AN4519, Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code - Application Notes

Freescale Semiconductor
Application Note
Document Number: AN4519
Rev 0.1, 08/2012
Data Manipulation and
Basic Settings of the
MPL3115A2 Command Line
Interface Driver Code
by: Miguel Salhuana
1
Introduction
It is important to understand how to program the
MPL3115A2 to extract pressure and temperature data.
The MPL3115A2 has many different features which
include 8 different sample rates, 16 different acquisition
time steps (1 second to 9 hours), compensated direct
reading of Pressure (20 bit in Pascals) or Altitude (20 bit
in meters), compensated direct reading of temperature
(12 bit in degrees Celsius) and programmable events. It
also contains a 32-sample FIFO for collecting and
storing data, which gives it the ability to log data for up
to 12 days. The FIFO is the most efficient means of
accessing the data since it minimizes I2C transactions.
This application note accompanies the MPL3115A2
Command Line Interface Driver Code and will explain
how to change the following:
• Modes of operation: Standby, Active Altitude,
and Active Barometer
• Sample Rate (OSR)
• Data Acquisition Rate (ST)
• Data Formats (hex to decimal)
• Streaming Pressure/Altitude and Temperature
(PT) data polling versus Streaming PT Data with
interrupts
© 2012 Freescale Semiconductor, Inc. All rights reserved.
Contents
1
2
3
4
5
6
7
8
9
10
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
MPL3115A2 I2C Precision Altimeter . . . . . . . . . . . . . . . . 3
Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Setting the Data Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Data Streaming and Data Conversions . . . . . . . . . . . . . . 8
Polling Data Versus Interrupts. . . . . . . . . . . . . . . . . . . . 16
Pressure/Altitude Alarms Interrupts. . . . . . . . . . . . . . . . 19
Temperature Alarm Interrupts . . . . . . . . . . . . . . . . . . . . 24
Using the 32-sample FIFO . . . . . . . . . . . . . . . . . . . . . . 28
Command Line Interface User Guide . . . . . . . . . . . . . . 34
•
•
•
1.1
Using the FIFO to collect PT data by using Overflow and Watermark modes.
Altitude/Pressure Threshold Alarm and Window Alarm via interrupts
Temperature Threshold Alarm and Window Alarm via interrupts
Key words
Standby Mode, Active Mode, Altimeter Mode, Barometer Mode, Hexadecimal Numbers, Decimal
Numbers, Data Formats, Streaming Data, Polling, Interrupts, FIFO Data, Sensor Toolbox Demo Board,
Driver Code, Pressure
1.2
•
•
•
•
•
•
•
Summary
There are three modes: Standby Mode, Active Altimeter Mode and Active Barometer Mode.
An example of how to set the data rate (OSR) and the time step (ST) is shown. There are eight
OSRs and the time step can be set from 1 second to 9 hours in steps of powers of two.
Examples of how to setup the sensor to poll data or use an Interrupt Service Routine (ISR) to
retrieve data.
Use of the FIFO in either Overflow or Watermark mode.
Setup the programmable alarms for Pressure/Altitude with and without specifying a window.
Setup the programmable alarms for Temperature with and without specifying a window.
Read and write registers.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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MPL3115A2 I2C Precision Altimeter
2
The MPL3115A2 employs a MEMS pressure sensor with an I2C interface to provide accurate Pressure or
Altitude data. The sensor’s Pressure/Altitude and Temperature outputs are digitized by a high resolution
24-bit ADC. Internal processing removes the compensation tasks from the host MCU system.
VDD
1
8
SCL
CAP
2
7
SDA
GND
3
6
INT1
VDDIO
4
5
INT2
LGA Package
5.0 mm by 3.0 mm by 1.1 mm
Top View
Figure 1. Package and pinout diagram
2.1
•
•
•
•
•
•
•
•
•
•
2.2
•
•
•
•
•
•
•
•
Key features
1.95V to 3.6V Supply voltage
1.6V to 3.6V Digital interface supply voltage
Fully compensated internally
Direct reading, compensated
— Pressure: 20-bit measurement (Pascals)
— Altitude: 20-bit measurement (meters)
— Temperature: 12-bit measurement (degrees Celsius)
Programmable events
Autonomous data acquisition
Resolution down to 1 foot /30 cm
32-sample FIFO
Ability to log data up to 12 days using the FIFO
I2C digital output interface (operates up to 400 kHz)
Two programmable interrupt pins for eight interrupt sources
Data ready interrupt
Embedded 32-sample FIFO interrupt
Pressure/Altitude window alarm interrupt
Temperature window alarm interrupt
Pressure/Altitude threshold alarm interrupt
Temperature threshold alarm interrupt
Pressure change interrupt
Temperature change interrupt
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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3
3
Modes of Operation
The MPL3115A2 has three modes: Standby, Active Altimeter and Active Barometer. The Standby/Active
modes are controlled by bit 0 of the System Control Register (CTRL_REG_1), named SBYB. To switch
between the Altimeter and Barometer functionality, flip the ALT bit of CTRL_REG_1.
