or ZYXDR is set and the interrupt has been enabled.
This bit is cleared by reading the X, Y, and Z data.
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0x0D: WHO_AM_I Device ID Register
The device identification register identifies the part. The default value is 0x1A. This value is factory programmed. Consult the
factory for custom alternate values.
0x0D: WHO_AM_I Device ID Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
1
1
0
1
0
0x0E: XYZ_DATA_CFG Register
The XYZ_DATA_CFG register sets the dynamic range and sets the high pass filter for the output data. When the HPF_OUT
bit is set, both the FIFO and DATA registers will contain high pass filtered data.
0x0E: XYZ_DATA_CFG (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
HPF_OUT
0
0
FS1
FS0
Table 19. XYZ Data Configuration Descriptions
HPF_OUT
FS[1:0]
Enable High pass output data 1 = output data High pass filtered. Default value: 0.
Output buffer data format full scale. Default value: 00 (2g).
The default full scale value range is 2g and the high pass filter is disabled.
Table 20. Full Scale Range
FS1
FS0
Full Scale Range
0
0
2
0
1
4
1
0
8
1
1
Reserved
0x0F: HP_FILTER_CUTOFF High Pass Filter Register
This register sets the high-pass filter cut-off frequency for removal of the offset and slower changing acceleration data. The
output of this filter is indicated by the data registers (0x01-0x06) when bit 4 (HPF_OUT) of Register 0x0E is set. The filter cut-off
options change based on the data rate selected as shown in Table 22. For details of implementation on the high pass filter, refer
to Freescale application note AN4071.
0x0F HP_FILTER_CUTOFF: High Pass Filter Register (Read/Write)
Bit 7
Bit 6
0
0
Bit 5
Bit 4
Pulse_HPF_BYP Pulse_LPF_EN
Bit 3
Bit 2
Bit 1
Bit 0
0
0
SEL1
SEL0
Table 21. High Pass Filter Cut-off Register Descriptions
Pulse_HPF_BYP
Pulse_LPF_EN
SEL[1:0]
Bypass High Pass Filter (HPF) for Pulse Processing Function.
0: HPF enabled for Pulse Processing, 1: HPF Bypassed for Pulse Processing
Default value: 0.
Enable Low Pass Filter (LPF) for Pulse Processing Function.
0: LPF disabled for Pulse Processing, 1: LPF Enabled for Pulse Processing
Default value: 0.
HPF Cut-off frequency selection.
Default value: 00 (see Table 22).
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Table 22. High Pass Filter Cut-off Options
Oversampling Mode = Normal
SEL1
SEL0
800 Hz
400 Hz
200 Hz
100 Hz
50 Hz
12.5 Hz
6.25 Hz
1.56 Hz
0
0
16 Hz
16 Hz
8 Hz
4 Hz
2 Hz
2 Hz
2 Hz
2 Hz
0
1
8 Hz
8 Hz
4 Hz
2 Hz
1 Hz
1 Hz
1 Hz
1 Hz
1
0
4 Hz
4 Hz
2 Hz
1 Hz
0.5 Hz
0.5 Hz
0.5 Hz
0.5 Hz
1
1
2 Hz
2 Hz
1 Hz
0.5 Hz
0.25 Hz
0.25 Hz
0.25 Hz
0.25 Hz
Oversampling Mode = Low Noise Low Power
0
0
16 Hz
16 Hz
8 Hz
4 Hz
2 Hz
0.5 Hz
0.5 Hz
0.5 Hz
0
1
8 Hz
8 Hz
4 Hz
2 Hz
1 Hz
0.25 Hz
0.25 Hz
0.25 Hz
1
0
4 Hz
4 Hz
2 Hz
1 Hz
0.5 Hz
0.125 Hz
0.125 Hz
0.125 Hz
1
1
2 Hz
2 Hz
1 Hz
0.5 Hz
0.25 Hz
0.063 Hz
0.063 Hz
0.063 Hz
Oversampling Mode = High Resolution
0
0
16 Hz
16 Hz
16 Hz
16 Hz
16 Hz
16 Hz
16 Hz
16 Hz
0
1
8 Hz
8 Hz
8 Hz
8 Hz
8 Hz
8 Hz
8 Hz
8 Hz
1
0
4 Hz
4 Hz
4 Hz
4 Hz
4 Hz
4 Hz
4 Hz
4 Hz
1
1
2 Hz
2 Hz
2 Hz
2 Hz
2 Hz
2 Hz
2 Hz
2 Hz
Oversampling Mode = Low Power
0
0
16 Hz
8 Hz
4 Hz
2 Hz
1 Hz
0.25 Hz
0.25 Hz
0.25 Hz
0
1
8 Hz
4 Hz
2 Hz
1 Hz
0.5 Hz
0.125 Hz
0.125 Hz
0.125 Hz
1
0
4 Hz
2 Hz
1 Hz
0.5 Hz
0.25 Hz
0.063 Hz
0.063 Hz
0.063 Hz
1
1
2 Hz
1 Hz
0.5 Hz
0.25 Hz
0.125 Hz
0.031 Hz
0.031 Hz
0.031 Hz
6.3
Portrait/Landscape Embedded Function Registers
For more details on the meaning of the different user configurable settings and for example code refer to Freescale application
note AN4068.
0x10: PL_STATUS Portrait/Landscape Status Register
This status register can be read to get updated information on any change in orientation by reading Bit 7, or on the specifics
of the orientation by reading the other bits. For further understanding of Portrait Up, Portrait Down, Landscape Left, Landscape
Right, Back and Front orientations please refer to Figure 3. The interrupt is cleared when reading the PL_STATUS register.
0x10 PL_STATUS Register (Read Only)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
NEWLP
LO
—
—
—
LAPO[1]
LAPO[0]
BAFRO
Table 23. PL_STATUS Register Description
NEWLP
Landscape/Portrait status change flag. Default value: 0.
0: No change, 1: BAFRO and/or LAPO and/or Z-Tilt lockout value has changed
LO
Z-Tilt Angle Lockout. Default value: 0.
0: Lockout condition has not been detected.
1: Z-Tilt lockout trip angle has been exceeded. Lockout has been detected.
LAPO[1:0](1)
Landscape/Portrait orientation. Default value: 00
00: Portrait Up: Equipment standing vertically in the normal orientation
01: Portrait Down: Equipment standing vertically in the inverted orientation
10: Landscape Right: Equipment is in landscape mode to the right
11: Landscape Left: Equipment is in landscape mode to the left.
BAFRO
Back or Front orientation. Default value: 0
0: Front: Equipment is in the front facing orientation.
1: Back: Equipment is in the back facing orientation.
1. The default power up state is BAFRO = 0, LAPO = 0, and LO = 0.
NEWLP is set to 1 after the first orientation detection after a STANDBY to ACTIVE transition, and whenever a change in LO,
BAFRO, or LAPO occurs. NEWLP bit is cleared anytime PL_STATUS register is read. The Orientation mechanism state change
is limited to a maximum 1.25g. LAPO BAFRO and LO continue to change when NEWLP is set. The current position is locked if
the absolute value of the acceleration experienced on any of the three axes is greater than 1.25g.
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0x11 Portrait/Landscape Configuration Register
This register enables the Portrait/Landscape function and sets the behavior of the debounce counter.
0x11 PL_CFG Register (Read/Write
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DBCNTM
PL_EN
—
—
—
—
—
—
Table 24. PL_CFG Description
DBCNTM
PL_EN
Debounce counter mode selection. Default value: 1
0: Decrements debounce whenever condition of interest is no longer valid.
1: Clears counter whenever condition of interest is no longer valid.
Portrait/Landscape Detection Enable. Default value: 0
0: Portrait/Landscape Detection is Disabled.
1: Portrait/Landscape Detection is Enabled.
0x12 Portrait/Landscape Debounce Counter
This register sets the debounce count for the orientation state transition. The minimum debounce latency is determined by the
data rate set by the product of the selected system ODR and PL_COUNT registers. Any transition from WAKE to SLEEP or vice
versa resets the internal Landscape/Portrait debounce counter. Note: The debounce counter weighting (time step) changes
based on the ODR and the Oversampling mode. Table 26 explains the time step value for all sample rates and all Oversampling
modes.
0x12 PL_COUNT Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DBNCE[7]
DBNCE[6]
DBNCE[5]
DBNCE[4]
DBNCE[3]
DBNCE[2]
DBNCE[1]
DBNCE[0]
Table 25. PL_COUNT Description
DBCNE[7:0]
Debounce Count value. Default value: 0000_0000.
