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相关参考资料

MMA8452Q.pdf 403KB

AN4073.pdf 307KB

AN4069.pdf 192KB

AN4077.pdf 238KB

AN4076SW.zip 493KB

AN4068.pdf 225KB

AN4070.pdf 316KB

AN4076.pdf 489KB

测试代码

51_MCU_GY-45_MMA8452

MMA8452_stc串口

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STARTUP.A51 5KB

MMA8452_串口.M51 21KB

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STARTUP.OBJ 749B

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MMA8452_串口 16KB

电路图

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电路图

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AN4076

Rev 0, 09/2010

Freescale Semiconductor

Application Note

Data Manipulation and Basic Settings of the

MMA8451, 2, 3Q

by:

Kimberly Tuck

Applications Engineer

1.0 Introduction

It is important to understand how to program the MMA8451,

2, 3Q to extract and manipulate the acceleration data. These

devices have been designed to be compatible with a shared

memory map. For details on the differences of the embedded

features please review our selector guide. The MMA8451Q

has the most embedded features which include eight different

sample rates, 32 different cut-off frequencies for the high pass

filter, 3 dynamic ranges and four oversampling modes. It also

has a 32 sample FIFO for collecting and storing data, which is

the most efficient way to access the data for minimizing the

C transactions. The FIFO can collect the regular low pass

filtered data as well as the data from the high pass filter. The

manipulation of the data into different formats is important for

algorithm development and for display. This application note

accompanies the MMA8451, 2, 3Q Driver Code and will

explain the following:

• Changing the operational modes (Standby, Active 2g,

Active 4g and Active 8g)

• Changing Oversampling Modes

• Changing the Data Rate

• Changing the High Pass Filter Cut-off Frequency

• 8-bit data vs. 14/12/10-bit data

• Changing Data Formats (hex to counts to decimal

numbers)

• Streaming XYZ data polling vs. Streaming XYZ data with

interrupts

• Using the FIFO in the MMA8451Q

1.1 Key Words

Accelerometer, Output Data Rate, Standby Mode, Active

Mode, High Pass Filter Cut-off Frequency, 8-bit Data, 14-bit

Data, 12-bit Data, 10-bit Data Hexadecimal Numbers,

Decimal Numbers, Data Formats, Streaming Data, Counts,

Polling, Interrupts, FIFO Data, Flush, Sensor Toolbox Demo

Board, Driver Code, High Pass Filtered Data, Low Pass

Filtered Data

TABLE OF CONTENTS

1.0 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.1 Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.0 MMA845xQ Consumer 3-axis Accelerometers 3 mm x 3 mm x 1 mm . . 2

2.1 Output Data, Sample Rates and Dynamic Ranges of all Three Products . . .3

2.1.1 MMA8451Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2.1.2 MMA8452Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2.1.3 MMA8453Q Note: No HPF Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

2.2 Application Notes for the MMA8451, 2, 3Q . . . . . . . . . . . . . . . . . . . . . . . . . . 3

3.0 Changing Modes of the MMA8451, 2, 3Q . . . . . . . . . . . . . . . . . . . . . . . . .4

3.1 Standby and Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.2 2g Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.3 4g Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.4 8g Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4.0 Setting the Data Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

5.0 Setting the Oversampling Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

6.0 Setting the High Pass Filter Cut-off Frequency . . . . . . . . . . . . . . . . . . . .9

6.1 High Pass Filtered Data or Low Pass Filtered Data . . . . . . . . . . . . . . . . . . . 10

7.0 14-bit, 12-bit or 10-bit Data Streaming and Data Conversions. . . . . . . . 10

7.1 Converting 14-bit 2’s Complement Hex Number to Signed Integer (Counts)

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7.2 Converting 14-bit 2’s Complement Hex Number to Signed Decimal Fraction in

g’s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7.2.1 2g Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7.2.2 4g Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7.2.3 8g Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

8.0 8-bit XYZ Data Streaming and Conversions . . . . . . . . . . . . . . . . . . . . . .17