CTRL_REG_1
7
6
5
4
3
ALT
RAW
OS2
OS1
OS0
R
2
1
0
OST
SBYB
0
0
0
W
RST
Reset
0
0
0
0
0
0
Figure 2. System Control Register 1
3.1
Standby mode
The MPL3115A2 goes into standby mode when a 0 is written to the Standby-Bar, SBYB (bit 0) of
CTRL_REG_1. All register writes must be done with the part in Standby mode. The SBYB bit can be
written to in Active mode to put the part into Standby mode.
Example 1.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
3.2
Active Altimeter mode
In order to enter Altimeter Active mode, the MPL3115A2 must be put into standby mode prior to any
changes. You must then write a 1 to the ALT bit of CTRL_REG_1 and a 1 to SBYB bit to go into active
mode. These writes to the ALT and SBYB can be done in a single I2C transaction.
Example 2.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Write a 1 to the ALT and SBYB bits to go into Active Altimeter mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | ALT _MASK |
ACTIVE_MASK));
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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NOTE
In Altimeter mode, the 20-bit value stored in OUT_P_MSB, OUT_P_CSB
and OUT_P_LSB is in meters represented as a signed 16-bit value in
OUT_P_MSB and OUT_P_CSB and unsigned fractional value in bits 7-4
of OUT_P_LSB. Bits 3-0 of OUT_P_LSB are unused in this mode.
3.3
Active Barometer mode
In order to enter Active Barometer mode, the MPL3115A2 must be put into Standby mode prior to any
changes. You must then write a 0 to the ALT bit of CTRL_REG_1 and a 1 to SBYB bit to go into Active
mode.
Example 3.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Write a 0 to the ALT and a 1 SBYB bits to go into Active Barometer mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | BAR_MASK | ACTIVE_MASK));
NOTE
In Barometer mode, the 20-bit value stored in OUT_P_MSB, OUT_P_CSB
and OUT_P_LSB is in Pascals represented as an unsigned 18-bit value in
OUT_P_MSB, OUT_P_CSB and bits 7-6 of OUT_P_LSB with the
fractional value in bits 5-4 of OUT_P_LSB. Bits 3-0 of OUT_P_LSB are
unused in this mode.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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4
Setting the Data Rate
4.1
Setting the Output Sample Rate (OSR)
The OSR is programmable via the OS[2:0] in CTRL_REG1 see Figure 3.
CTRL_REG_1
7
6
5
4
3
ALT
RAW
OS2
OS1
OS0
R
2
1
0
OST
SBYB
0
0
0
W
RST
Reset
0
0
0
0
0
0
Figure 3. System Control Register 1
Example 4.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/**
** The OSR_Value is set to 0 - 7 corresponding with Ratios 1 - 128
*/
if (OSR_Value < 8) {
OSR_Value <<= 3;
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA |OSR_Value));
}
4.2
Setting the Time Step (ST)
The Auto Acquisition Time Step is programmable via the ST[2:0] control bits in the CTRL_REG_2
illustrated in Figure 4 and Table 1.
CTRL_REG_2
R
7
6
0
0
5
4
3
2
1
0
LOAD_OUTPUT
ALARM_SEL
ST[3]
ST[2]
ST[1]
ST[0]
0
0
0
0
0
0
W
Reset
0
0
Figure 4. System Control Register 2
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Table 1. Auto Acquisition Time Step
ST[3]
ST[2]
ST[1]
ST[0]
Time Step
(seconds)
0
0
0
0
1
0
0
0
1
2
0
0
1
0
4
0
0
1
1
8
0
1
0
0
16
0
1
0
1
32
0
1
1
0
64
0
1
1
1
128
1
0
0
0
256
1
0
0
1
512
1
0
1
0
1024
1
0
1
1
2048
1
1
0
0
4096
1
1
0
1
8192
1
1
1
0
16384
1
1
1
1
32768
Example 5.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/**
** The ST_Value is set from 0x1 - 0xF corresponding steps 1 - 32,768
*/
if (ST_Value <= 0xF) {
CTRL_REG_2_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG2);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG2, (CTRL_REG_2_DATA|ST_Value));
}
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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5
Data Streaming and Data Conversions
The MPL3115A2 can provide 20-bit pressure data in meters or Pascals. This section is an overview of how
to manipulate that data to continuously stream out this 20-bit data. The pressure/temperature data
configuration register, PT_DATA_CFG (0x13), has control bits used to enable the internal event flag upon
detection of new data, which would occur at the selected OSR. At least one of the data ready enable bits
(DREM, PDEFE or TDEFE shown in Figure 4) must be set to active so that an event flag will occur when
an updated sample is ready.