Table 26. PL_COUNT Relationship with the ODR
ODR (Hz)
Max Time Range (s)
Time Step (ms)
Normal
LPLN
HighRes
LP
Normal
LPLN
HighRes
LP
800
0.319
0.319
0.319
0.319
1.25
1.25
1.25
1.25
400
0.638
0.638
0.638
0.638
2.5
2.5
2.5
2.5
200
1.28
1.28
0.638
1.28
5
5
2.5
5
100
2.55
2.55
0.638
2.55
10
10
2.5
10
50
5.1
5.1
0.638
5.1
20
20
2.5
20
12.5
5.1
20.4
0.638
20.4
20
80
2.5
80
6.25
5.1
20.4
0.638
40.8
20
80
2.5
160
1.56
5.1
20.4
0.638
40.8
20
80
2.5
160
0x13: PL_BF_ZCOMP Back/Front and Z Compensation Register
The Z-Lock angle compensation bits allow the user to adjust the Z-lockout region from 14° up to 43°. The default Z-lockout angle
is set to the default value of 29° upon power up. The Back to Front trip angle is set by default to ±75° but this angle also can be
adjusted from a range of 65° to 80° with 5° step increments.
0x13: PL_BF_ZCOMP Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
BKFR[1]
BKFR[0]
—
—
—
ZLOCK[2]
ZLOCK[1]
ZLOCK[0]
Table 27. PL_BF_ZCOMP Description
BKFR[7:6]
ZLOCK[2:0]
Back/Front Trip Angle Threshold. Default: 01 ≥ ±75°. Step size is 5°.
Range: ±(65° to 80°).
Z-Lock Angle Threshold. Range is from 14° to 43°. Step size is 4°.
Default value: 100 ≥ 29°. Maximum value: 111 ≥ 43°.
Note: All angles are accurate to ±2°.
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Table 28. Z-Lock Threshold Angles
Z-Lock Value
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
Threshold Angle
14°
18°
21°
25°
29°
33°
37°
42°
Table 29. Back/Front Orientation Definition
BKFR
Back/Front Transition
Front/Back Transition
00
Z < 80° or Z > 280°
Z > 100° and Z < 260°
01
Z < 75° or Z > 285°
Z > 105° and Z < 255°
10
Z < 70° or Z > 290°
Z > 110° and Z < 250°
11
Z < 65° or Z > 295°
Z > 115° and Z < 245°
0x14: P_L_THS_REG Portrait/Landscape Threshold and Hysteresis Register
This register represents the Portrait to Landscape trip threshold register used to set the trip angle for transitioning from Portrait
to Landscape and Landscape to Portrait. This register includes a value for the hysteresis.
0x14: P_L_THS_REG Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
P_L_THS[4]
P_L_THS[3]
P_L_THS[2]
P_L_THS[1]
P_L_THS[0]
HYS[2]
HYS[1]
HYS[0]
:
Table 30. P_L_THS_REG Description
P_L_THS[7:3]
HYS[2:0]
Portrait/Landscape trip threshold angle from 15° to 75°. See Table 31 for the values with the corresponding approximate
threshold angle. Default value: 1_0000 (45°).
This angle is added to the threshold angle for a smoother transition from Portrait to Landscape and Landscape to Portrait.
This angle ranges from 0° to ±24°. The default is 100 (±14°).
Table 31 is a look-up table to set the threshold. This is the center value that will be set for the trip point from Portrait to
Landscape and Landscape to Portrait. The default Trip Angle is 45° (0x10). The default hysteresis is ±14°.
Note: THS + HYS > 0 and THS + HYS < 32 for the Landscape/Portrait detection to work correctly. All angles are accurate to ±2°.
Table 31. Threshold Angle Thresholds Look-up Table
Threshold Angle (approx.)
5-bit
Register value
15°
0x07
20°
0x09
30°
0x0C
35°
0x0D
40°
0x0F
45°
0x10
55°
0x13
60°
0x14
70°
0x17
75°
0x19
Table 32. Trip Angles with Hysteresis for 45° Angle
Hysteresis
Register Value
0
1
2
3
4
5
6
7
Hysteresis
± Angle Range
±0
±4
±7
±11
±14
±17
±21
±24
Landscape to Portrait
Trip Angle
45°
49°
52°
56°
59°
62°
66°
69°
Portrait to Landscape
Trip Angle
45°
41°
38°
34°
31°
28°
24°
21°
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6.4
Motion and Freefall Embedded Function Registers
The freefall/motion function can be configured in either Freefall or Motion Detection mode via the OAE configuration bit (0x15
bit 6). The freefall/motion detection block can be disabled by setting all three bits ZEFE, YEFE, and XEFE to zero.
Depending on the register bits ELE (0x15 bit 7) and OAE (0x15 bit 6), each of the freefall and motion detection block can
operate in four different modes:
Mode 1: Freefall Detection with ELE = 0, OAE = 0
In this mode, the EA bit (0x16 bit 7) indicates a freefall event after the debounce counter is complete. The ZEFE, YEFE, and
XEFE control bits determine which axes are considered for the freefall detection. Once the EA bit is set, and DBCNTM = 0, the
EA bit can get cleared only after the delay specified by FF_MT_COUNT. This is because the counter is in decrement mode. If
DBCNTM = 1, the EA bit is cleared as soon as the freefall condition disappears, and will not be set again before the delay
specified by FF_MT_COUNT has passed. Reading the FF_MT_SRC register does not clear the EA bit. The event flags (0x16)
ZHE, ZHP, YHE, YHP, XHE, and XHP reflect the motion detection status (i.e. high g event) without any debouncing, provided that
the corresponding bits ZEFE, YEFE, and/or XEFE are set.
Mode 2: Freefall Detection with ELE = 1, OAE = 0
In this mode, the EA event bit indicates a freefall event after the debounce counter. Once the debounce counter reaches the
time value for the set threshold, the EA bit is set, and remains set until the FF_MT_SRC register is read. When the FF_MT_SRC
register is read, the EA bit and the debounce counter are cleared and a new event can only be generated after the delay specified
by FF_MT_CNT. The ZEFE, YEFE, and XEFE control bits determine which axes are considered for the freefall detection. While
EA = 0, the event flags ZHE, ZHP, YHE, YHP, XHE, and XHP reflect the motion detection status (i.e., high g event) without any
debouncing, provided that the corresponding bits ZEFE, YEFE, and/or XEFE are set. The event flags ZHE, ZHP, YHE, YHP, XHE,
and XHP are latched when the EA event bit is set. The event flags ZHE, ZHP, YHE, YHP, XHE, and XHP will start changing only
after the FF_MT_SRC register has been read.
Mode 3: Motion Detection with ELE = 0, OAE = 1
In this mode, the EA bit indicates a motion event after the debounce counter time is reached. The ZEFE, YEFE, and XEFE
control bits determine which axes are taken into consideration for motion detection. Once the EA bit is set, and DBCNTM = 0,
the EA bit can get cleared only after the delay specified by FF_MT_COUNT. If DBCNTM = 1, the EA bit is cleared as soon as the
motion high g condition disappears. The event flags ZHE, ZHP, YHE, YHP, XHE, and XHP reflect the motion detection status
(i.e., high g event) without any debouncing, provided that the corresponding bits ZEFE, YEFE, and/or XEFE are set. Reading the
FF_MT_SRC does not clear any flags, nor is the debounce counter reset.
Mode 4: Motion Detection with ELE = 1, OAE = 1
In this mode, the EA bit indicates a motion event after debouncing. The ZEFE, YEFE, and XEFE control bits determine which
axes are taken into consideration for motion detection. Once the debounce counter reaches the threshold, the EA bit is set, and
remains set until the FF_MT_SRC register is read. When the FF_MT_SRC register is read, all register bits are cleared and the
debounce counter are cleared and a new event can only be generated after the delay specified by FF_MT_CNT. While the bit
EA is zero, the event flags ZHE, ZHP, YHE, YHP, XHE, and XHP reflect the motion detection status (i.e., high g event) without
any debouncing, provided that the corresponding bits ZEFE, YEFE, and/or XEFE are set. When the EA bit is set, these bits keep
their current value until the FF_MT_SRC register is read.
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0x15 FF_MT_CFG Freefall/Motion Configuration Register
This is the Freefall/Motion configuration register for setting up the conditions of the freefall or motion function.
0x15 FF_MT_CFG Register (Read/Write)
Bit 7
ELE
Bit 6
OAE
Bit 5
ZEFE
Bit 4
YEFE
Bit 3
XEFE
Bit 2
—
Bit 1
—
Bit 0
—
Table 33. FF_MT_CFG Description
ELE
Event Latch Enable: Event flags are latched into FF_MT_SRC register. Reading of the FF_MT_SRC register clears the event
flag EA and all FF_MT_SRC bits. Default value: 0.
0: Event flag latch disabled; 1: event flag latch enabled
OAE
Motion detect / Freefall detect flag selection. Default value: 0. (Freefall Flag)
0: Freefall Flag (Logical AND combination)
1: Motion Flag (Logical OR combination)
ZEFE
Event flag enable on Z Default value: 0.
0: event detection disabled; 1: raise event flag on measured acceleration value beyond preset threshold
YEFE
Event flag enable on Y event. Default value: 0.