8.1 Converting 8-bit 2’s Complement Hex Number to Signed Integer Number . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

8.2 Converting 8-bit 2’s Complement Hex Number to Signed Decimal Fraction in

g’s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8.2.1 2g Active Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

9.0 Polling Data vs. Interrupts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

9.1 Polling Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

9.2 Interrupt Routine to Access Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

10.0 Using the 32 Sample FIFO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

11.0 MMA845xQ Driver Code. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

AN4076

Sensors

2 Freescale Semiconductor

1.2 Summary

A. There is a Standby Mode which responds to I

C communication but doesn’t allow for updated data. There are also

3 dynamic ranges: 2g, 4g and 8g which can be used to observe the change in sensitivity and full acceleration range

while the device is active.

B. An example of how to set the data rate is shown. There are 8 different data rates ranging from 1.56 Hz to 800 Hz.

C. An example of how to set the High Pass Filter Cut-off Frequency is given. The high pass filtered output data is

affected by the filter cut-off frequency settings.

D. There are 4 different oversampling modes that can be set.

E. An example and the format conversions for manipulating 14/12/10/8-bit data converting 2’s complement hex data

to two different formats, which include formatting to signed integer (counts) and signed decimal fractions in g’s for

high pass filtered data or low pass filtered data.

F. An example of how to set up the device to poll the data or configure an interrupt service routine is shown.

G. An example of how to configure the FIFO to store and flush data.

H. There is a driver available that will run on the MMA8451, 2, 3Q Sensor Toolbox Demo Board that provides an

example in CodeWarrior for everything discussed in the application note. The driver runs in RealTerm or

HyperTerminal and can be used to capture and log data in different formats.

2.0 MMA845xQ Consumer 3-axis Accelerometers 3 mm x 3 mm x 1 mm

The MMA8451, 2, 3Q has a selectable dynamic range of ±2g, ±4g, ±8g. The device has 8 different output data rates, selectable

high pass filter cut-off frequencies, and in some cases high pass filtered output data available. The resolution of the data and the

embedded features is dependant on the specific device.

Note: The MMA8451, 2, 3Q has a different memory map than that of the MMA8450Q.

Figure 1. MMA8451, 2, 3Q Consumer 3-axis Accelerometer 3 mm x 3 mm x 1 mm

GND

VDDIO

SCL

INT2

INT1

GND

SDA

SA0

VDD

BYP

MMA845xQ

16 Pin QFN

3mmx3mmx1mm

(Top View)

1415

AN4076

Sensors

Freescale Semiconductor 3

2.1 Output Data, Sample Rates and Dynamic Ranges of all Three Products

2.1.1 MMA8451Q

1. 14-bit data

2g (4096 counts/g = 0.25 mg/LSB) 4g (2048 counts/g = 0.5 mg/LSB) 8g (1024 counts/g = 1 mg/LSB)

2. 8-bit data

2g (64 counts/g = 15.6 mg/LSB) 4g (32 counts/g = 31.25 mg/LSB) 8g (16 counts/g = 62.5 mg/LSB)

3. Embedded 32 sample FIFO (MMA8451Q)

2.1.2 MMA8452Q

1. 12-bit data

2g (1024 counts/g = 1 mg/LSB) 4g (512 counts/g = 2 mg /LSB) 8g (256 counts/g = 3.9 mg/LSB)

2. 8-bit data

2g (64 counts/g = 15.6 mg/LSB) 4g (32 counts/g = 31.25 mg/LSB) 8g (16 counts/g = 62.5 mg/LSB)

2.1.3 MMA8453Q Note: No HPF Data

1. 10-bit data

2g (256 counts/g = 3.9 mg/LSB) 4g (128 counts/g = 7.8 mg/LSB) 8g (64 counts/g= 15.6 mg/LSB)

2. 8-bit data

2g (64 counts/g = 15.6 mg/LSB) 4g (32 counts/g = 31.25 mg/LSB) 8g (16 counts/g = 62.5 mg/LSB)