0: Event detection disabled; 1: raise event flag on measured acceleration value beyond preset threshold
XEFE
Event flag enable on X event. Default value: 0.
0: event detection disabled; 1: raise event flag on measured acceleration value beyond preset threshold
OAE bit allows the selection between Motion (logical OR combination) and Freefall (logical AND combination) detection.
ELE denotes whether the enabled event flag will to be latched in the FF_MT_SRC register or the event flag status in the
FF_MT_SRC will indicate the real-time status of the event. If ELE bit is set to a logic ‘1’, then the event flags are frozen when the
EA bit gets set, and are cleared by reading the FF_MT_SRC source register.
ZHFE, YEFE, XEFE enable the detection of a motion or freefall event when the measured acceleration data on X, Y, Z channel
is beyond the threshold set in FF_MT_THS register. If the ELE bit is set to logic ‘1’ in the FF_MT_CFG register new event flags
are blocked from updating the FF_MT_SRC register.
FF_MT_THS is the threshold register used to detect freefall motion events. The unsigned 7-bit FF_MT_THS threshold register
holds the threshold for the freefall detection where the magnitude of the X and Y and Z acceleration values is lower or equal than
the threshold value. Conversely, the FF_MT_THS also holds the threshold for the motion detection where the magnitude of the
X or Y or Z acceleration value is higher than the threshold value.
+8g
X, Y, Z High g Region
High g + Threshold (Motion)
Positive
Acceleration
Low g Threshold (Freefall)
X, Y, Z Low g Region
High g - Threshold (Motion)
X, Y, Z High g Region
Negative
Acceleration
-8g
Figure 13. FF_MT_CFG High and Low g Level
0x16 FF_MT_SRC Freefall/Motion Source Register
0x16: FF_MT_SRC Freefall and Motion Source Register (Read Only)
Bit 7
EA
Bit 6
—
Bit 5
ZHE
Bit 4
ZHP
Bit 3
YHE
Bit 2
YHP
Bit 1
XHE
Bit 0
XHP
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Table 34. Freefall/Motion Source Description
EA
ZHE
ZHP
YHE
YHP
XHE
XHP
Event Active Flag. Default value: 0.
0: No event flag has been asserted; 1: one or more event flag has been asserted.
See the description of the OAE bit to determine the effect of the 3-axis event flags on the EA bit.
Z Motion Flag. Default value: 0.
0: No Z Motion event detected, 1: Z Motion has been detected
This bit reads always zero if the ZEFE control bit is set to zero
Z Motion Polarity Flag. Default value: 0.
0: Z event was Positive g, 1: Z event was Negative g
This bit read always zero if the ZEFE control bit is set to zero
Y Motion Flag. Default value: 0.
0: No Y Motion event detected, 1: Y Motion has been detected
This bit read always zero if the YEFE control bit is set to zero
Y Motion Polarity Flag. Default value: 0
0: Y event detected was Positive g, 1: Y event was Negative g
This bit reads always zero if the YEFE control bit is set to zero
X Motion Flag. Default value: 0
0: No X Motion event detected, 1: X Motion has been detected
This bit reads always zero if the XEFE control bit is set to zero
X Motion Polarity Flag. Default value: 0
0: X event was Positive g, 1: X event was Negative g
This bit reads always zero if the XEFE control bit is set to zero
This register keeps track of the acceleration event which is triggering (or has triggered, in case of ELE bit in FF_MT_CFG
register being set to 1) the event flag. In particular EA is set to a logic ‘1’ when the logical combination of acceleration events
flags specified in FF_MT_CFG register is true. This bit is used in combination with the values in INT_EN_FF_MT and
INT_CFG_FF_MT register bits to generate the freefall/motion interrupts.
An X,Y, or Z motion is true when the acceleration value of the X or Y or Z channel is higher than the preset threshold value
defined in the FF_MT_THS register.
Conversely an X, Y, and Z low event is true when the acceleration value of the X and Y and Z channel is lower than or equal
to the preset threshold value defined in the FF_MT_THS register.
0x17: FF_MT_THS Freefall and Motion Threshold Register
0x17 FF_MT_THS Register (Read/Write)
Bit 7
DBCNTM
Bit 6
THS6
Bit 5
THS5
Bit 4
THS4
Bit 3
THS3
Bit 2
THS2
Bit 1
THS1
Bit 0
THS0
Table 35. FF_MT_THS Description
DBCNTM
Debounce counter mode selection. Default value: 0.
0: increments or decrements debounce, 1: increments or clears counter.
THS[6:0]
Freefall /Motion Threshold: Default value: 000_0000.
The threshold resolution is 0.063g/LSB and the threshold register has a range of 0 to 127 counts. The maximum range is to
8g. Note that even when the full scale value is set to 2g or 4g the motion detects up to 8g. If the Low Noise bit is set in Register
0x2A then the maximum threshold will be limited to 4g regardless of the full scale range.
DBCNTM bit configures the way in which the debounce counter is reset when the inertial event of interest is momentarily not
true.
When DBCNTM bit is a logic ‘1’, the debounce counter is cleared to 0 whenever the inertial event of interest is no longer true
as shown in Figure 14, (b). While the DBCNTM bit is set to logic ‘0’ the debounce counter is decremented by 1 whenever the
inertial event of interest is no longer true (Figure 14, (c)) until the debounce counter reaches 0 or the inertial event of interest
becomes active.
Decrementing the debounce counter acts as a median enabling the system to filter out irregular spurious events which might
impede the detection of inertial events.
MMA8451Q
34
Sensors
Freescale Semiconductor
0x18 FF_MT_COUNT Debounce Register
This register sets the number of debounce sample counts for the event trigger.
0x18 FF_MT_COUNT_Register (Read/Write)
Bit 7
D7
Bit 6
D6
Bit 5
D5
Bit 4
D4
Bit 3
D3
Bit 2
D2
Bit 1
D1
Bit 0
D0
Table 36. FF_MT_COUNT Description
D[7:0]
Count value. Default value: 0000_0000
This register sets the minimum number of debounce sample counts of continuously matching the detection condition user
selected for the freefall, motion event.
When the internal debounce counter reaches the FF_MT_COUNT value a Freefall/Motion event flag is set. The debounce
counter will never increase beyond the FF_MT_COUNT value. Time step used for the debounce sample count depends on the
ODR chosen and the Oversampling mode as shown in Table 37.
Table 37. FF_MT_COUNT Relationship with the ODR
ODR (Hz)
Max Time Range (s)
Time Step (ms)
Normal
LPLN
HighRes
LP
Normal
LPLN
HighRes
LP
800
0.319
0.319
0.319
0.319
1.25
1.25
1.25
1.25
400
0.638
0.638
0.638
0.638
2.5
2.5
2.5
2.5
200
1.28
1.28
0.638
1.28
5
5
2.5
5
100
2.55
2.55
0.638
2.55
10
10
2.5
10
50
5.1
5.1
0.638
5.1
20
20
2.5
20
12.5
5.1
20.4
0.638
20.4
20
80
2.5
80
6.25
5.1
20.4
0.638
40.8
20
80
2.5
160
1.56
5.1
20.4
0.638
40.8
20
80
2.5
160
MMA8451Q
Sensors
Freescale Semiconductor
35
High g Event on
all 3-axis
(Motion Detect)
Count Threshold
(a)
FF
Counter
Value
FFEA
High g Event on
all 3-axis
(Motion Detect)
DBCNTM = 1
Count Threshold
Debounce
Counter
Value
(b)
EA
High g Event on
all 3-axis
(Motion Detect)
DBCNTM = 0
Count Threshold
Debounce
Counter
Value
(c)
EA
Figure 14. DBCNTM Bit Function
MMA8451Q
36
Sensors
Freescale Semiconductor
6.5
Transient (HPF) Acceleration Detection
For more information on the uses of the transient function please review application note AN4071. This function is similar to
the motion detection except that high pass filtered data is compared. There is an option to disable the high pass filter through the
function. In this case the behavior is the same as the motion detection. This allows for the device to have 2 motion detection
functions.
0x1D: Transient_CFG Register
The transient detection mechanism can be configured to raise an interrupt when the magnitude of the high pass filtered
acceleration threshold is exceeded. The TRANSIENT_CFG register is used to enable the transient interrupt generation
mechanism for the 3 axes (X, Y, Z) of acceleration. There is also an option to bypass the high pass filter. When the high pass
filter is bypassed, the function behaves similar to the motion detection.
0x1D TRANSIENT_CFG Register (Read/Write)
Bit 7
—
Bit 6
—
Bit 5
—
Bit 4
ELE
Bit 3
ZTEFE
Bit 2
YTEFE
Bit 1
XTEFE
Bit 0
HPF_BYP
Table 38. TRANSIENT_CFG Description
Transient event flags are latched into the TRANSIENT_SRC register. Reading of the TRANSIENT_SRC register clears the event
flag. Default value: 0.
0: Event flag latch disabled; 1: Event flag latch enabled
ELE
ZTEFE
Event flag enable on Z transient acceleration greater than transient threshold event. Default value: 0.
0: Event detection disabled; 1: Raise event flag on measured acceleration delta value greater than transient threshold.
YTEFE
Event flag enable on Y transient acceleration greater than transient threshold event. Default value: 0.
0: Event detection disabled; 1: Raise event flag on measured acceleration delta value greater than transient threshold.
XTEFE
Event flag enable on X transient acceleration greater than transient threshold event. Default value: 0.
0: Event detection disabled; 1: Raise event flag on measured acceleration delta value greater than transient threshold.
HPF_BYP
Bypass High Pass filter Default value: 0.
0: Data to transient acceleration detection block is through HPF 1: Data to transient acceleration detection block is NOT through
HPF (similar to motion detection function)
0x1E TRANSIENT_SRC Register
The Transient Source register provides the status of the enabled axes and the polarity (directional) information. When this
register is read it clears the interrupt for the transient detection. When new events arrive while EA = 1, additional *TRANSE bits
may get set, and the corresponding *_Trans_Pol flag become updated. However no *TRANSE bit may get cleared before the
TRANSIENT_SRC register is read.
0x1E TRANSIENT_SRC Register (Read Only)
Bit 7
—
Bit 6
EA
Bit 5
ZTRANSE
Bit 4
Z_Trans_Pol
Bit 3
YTRANSE
Bit 2
Y_Trans_Pol
Bit 1
XTRANSE
Bit 0
X_Trans_Pol
Table 39. TRANSIENT_SRC Description
EA
ZTRANSE
Z_Trans_Pol
YTRANSE
Y_Trans_Pol
XTRANSE
X_Trans_Pol
Event Active Flag. Default value: 0.
0: no event flag has been asserted; 1: one or more event flag has been asserted.
Z transient event. Default value: 0.
0: no interrupt, 1: Z Transient acceleration greater than the value of TRANSIENT_THS event has occurred
Polarity of Z Transient Event that triggered interrupt. Default value: 0.
0: Z event was Positive g, 1: Z event was Negative g
Y transient event. Default value: 0.
0: no interrupt, 1: Y Transient acceleration greater than the value of TRANSIENT_THS event has occurred
Polarity of Y Transient Event that triggered interrupt. Default value: 0.
0: Y event was Positive g, 1: Y event was Negative g
X transient event. Default value: 0.
0: no interrupt, 1: X Transient acceleration greater than the value of TRANSIENT_THS event has occurred
Polarity of X Transient Event that triggered interrupt. Default value: 0.
0: X event was Positive g, 1: X event was Negative g
When the EA bit gets set while ELE = 1, all other status bits get frozen at their current state. By reading the TRANSIENT_SRC
register, all bits get cleared.
MMA8451Q
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Freescale Semiconductor
37
0x1F TRANSIENT_THS Register
The Transient Threshold register sets the threshold limit for the detection of the transient acceleration. The value in the
TRANSIENT_THS register corresponds to a g value which is compared against the values of High Pass Filtered Data. If the High
Pass Filtered acceleration value exceeds the threshold limit an event flag is raised and the interrupt is generated if enabled.
0x1F TRANSIENT_THS Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DBCNTM
THS6
THS5
THS4
THS3
THS2
THS1
THS0
Table 40. TRANSIENT_THS Description
DBCNTM
Debounce counter mode selection. Default value: 0. 0: increments or decrements debounce; 1: increments or clears counter.
THS[6:0]
Transient Threshold: Default value: 000_0000.
The threshold THS[6:0] is a 7-bit unsigned number, 0.063g/LSB.The minimum threshold resolution is dependent on the
selected acceleration g range and the threshold register has a range of 1 to 127. Therefore the minimum threshold resolution is
0.063g/LSB. The maximum threshold is 8g. Even if the part is set to full scale at 2g or 4g this function will still operate up to 8g.
If the Low Noise bit is set in Register 0x2A the maximum threshold to be reached is 4g.
0x20 TRANSIENT_COUNT
The TRANSIENT_COUNT sets the minimum number of debounce counts continuously matching the condition where the
unsigned value of high pass filtered data is greater than the user specified value of TRANSIENT_THS.
0x20 TRANSIENT_COUNT Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
D7
D6
D5
D4
D3
D2
D1
D0
Table 41. TRANSIENT_COUNT Description
D[7:0]
Count value. Default value: 0000_0000.
The time step for the transient detection debounce counter is set by the value of the system ODR and the Oversampling mode.
Table 42. TRANSIENT_COUNT Relationship with the ODR
ODR (Hz)
Max Time Range (s)
Time Step (ms)
Normal
LPLN
HighRes
LP
Normal
LPLN
HighRes
LP
800
0.319
0.319
0.319
0.319
1.25
1.25
1.25
1.25
400
0.638
0.638
0.638
0.638
2.5
2.5
2.5
2.5
200
1.28
1.28
0.638
1.28
5
5
2.5
5
100
2.55
2.55
0.638
2.55
10
10
2.5
10
50
5.1
5.1
0.638
5.1
20
20
2.5
20
12.5
5.1
20.4
0.638
20.4
20
80
2.5
80
6.25
5.1
20.4
0.638
40.8
20
80
2.5
160
1.56
5.1
20.4
0.638
40.8
20
80
2.5
160
MMA8451Q
38
Sensors
Freescale Semiconductor
6.6
Single, Double and Directional Tap Detection Registers
For more details of how to configure the tap detection and sample code please refer to Freescale application note, AN4072.
The tap detection registers are referred to as “Pulse”.
0x21: PULSE_CFG Pulse Configuration Register
This register configures the event flag for the tap detection for enabling/disabling the detection of a single and double pulse
on each of the axes.
0x21 PULSE_CFG Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DPA
ELE
ZDPEFE
ZSPEFE
YDPEFE
YSPEFE
XDPEFE
XSPEFE
Table 43. PULSE_CFG Description
DPA
Double Pulse Abort. Default value: 0.
0: Double Pulse detection is not aborted if the start of a pulse is detected during the time period specified by the PULSE_LTCY register.
1: Setting the DPA bit momentarily suspends the double tap detection if the start of a pulse is detected during the time period specified
by the PULSE_LTCY register and the pulse ends before the end of the time period specified by the PULSE_LTCY register.
ELE
Pulse event flags are latched into the PULSE_SRC register. Reading of the PULSE_SRC register clears the event flag.
Default value: 0.
0: Event flag latch disabled; 1: Event flag latch enabled
ZDPEFE
ZSPEFE
YDPEFE
YSPEFE
XDPEFE
XSPEFE
Event flag enable on double pulse event on Z-axis. Default value: 0.
0: Event detection disabled; 1: Event detection enabled
Event flag enable on single pulse event on Z-axis. Default value: 0.
0: Event detection disabled; 1: Event detection enabled
Event flag enable on double pulse event on Y-axis. Default value: 0.
0: Event detection disabled; 1: Event detection enabled
Event flag enable on single pulse event on Y-axis. Default value: 0.
0: Event detection disabled; 1: Event detection enabled
Event flag enable on double pulse event on X-axis. Default value: 0.
0: Event detection disabled; 1: Event detection enabled
Event flag enable on single pulse event on X-axis. Default value: 0.
0: Event detection disabled; 1: Event detection enabled
0x22: PULSE_SRC Pulse Source Register
This register indicates a double or single pulse event has occurred and also which direction. The corresponding axis and event
must be enabled in Register 0x21 for the event to be seen in the source register.
0x22 PULSE_SRC Register (Read Only)
Bit 7
EA
Bit 6
AxZ
Bit 5
AxY
Bit 4
AxX
Bit 3
DPE
Bit 2
PolZ
Bit 1
PolY
Bit 0
PolX
Table 44. PULSE_SRC Description
EA
AxZ
AxY
AxX
DPE
PolZ
PolY
PolX
Event Active Flag. Default value: 0.
(0: No interrupt has been generated; 1: One or more interrupt events have been generated)
Z-axis event. Default value: 0.
(0: No interrupt; 1: Z-axis event has occurred)
Y-axis event. Default value: 0.
(0: No interrupt; 1: Y-axis event has occurred)
X-axis event. Default value: 0.
(0: No interrupt; 1: X-axis event has occurred)
Double pulse on first event. Default value: 0.
(0: Single Pulse Event triggered interrupt; 1: Double Pulse Event triggered interrupt)
Pulse polarity of Z-axis Event. Default value: 0.
(0: Pulse Event that triggered interrupt was Positive; 1: Pulse Event that triggered interrupt was negative)
Pulse polarity of Y-axis Event. Default value: 0.
(0: Pulse Event that triggered interrupt was Positive; 1: Pulse Event that triggered interrupt was negative)
Pulse polarity of X-axis Event. Default value: 0.