2.2 Application Notes for the MMA8451, 2, 3Q

The following is a list of all the application notes available 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

AN4076

Sensors

4 Freescale Semiconductor

3.0 Changing Modes of the MMA8451, 2, 3Q

The device can be in either Standby Mode or Active Mode. Most of the settings are changed in Standby Mode but the data

does not update and is not enabled until the device is in Active Mode. There are also 3 different dynamic ranges that can be set

(2g, 4g, 8g). The dynamic range is changeable only in the Standby Mode. The dynamic range is controlled by setting the FS0

and FS1 bits in register 0x0E. The device changes from Standby to Active Mode via bit 0 in register 0x2A.

3.1 Standby and Active Mode

Most, although not quite all changes to the registers must be done while the accelerometer is in Standby Mode. Current con-

sumption in Standby Mode is typically 1 - 2 μA. To be in Standby Mode the last bit of CTRL_REG1 must be cleared (Active = 0).

When Active = 1 the device is in the active mode.

Code Example:

void MMA845x_Standby (void)

{

byte n;

** Read current value of System Control 1 Register.

** Put sensor into Standby Mode by clearing the Active bit

** Return with previous value of System Control 1 Register.

n = IIC_RegRead(CTRL_REG1);

IIC_RegWrite(CTRL_REG1, n & ~ACTIVE_MASK);

}

void MMA845x_Active ()

{

** Set the Active bit in CTRL Reg 1

IIC_RegWrite(CTRL_REG1, (IIC_RegRead(CTRL_REG1) | ACTIVE_MASK));

}

Table 1. 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 FREAD ACTIVE

Table 2. 0x0E XYZ_DATA_CFG Register (Read/Write)

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

—00 0HPF_Out0 0FS1 FS0

Table 3. Full Scale Selection

FS1 FS0 g Range

0 0 ±2g

0 1 ±4g

1 0 ±8g

11—

AN4076

Sensors

Freescale Semiconductor 5

3.2 2g Active Mode

In order to enter 2g Active Mode, the MMA8451, 2, 3Q must first be put into Standby Mode prior to changing the FS bits to 00

(as per Table 3).

Code Example:

**Put the part in Standby Mode

MMA845x_Standby();

**Write the 2g dynamic range value into register 0x0E

IIC_RegWrite(XYZ_DATA_CFG_REG, (IIC_RegRead(XYZ_DATA_CFG_REG) & ~FS_MASK));

**Put the part back into the Active Mode

MMA845x_Active();

3.3 4g Active Mode

In order to enter 4g Active Mode, the MMA8451, 2, 3Q must first be put into Standby Mode prior to changing the FS bits 01

(as per Table 3).

Code Example:

**Put the part in Standby Mode

MMA845x_Standby();

**Write the 4g dynamic range value into register 0x0E

IIC_RegWrite(XYZ_DATA_CFG_REG, (IIC_RegRead(XYZ_DATA_CFG_REG) & ~FS_MASK));

IIC_RegWrite(XYZ_DATA_CFG_REG, (IIC_RegRead(XYZ_DATA_CFG_REG) | FULL_SCALE_4G));

**Put the part back into the Active Mode

MMA845x_Active();

3.4 8g Active Mode

In order to enter 8g Active Mode, the MMA8451, 2, 3Q must first be put into Standby Mode prior to changing the FS bits to 10

(as per Table 3).

Code Example:

**Put the part in Standby Mode

MMA845x_Standby();

**Write the 8g dynamic range value into register 0x0E

IIC_RegWrite(XYZ_DATA_CFG_REG, (IIC_RegRead(XYZ_DATA_CFG_REG) & ~FS_MASK));

IIC_RegWrite(XYZ_DATA_CFG_REG, (IIC_RegRead(XYZ_DATA_CFG_REG) | FULL_SCALE_8G));

**Put the part back into the Active Mode

MMA845x_Active();

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