(0: Pulse Event that triggered interrupt was Positive; 1: Pulse Event that triggered interrupt was negative)
When the EA bit gets set while ELE = 1, all status bits (AxZ, AxY, AxZ, DPE, and PolX, PolY, PolZ) are frozen. Reading the
PULSE_SRC register clears all bits. Reading the source register will clear the interrupt.
MMA8451Q
Sensors
Freescale Semiconductor
39
0x23 - 0x25: PULSE_THSX, Y, Z Pulse Threshold for X, Y & Z Registers
The pulse threshold can be set separately for the X, Y and Z axes. The PULSE_THSX, PULSE_THSY and PULSE_THSZ
registers define the threshold which is used by the system to start the pulse detection procedure.
0x23 PULSE_THSX Register (Read/Write)
Bit 7
0
Bit 6
THSX6
Bit 5
THSX5
Bit 4
THSX4
Bit 3
THSX3
Bit 2
THSX2
Bit 1
THSX1
Bit 0
THSX0
Bit 2
THSY2
Bit 1
THSY1
Bit 0
THSY0
Table 45. PULSE_THSX Description
THSX[6:0]
Pulse Threshold on X-axis. Default value: 000_0000.
0x24 PULSE_THSY Register (Read/Write)
Bit 7
0
Bit 6
THSY6
Bit 5
THSY5
Bit 4
THSY4
Bit 3
THSY3
Table 46. PULSE_THSY Description
THSY[6:0]
Pulse Threshold on Y-axis. Default value: 000_0000.
0x25 PULSE_THSZ Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
THSZ6
THSZ5
THSZ4
THSZ3
THSZ2
THSZ1
THSZ0
Table 47. PULSE_THSZ Description
THSZ[6:0]
Pulse Threshold on Z-axis. Default value: 000_0000.
The threshold values range from 1 to 127 with steps of 0.63g/LSB at a fixed 8g acceleration range, thus the minimum
resolution is always fixed at 0.063g/LSB. If the Low Noise bit in Register 0x2A is set then the maximum threshold will be 4g. The
PULSE_THSX, PULSE_THSY and PULSE_THSZ registers define the threshold which is used by the system to start the pulse
detection procedure. The threshold value is expressed over 7-bits as an unsigned number.
0x26: PULSE_TMLT Pulse Time Window 1 Register
0x26 PULSE_TMLT Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TMLT7
TMLT6
TMLT5
TMLT4
TMLT3
TMLT2
TMLT1
TMLT0
Table 48. PULSE_TMLT Description
TMLT[7:0]
Pulse Time Limit. Default value: 0000_0000.
The bits TMLT7 through TMLT0 define the maximum time interval that can elapse between the start of the acceleration on the
selected axis exceeding the specified threshold and the end when the acceleration on the selected axis must go below the
specified threshold to be considered a valid pulse.
The minimum time step for the pulse time limit is defined in Table 49 and Table 50. Maximum time for a given ODR and
Oversampling mode is the time step pulse multiplied by 255. The time steps available are dependent on the Oversampling mode
and whether the Pulse Low Pass Filter option is enabled or not. The Pulse Low Pass Filter is set in Register 0x0F.
Table 49. Time Step for PULSE Time Limit (Reg 0x0F) Pulse_LPF_EN = 1
ODR (Hz)
Max Time Range (s)
Time Step (ms)
Normal
LPLN
HighRes
LP
Normal
LPLN
HighRes
LP
800
0.319
0.319
0.319
0.319
1.25
1.25
1.25
1.25
400
0.638
0.638
0.638
0.638
2.5
2.5
2.5
2.5
200
1.28
1.28
0.638
1.28
5
5
2.5
5
100
2.55
2.55
0.638
2.55
10
10
2.5
10
50
5.1
5.1
0.638
5.1
20
20
2.5
20
12.5
5.1
20.4
0.638
20.4
20
80
2.5
80
6.25
5.1
20.4
0.638
40.8
20
80
2.5
160
1.56
5.1
20.4
0.638
40.8
20
80
2.5
160
MMA8451Q
40
Sensors
Freescale Semiconductor
Table 50. Time Step for PULSE Time Limit (Reg 0x0F) Pulse_LPF_EN = 0
ODR (Hz)
Max Time Range (s)
Time Step (ms)
Normal
LPLN
HighRes
LP
Normal
LPLN
HighRes
LP
800
0.159
0.159
0.159
0.159
0.625
0.625
0.625
0.625
400
0.159
0.159
0.159
0.319
0.625
0.625
0.625
1.25
200
0.319
0.319
0.159
0.638
1.25
1.25
0.625
2.5
100
0.638
0.638
0.159
1.28
2.5
2.5
0.625
5
50
1.28
1.28
0.159
2.55
5
5
0.625
10
12.5
1.28
5.1
0.159
10.2
5
20
0.625
40
6.25
1.28
5.1
0.159
10.2
5
20
0.625
40
1.56
1.28
5.1
0.159
10.2
5
20
0.625
40
0x27: PULSE_LTCY Pulse Latency Timer Register
0x27 PULSE_LTCY Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
LTCY7
LTCY6
LTCY5
LTCY4
LTCY3
LTCY2
LTCY1
LTCY0
Table 51. PULSE_LTCY Description
LTCY[7:0]
Latency Time Limit. Default value: 0000_0000
The bits LTCY7 through LTCY0 define the time interval that starts after the first pulse detection. During this time interval, all
pulses are ignored. Note: This timer must be set for single pulse and for double pulse.
The minimum time step for the pulse latency is defined in Table 52 and Table 53. The maximum time is the time step at the ODR
and Oversampling mode multiplied by 255. The timing also changes when the Pulse LPF is enabled or disabled.
Table 52. Time Step for PULSE Latency @ ODR and Power Mode (Reg 0x0F) Pulse_LPF_EN = 1
ODR (Hz)
Max Time Range (s)
Normal
LPLN
HighRes
Time Step (ms)
LP
Normal
LPLN
HighRes
LP
800
0.638
0.638
0.638
0.638
2.5
2.5
2.5
2.5
400
1.276
1.276
1.276
1.276
5
5
5
5
200
2.56
2.56
1.276
2.56
10
10
5
10
100
5.1
5.1
1.276
5.1
20
20
5
20
50
10.2
10.2
1.276
10.2
40
40
5
40
12.5
10.2
40.8
1.276
40.8
40
160
5
160
6.25
10.2
40.8
1.276
81.6
40
160
5
320
1.56
10.2
40.8
1.276
81.6
40
160
5
320
Table 53. Time Step for PULSE Latency @ ODR and Power Mode (Reg 0x0F) Pulse_LPF_EN = 0
ODR (Hz)
Max Time Range (s)
Time Step (ms)
Normal
LPLN
HighRes
LP
Normal
LPLN
HighRes
LP
800
0.318
0.318
0.318
0.318
1.25
1.25
1.25
1.25
400
0.318
0.318
0.318
0.638
1.25
1.25
1.25
2.5
200
0.638
0.638
0.318
1.276
2.5
2.5
1.25
5
100
1.276
1.276
0.318
2.56
5
5
1.25
10
50
2.56
2.56
0.318
5.1
10
10
1.25
20
12.5
2.56
10.2
0.318
20.4
10
40
1.25
80
6.25
2.56
10.2
0.318
20.4
10
40
1.25
80
1.56
2.56
10.2
0.318
20.4
10
40
1.25
80
MMA8451Q
Sensors
Freescale Semiconductor
41
0x28 PULSE_WIND Register (Read/Write)
0x28: PULSE_WIND Second Pulse Time Window Register
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
WIND7
WIND6
WIND5
WIND4
WIND3
WIND2
WIND1
WIND0
Table 54. PULSE_WIND Description
WIND[7:0]
Second Pulse Time Window. Default value: 0000_0000.
The bits WIND7 through WIND0 define the maximum interval of time that can elapse after the end of the latency interval in which
the start of the second pulse event must be detected provided the device has been configured for double pulse detection. The
detected second pulse width must be shorter than the time limit constraints specified by the PULSE_TMLT register, but the end
of the double pulse need not finish within the time specified by the PULSE_WIND register.
The minimum time step for the pulse window is defined in Table 55 and Table 56. The maximum time is the time step at the ODR,
Oversampling mode and LPF Filter Option multiplied by 255.
Table 55. Time Step for PULSE Detection Window @ ODR and Power Mode (Reg 0x0F) Pulse_LPF_EN = 1
ODR (Hz)
Max Time Range (s)
Normal
LPLN
HighRes
Time Step (ms)
LP
Normal
LPLN
HighRes
LP
800
0.638
0.638
0.638
0.638
2.5
2.5
2.5
2.5
400
1.276
1.276
1.276
1.276
5
5
5
5
200
2.56
2.56
1.276
2.56
10
10
5
10
100
5.1
5.1
1.276
5.1
20
20
5
20
50
10.2
10.2
1.276
10.2
40
40
5
40
12.5
10.2
40.8
1.276
40.8
40
160
5
160
6.25
10.2
81.6
1.276
81.6
40
160
5
320
1.56
10.2
326
1.276
326
40
160
5
320
Table 56. Time Step for PULSE Detection Window @ ODR and Power Mode (Reg 0x0F) Pulse_LPF_EN = 0
ODR (Hz)
Max Time Range (s)
Time Step (ms)
Normal
LPLN
HighRes
LP
Normal
LPLN
HighRes
LP
800
0.318
0.318
0.318
0.318
1.25
1.25
1.25
1.25
400
0.318
0.318
0.318
0.638
1.25
1.25
1.25
2.5
200
0.638
0.638
0.318
1.276
2.5
2.5
1.25
5
100
1.276
1.276
0.318
2.56
5
5
1.25
10
50
2.56
2.56
0.318
5.1
10
10
1.25
20
12.5
2.56
10.2
0.318
20.4
10
40
1.25
80
6.25
2.56
10.2
0.318
20.4
10
40
1.25
80
1.56
2.56
10.2
0.318
20.4
10
40
1.25
80
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6.7
Auto-WAKE/SLEEP Detection
The ASLP_COUNT register sets the minimum time period of inactivity required to change current ODR value from the value
specified in the DR[2:0] register to ASLP_RATE register value, provided the SLPE bit is set to a logic ‘1’ in the CTRL_REG2
register. See Table 52 for functional blocks that may be monitored for inactivity in order to trigger the “return to SLEEP” event.
0x29 ASLP_COUNT Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
D7
D6
D5
D4
D3
D2
D1
D0
Table 57. ASLP_COUNT Description
D[7:0]
Duration value. Default value: 0000_0000.
D7-D0 defines the minimum duration time to change current ODR value from DR to ASLP_RATE. Time step and maximum
value depend on the ODR chosen as shown in Table 58.
Table 58. ASLP_COUNT Relationship with ODR
Output Data Rate
(ODR)
Duration
ODR Time Step
ASLP_COUNT Step
800 Hz
0 to 81s
1.25 ms
320 ms
400 Hz
0 to 81s
2.5 ms
320 ms
200 Hz
0 to 81s
5 ms
320 ms
100 Hz
0 to 81s
10 ms
320 ms
50 Hz
0 to 81s
20 ms
320 ms
12.5 Hz
0 to 81s
80 ms
320 ms
6.25 Hz
0 to 81s
160 ms
320 ms
1.56 Hz
0 to 162s
640 ms
640 ms
Table 59. SLEEP/WAKE Mode Gates and Triggers
Interrupt Source
Event restarts timer and
delays Return to SLEEP
Event will WAKE from SLEEP
FIFO_GATE
Yes
No
SRC_TRANS
Yes
Yes
SRC_LNDPRT
Yes
Yes
SRC_PULSE
Yes
Yes
SRC_FF_MT
Yes
Yes
SRC_ASLP
No*
No*
SRC_DRDY
No
No
* If the FIFO_GATE bit is set to logic ‘1’, the assertion of the SRC_ASLP interrupt does not prevent
the system from transitioning to SLEEP or from WAKE mode; instead it prevents the FIFO buffer from
accepting new sample data until the host application flushes the FIFO buffer.
In order to wake the device, the desired function or functions must be enabled in CTRL_REG4 and set to WAKE to SLEEP in
CTRL_REG3. All enabled functions will still function in SLEEP mode at the SLEEP ODR. Only the functions that have been
selected for WAKE from SLEEP will WAKE the device.
MMA8451Q has 4 functions that can be used to keep the sensor from falling asleep namely, Transient, Orientation, Tap and
Motion/Freefall. One or more of these functions can be enabled. In order to WAKE the device, 4 functions are provided namely,
Transient, Orientation, Tap, and the Motion/Freefall. Note that the FIFO does not WAKE the device. The Auto-WAKE/SLEEP
interrupt does not affect the WAKE/SLEEP, nor does the data ready interrupt. The FIFO gate (bit 7) in Register 0x2C, when set,
will hold the last data in the FIFO before transitioning to a different ODR. After the buffer is flushed, it will accept new sample data
at the current ODR. See Register 0x2C for the WAKE from SLEEP bits.
If the Auto-SLEEP bit is disabled, then the device can only toggle between STANDBY and WAKE mode. If Auto-SLEEP
interrupt is enabled, transitioning from ACTIVE mode to Auto-SLEEP mode and vice versa generates an interrupt.
MMA8451Q
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Freescale Semiconductor
43
6.8
Control Registers
Note: Except for STANDBY mode selection, the device must be in STANDBY mode to change any of the fields within
CTRL_REG1 (0x2A).
0x2A: CTRL_REG1 System Control 1 Register
0x2A CTRL_REG1 Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
ASLP_RATE1
ASLP_RATE0
DR2
DR1
DR0
LNOISE
F_READ
ACTIVE
Table 60. CTRL_REG1 Description
ASLP_RATE[1:0]
Configures the Auto-WAKE sample frequency when the device is in SLEEP Mode. Default value: 00.
See Table 61 for more information.
DR[2:0]
Data rate selection. Default value: 000.
See Table 62 for more information.
LNOISE
Reduced noise reduced Maximum range mode. Default value: 0.
(0: Normal mode; 1: Reduced Noise mode)
F_READ
Fast Read mode: Data format limited to single Byte Default value: 0.
(0: Normal mode 1: Fast Read Mode)
ACTIVE
Full Scale selection. Default value: 00.
(0: STANDBY mode; 1: ACTIVE mode)
Table 61. SLEEP Mode Rate Description
ASLP_RATE1
ASLP_RATE0
0
0
Frequency (Hz)
50
0
1
12.5
1
0
6.25
1
1
1.56
It is important to note that when the device is Auto-SLEEP mode, the system ODR and the data rate for all the system
functional blocks are overridden by the data rate set by the ASLP_RATE field.
DR[2:0] bits select the Output Data Rate (ODR) for acceleration samples. The default value is 000 for a data rate of 800 Hz.
Table 62. System Output Data Rate Selection
DR2
DR1
DR0
ODR
Period
0
0
0
800 Hz
1.25 ms
0
0
1
400 Hz
2.5 ms
0
1
0
200 Hz
5 ms
0
1
1
100 Hz
10 ms
20 ms
1
0
0
50 Hz
1
0
1
12.5 Hz
80 ms
1
1
0
6.25 Hz
160 ms
1
1
1
1.56 Hz
640 ms
ACTIVE bit selects between STANDBY mode and ACTIVE mode. The default value is 0 for STANDBY mode.
Table 63. Full Scale Selection
Active
Mode
0
STANDBY
1
ACTIVE
LNoise bit selects between normal full dynamic range mode and a high sensitivity, Low Noise mode. In Low Noise mode the
maximum signal that can be measured is ±4g. Note: Any thresholds set above 4g will not be reached.
F_Read bit selects between normal and Fast Read mode. When selected, the auto increment counter will skip over the LSB data
bytes. Data read from the FIFO will skip over the LSB data, reducing the acquisition time. Note F_READ can only be changed
when FMODE = 00. The F_READ bit applies for both the output registers and the FIFO.
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Freescale Semiconductor
0x2B: CTRL_REG2 System Control 2 Register
0x2B CTRL_REG2 Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
ST
RST
0
SMODS1
SMODS0
SLPE
MODS1
MODS0
Table 64. CTRL_REG2 Description
Self-Test Enable. Default value: 0.
0: Self-Test disabled; 1: Self-Test enabled
ST
Software Reset. Default value: 0.
0: Device reset disabled; 1: Device reset enabled.
RST
SMODS[1:0]
SLEEP mode power scheme selection. Default value: 00.
See Table 65 and Table 66
Auto-SLEEP enable. Default value: 0.
0: Auto-SLEEP is not enabled;
1: Auto-SLEEP is enabled.
SLPE
MODS[1:0]
ACTIVE mode power scheme selection. Default value: 00.
See Table 65 and Table 66
ST bit activates the self-test function. When ST is set, X, Y, and Z outputs will shift. RST bit is used to activate the software reset.
The reset mechanism can be enabled in STANDBY and ACTIVE mode.
When the reset bit is enabled, all registers are rest and are loaded with default values. Writing ‘1’ to the RST bit immediately
resets the device, no matter whether it is in ACTIVE/WAKE, ACTIVE/SLEEP, or STANDBY mode.
The I2C communication system is reset to avoid accidental corrupted data access.
At the end of the boot process the RST bit is de-asserted to 0. Reading this bit will return a value of zero.
The (S)MODS[1:0] bits select which Oversampling mode is to be used shown in Table 65. The Oversampling modes are
available in both WAKE Mode MOD[1:0] and also in the SLEEP Mode SMOD[1:0].
Table 65. MODS Oversampling Modes
(S)MODS1
(S)MODS0
0
0
Power Mode
Normal
0
1
Low Noise Low Power
1
0
High Resolution
1
1
Low Power
Table 66. MODS Oversampling Modes Current Consumption and Averaging Values at each ODR
Mode
Normal (00)
Low Noise Low Power (01)
High Resolution (10)
Low Power (11)
ODR
Current μA
OS Ratio
Current μA
OS Ratio
Current μA
OS Ratio
Current μA
OS Ratio
1.56 Hz
24
128
8
32
165
1024
6
16
6.25 Hz
24
32
8
8
165
256
6
4
12.5 Hz
24
16
8
4
165
128
6
2
50 Hz
24
4
24
4
165
32
14
2
100 Hz
44
4
44
4
165
16
24
2
200 Hz
85
4
85
4
165
8
44
2
400 Hz
165
4
165
4
165
4
85
2
800 Hz
165
2
165
2
165
2
165
2
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45
0x2C: CTRL_REG3 Interrupt Control Register
0x2C CTRL_REG3 Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
FIFO_GATE
WAKE_TRANS
WAKE_LNDPRT
WAKE_PULSE
WAKE_FF_MT
—
IPOL
PP_OD
Table 67. CTRL_REG3 Description
0: FIFO gate is bypassed. FIFO is flushed upon the system mode transitioning from WAKE to SLEEP mode or from SLEEP
to WAKE mode. Default value: 0.
1: The FIFO input buffer is blocked when transitioning from WAKE to SLEEP mode or from SLEEP to WAKE mode until the
FIFO is flushed. Although the system transitions from WAKE to SLEEP or from SLEEP to WAKE the contents of the FIFO
buffer are preserved, new data samples are ignored until the FIFO is emptied by the host application.
If the FIFO_GATE bit is set to logic ‘1’ and the FIFO buffer is not emptied before the arrival of the next sample, then the
FGERR bit in the SYS_MOD register (0x0B) will be asserted. The FGERR bit remains asserted as long as the FIFO buffer
remains un-emptied.
Emptying the FIFO buffer clears the FGERR bit in the SYS_MOD register.
FIFO_GATE
WAKE_TRANS
WAKE_LNDPRT
WAKE_PULSE
WAKE_FF_MT
IPOL
PP_OD
0:
1:
0:
1:
Transient function is bypassed in SLEEP mode. Default value: 0.
Transient function interrupt can wake up system
Orientation function is bypassed in SLEEP mode. Default value: 0.
Orientation function interrupt can wake up system
0: Pulse function is bypassed in SLEEP mode. Default value: 0.
1: Pulse function interrupt can wake up system
0: Freefall/Motion function is bypassed in SLEEP mode. Default value: 0.
1: Freefall/Motion function interrupt can wake up
Interrupt polarity ACTIVE high, or ACTIVE low. Default value: 0.
0: ACTIVE low; 1: ACTIVE high
Push-Pull/Open Drain selection on interrupt pad. Default value: 0.
0: Push-Pull; 1: Open Drain
IPOL bit selects the polarity of the interrupt signal. When IPOL is ‘0’ (default value) any interrupt event will signaled with a
logical 0.
PP_OD bit configures the interrupt pin to Push-Pull or in Open Drain mode. The default value is 0 which corresponds to PushPull mode. The Open Drain configuration can be used for connecting multiple interrupt signals on the same interrupt line.
0x2D: CTRL_REG4 Register (Read/Write)
0x2D CTRL_REG4 Register (Read/Write)
Bit 7
INT_EN_ASLP
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
INT_EN_FIFO INT_EN_TRANS INT_EN_LNDPR INT_EN_PULSE INT_EN_FF_MT
Bit 1
Bit 0
—
INT_EN_DRDY
Table 68. Interrupt Enable Register Description
Interrupt Enable
INT_EN_ASLP
INT_EN_FIFO
INT_EN_TRANS
INT_EN_LNDPRT
Description
Interrupt Enable. Default value: 0.
0: Auto-SLEEP/WAKE interrupt disabled; 1: Auto-SLEEP/WAKE interrupt enabled.
Interrupt Enable. Default value: 0.
0: FIFO interrupt disabled; 1: FIFO interrupt enabled.
Interrupt Enable. Default value: 0.
0: Transient interrupt disabled; 1: Transient interrupt enabled.
Interrupt Enable. Default value: 0.
0: Orientation (Landscape/Portrait) interrupt disabled.
1: Orientation (Landscape/Portrait) interrupt enabled.
INT_EN_PULSE
Interrupt Enable. Default value: 0.
0: Pulse Detection interrupt disabled; 1: Pulse Detection interrupt enabled
INT_EN_FF_MT
Interrupt Enable. Default value: 0.
0: Freefall/Motion interrupt disabled; 1: Freefall/Motion interrupt enabled
INT_EN_DRDY
Interrupt Enable. Default value: 0.
0: Data Ready interrupt disabled; 1: Data Ready interrupt enabled
The corresponding functional block interrupt enable bit allows the functional block to route its event detection flags to the
system’s interrupt controller. The interrupt controller routes the enabled functional block interrupt to the INT1 or INT2 pin.
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0x2E CTRL_REG5 Register (Read/Write)
0x2E: CTRL_REG5 Interrupt Configuration Register
Bit 7
Bit 6
INT_CFG_ASLP
INT_CFG_FIFO
Bit 5
Bit 4
Bit 3
Bit 2
INT_CFG_TRANS INT_CFG_LNDPRT INT_CFG_PULSE INT_CFG_FF_MT
Bit 1
Bit 0
—
INT_CFG_DRDY
Table 69. Interrupt Configuration Register Description
Interrupt Configuration
Description
INT1/INT2 Configuration. Default value: 0.
0: Interrupt is routed to INT2 pin; 1: Interrupt is routed to INT1 pin
INT1/INT2 Configuration. Default value: 0
0: Interrupt is routed to INT2 pin; 1: Interrupt is routed to INT1 pin
INT1/INT2 Configuration. Default value: 0.
0: Interrupt is routed to INT2 pin; 1: Interrupt is routed to INT1 pin
INT1/INT2 Configuration. Default value: 0.
0: Interrupt is routed to INT2 pin; 1: Interrupt is routed to INT1 pin
INT1/INT2 Configuration. Default value: 0.
0: Interrupt is routed to INT2 pin; 1: Interrupt is routed to INT1 pin
INT1/INT2 Configuration. Default value: 0.
0: Interrupt is routed to INT2 pin; 1: Interrupt is routed to INT1 pin
INT1/INT2 Configuration. Default value: 0.
0: Interrupt is routed to INT2 pin; 1: Interrupt is routed to INT1 pin
INT_CFG_ASLP
INT_CFG_FIFO
INT_CFG_TRANS
INT_CFG_LNDPRT
INT_CFG_PULSE
INT_CFG_FF_MT
INT_CFG_DRDY
The system’s interrupt controller shown in Figure 11 uses the corresponding bit field in the CTRL_REG5 register to determine
the routing table for the INT1 and INT2 interrupt pins. If the bit value is logic ‘0’ the functional block’s interrupt is routed to INT2,
and if the bit value is logic ‘1’ then the interrupt is routed to INT1. One or more functions can assert an interrupt pin; therefore a
host application responding to an interrupt should read the INT_SOURCE (0x0C) register to determine the appropriate sources
of the interrupt.
6.9
User Offset Correction Registers
For more information on how to calibrate the 0g Offset refer to AN4069 Offset Calibration Using the MMA8451Q. The 2’s
complement offset correction registers values are used to realign the Zero-g position of the X, Y, and Z-axis after device board
mount. The resolution of the offset registers is 2 mg per LSB. The 2’s complement 8-bit value would result in an offset
compensation range ±256 mg.
0x2F: OFF_X Offset Correction X Register
0x2F OFF_X Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
D7
D6
D5
D4
D3
D2
D1
D0
Table 70. OFF_X Description
D[7:0]
X-axis offset value. Default value: 0000_0000.
0x30: OFF_Y Offset Correction Y Register
0x30 OFF_Y Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
D7
D6
D5
D4
D3
D2
D1
D0
Table 71. OFF_Y Description
D[7:0]
Y-axis offset value. Default value: 0000_0000.
0x31: OFF_Z Offset Correction Z Register
0x31 OFF_Z Register (Read/Write)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
D7
D6
D5
D4
D3
D2
D1
D0
Table 72. OFF_Z Description
D[7:0]
Z-axis offset value. Default value: 0000_0000.
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Freescale Semiconductor
47
Table 73. MMA8451Q Register Map
Reg
Name
Definition
Bit 7
00
01
STATUS/F_STATUS
Data Status R
ZYXOW
ZOW
OUT_X_MSB
14 bit X Data R
XD13
XD12
02
OUT_X_LSB
14 bit X Data R
XD5
XD4
03
OUT_Y_MSB
14 bit Y Data R
YD13
YD12
04
OUT_Y_LSB
14 bit Y Data R
YD5
YD4
05
OUT_Z_MSB
14 bit Z Data R
ZD13
ZD12
06
OUT_Z_LSB
14 bit Z Data R
ZD5
ZD4
ZD3
ZD2
ZD1
ZD0
0
0
09
F_SETUP
FIFO Set-up R/W
F_MODE1
F_MODE0
F_WMRK5
F_WMRK4
F_WMRK3
F_WMRK2
F_WMRK1
F_WMRK0
0A
TRIG_CFG
FIFO Triggers R/W
—
—
Trig_TRANS
Trig_LNDPRT
Trig_PULSE
Trig_FF_MT
—
—
0B
SYSMOD
System Mode R
FGERR
FGT_4
FGT_3
FGT_2
FGT_1
FGT_0
SYSMOD1
SYSMOD0
0C
INT_SOURCE
Interrupt Status R
SRC_ASLP
SRC_FIFO
SRC_TRANS
SRC_LNDPRT
SRC_PULSE
SRC_FF_MT
—
SRC_DRDY
0D
WHO_AM_I
ID Register R
0
0
0
1
1
0
1
0
0E
XYZ_DATA_CFG
Data Config R/W
—
—
—
HPF_Out
—
—
FS1
FS0
0F
HP_FILTER_CUTOFF
HP Filter Setting R/W
—
—
Pulse_HPF_BYP
Pulse_LPF_EN
—
—
SEL1
SEL0
10
PL_STATUS
PL Status R
NEWLP
LO
—
—
—
LAPO[1]
LAPO[0]
BAFRO
11
PL_CFG
PL Configuration R/W
DBCNTM
PL_EN
—
—
—
—
—
—
12
PL_COUNT
PL DEBOUNCE R/W
DBNCE[7]
DBNCE[6]
DBNCE[5]
DBNCE[4]
DBNCE[3]
DBNCE[2]
DBNCE[1]
DBNCE[0]
13
PL_BF_ZCOMP
PL Back/Front Z Comp
R/W
BKFR[1]
BKFR[0]
—
—
—
ZLOCK[2]
ZLOCK[1]
ZLOCK[0]
14
P_L_THS_REG
PL THRESHOLD R/W
P_L_THS[4]
P_L_THS[3]
P_L_THS[2]
P_L_THS[1]
P_L_THS[0]
HYS[2]
HYS[1]
HYS[0]
15
FF_MT_CFG
Freefall/Motion Config
R/W
ELE
OAE
ZEFE
YEFE
XEFE
—
—
—
16
FF_MT_SRC
Freefall/Motion Source
R
EA
—
ZHE
ZHP
YHE
YHP
XHE
XHP
FF_MT_THS
Freefall/Motion Threshold
R/W
DBCNTM
THS6
THS5
THS4
THS3
THS2
THS1
THS0
17
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
YOW
XOW
ZYXDR
ZDR
YDR
XDR
XD11
XD10
XD9
XD8
XD7
XD6
XD3
XD2
XD1
XD0
0
0
YD11
YD10
YD9
YD8
YD7
YD6
YD3
YD2
YD1
YD0
0
0
ZD11
ZD10
ZD9
ZD8
ZD7
ZD6
18
FF_MT_COUNT
Freefall/Motion Debounce
R/W
D7
D6
D5
D4
D3
D2
D1
D0
1D
TRANSIENT_CFG
Transient Config R/W
—
—
—
ELE
ZTEFE
YTEFE
XTEFE
HPF_BYP
1E
TRANSIENT_SRC
Transient Source R
—
EA
ZTRANSE
Z_Trans_Pol
YTRANSE
Y_Trans_Pol
XTRANSE
X_Trans_Pol
1F
TRANSIENT_THS
Transient Threshold R/W
DBCNTM
THS6
THS5
THS4
THS3
THS2
THS1
THS0
20
TRANSIENT_COUNT
Transient Debounce
R/W
D7
D6
D5
D4
D3
D2
D1
D0
21
PULSE_CFG
Pulse Config R/W
DPA
ELE
ZDPEFE
ZSPEFE
YDPEFE
YSPEFE
XDPEFE
XSPEFE
22
PULSE_SRC
Pulse Source R
EA
AxZ
AxY
AxX
DPE
Pol_Z
Pol_Y
Pol_X
23
PULSE_THSX
Pulse X Threshold R/W
—
THSX6
THSX5
THSX4
THSX3
THSX2
THSX1
THSX0
24
PULSE_THSY
Pulse Y Threshold R/W
—
THSY6
THSY5
THSY4
THSY3
THSY2
THSY1
THSY0
25
PULSE_THSZ
Pulse Z Threshold R/W
—
THSZ6
THSZ5
THSZ4
THSZ3
THSZ2
THSZ1
THSZ0
26
PULSE_TMLT
Pulse First Timer R/W
TMLT7
TMLT6
TMLT5
TMLT4
TMLT3
TMLT2
TMLT1
TMLT0
27
PULSE_LTCY
Pulse Latency R/W
LTCY7
LTCY6
LTCY5
LTCY4
LTCY3
LTCY2
LTCY1
LTCY0
28
PULSE_WIND
Pulse 2nd Window
R/W
WIND7
WIND6
WIND5
WIND4
WIND3
WIND2
WIND1
WIND0
29
ASLP_COUNT
Auto-SLEEP Counter
R/W
D7
D6
D5
D4
D3
D2
D1
D0
2A
CTRL_REG1
Control Reg1 R/W
ASLP_RATE1
ASLP_RATE0
DR2
DR1
DR0
LNOISE
F_READ
ACTIVE
2B
CTRL_REG2
Control Reg2 R/W
ST
RST
—
SMODS1
SMODS0
SLPE
MODS1
MODS0
2C
CTRL_REG3
Control Reg3
(WAKE Interrupts from
SLEEP) R/W
FIFO_GATE
WAKE_TRANS
WAKE_LNDPRT
WAKE_PULSE
WAKE_FF_MT
—
IPOL
PP_OD
2D
CTRL_REG4
Control Reg4
(Interrupt Enable Map)
R/W
INT_EN_ASLP
INT_EN_FIFO
INT_EN_TRANS
INT_EN_LNDPRT
INT_EN_PULSE
INT_EN_FF_MT
—
INT_EN_DRDY
2E
CTRL_REG5
Control Reg5
(Interrupt Configuration)
R/W
INT_CFG_ASLP
INT_CFG_FIFO
INT_CFG_TRANS
INT_CFG_LNDPRT
INT_CFG_PULSE
INT_CFG_FF_MT
—
INT_CFG_DRDY
2F
OFF_X
X 8-bit offset R/W
D7
D6
D5
D4
D3
D2
D1
D0
30
OFF_Y
Y 8-bit offset R/W
D7
D6
D5
D4
D3
D2
D1
D0
31
OFF_Z
Z 8-bit offset R/W
D7
D6
D5
D4
D3
D2
D1
D0
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Table 74. Accelerometer Output Data
14-bit Data
Range ±2g (0.25 mg)
Range ±4g (0.5 mg)
Range ±8g (1.0 mg)
01 1111 1111 1111
1.99975g
+3.9995g
+7.999g
01 1111 1111 1110
1.99950g
+3.9990g
+7.998g
…
…
…
…
00 0000 0000 0001
0.00025g
+0.0005g
+0.001g
00 0000 0000 0000
0.00000g
0.00000g
0.000g
11 1111 1111 1111
-0.00025g
-0.0005g
-0.001g
…
…
…
…
10 0000 0000 0001
-1.99975g
-3.9995g
-7.999g
10 0000 0000 0000
-2.00000g
-4.0000g
-8.000g
8-bit Data
Range ±2g (15.6 mg)
Range ±4g (31.25 mg)
Range ±8g (62.5 mg)
0111 1111
1.9844g
+3.9688g
+7.9375g
0111 1110
1.9688g
+3.9375g
+7.8750g
…
…
…
…
0000 0001
+0.0156g
+0.0313g
+0.0625g
0000 0000
0.000g
0.0000g
0.0000g
1111 1111
-0.0156g
-0.0313g
-0.0625g
…
…
…
…
1000 0001
-1.9844g
-3.9688g
-7.9375g
1000 0000
-2.0000g
-4.0000g
-8.0000g
MMA8451Q
Sensors
Freescale Semiconductor
49
PACKAGE DIMENSIONS
CASE 2077-01
ISSUE O
16-LEAD QFN
MMA8451Q
50
Sensors
Freescale Semiconductor
PACKAGE DIMENSIONS
CASE 2077-01
ISSUE O
16-LEAD Q
MMA8451Q
Sensors
Freescale Semiconductor
51
PACKAGE DIMENSIONS
CASE 2077-01
ISSUE O
16-LEAD Q
MMA8451Q
52
Sensors
Freescale Semiconductor
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MMA8451Q
Rev. 3
09/2010