PT_DATA_CFG
7
6
5
4
3
2
1
0
DREM
PDEFE
TDEFE
0
0
0
R
W
Reset
0
0
0
0
0
Figure 5. Pressure Data Configuration
The following line of code illustrates how to set the event flag to be generated when a new pressure/altitude
reading is available to be read:
IIC_RegWrite(SlaveAddressIIC, PT_DATA_CFG_REG, PDEFE_MASK );
Once configured, the event flag can be monitored by reading the STATUS register at address 0x00/0x06.
This can be done by using either a polling or interrupt technique, which is discussed later in Section 6,
“Polling Data Versus Interrupts” of this document. Regardless of the technique used, the STATUS register
needs to be read and the appropriate flag monitored.
DR_STATUS
R
7
6
5
4
3
2
1
0
PTOW
POW
TOW
0
PTDR
PDR
TDR
0
0
0
0
0
0
0
0
0
W
Reset
Figure 6. Pressure Data Status
The PDR flag is set whenever there is new pressure data available. The following code example monitors
this flag and upon detection of new data, reads the 20-bit Pressure data into three separate 8-bit variables
for further processing.
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Example 6.
RegisterFlag.Byte = IIC_RegRead(SlaveAddressIIC, DR_STATUS_00_REG);
if (RegisterFlag.PDR_BIT == 1)
{
/*
** Read 20 bit Pressure Data Results
** and store in 8 bit registers
*/
pressure_value_raw.Byte.tp_msb = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
pressure_value_raw.Byte.tp_csb = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
pressure_value_raw.Byte.tp_lsb = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
}
NOTE
In RAW mode the pressure value is stored in all 24 bits that comprise
OUT_P_MSB, OUT_P_CSB and OUT_P_LSB; and for the temperature
value all 16 bits of OUT_T_MSB and OUT_T_LSB are utilized.
5.1
Converting a 20-bit Altitude reading to a signed decimal number
The 20-bit measurement in meters is comprised of a signed integer component and a fractional component.
The signed 16-bit integer component located in OUT_P_MSB and OUT_P_CSB. The fraction component
is located in bits 7-4 of OUT_P_LSB. Bits 3-0 of OUT_P_LSB are not used.
The sign of the result is easy to determine by simply checking if the high byte of the value is greater than
0x7F. If so, then the value is a negative number and needs to be transformed by performing a 2’s
complement conversion. This involves executing a 1’s complement (i.e., switch all 1’s to 0’s and all 0’s to
1’s) and followed by adding 1 to the result. The following code outputs the data in this format:
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Example 7.
void SCI_s16dec_Out (tword data)
{
byte a, b, c, d;
word r;
/*
** Determine sign and output
*/
if (data.Byte.hi > 0x7F)
{
SCI_CharOut ('-');
data.Word = ~data.Word + 1;
}
else
{
SCI_CharOut ('+');
}
/*
** Calculate
*/
a = (byte)((data.Word) / 1000);
r = (data.Word) % 1000;
b = (byte)(r / 100);
r %= 100;
c = (byte)(r / 10);
d = (byte)(r % 10);
/*
** Format
*/
if (a == 0)
{
a = 0xF0;
if (b == 0)
{
b = 0xF0;
if (c == 0)
{
c = 0xF0;
}
}
}
/*
** Output result
** The SCI_NibbOut function outputs a SCI single hex nibble character
*/
SCI_NibbOut (a);
SCI_NibbOut (b);
SCI_NibbOut (c);
SCI_NibbOut (d);
}
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To convert the fractional component in OUT_P_LSB, we use the upper byte of the value. Since the
resolution is in 0.0625 meters, we can compute the fractional value by using the following table.
Table 2. Fraction Computation
Bit 7
Bit 6
Bit 5
Bit 4
Assigned Value
1
0
0
0
0.5
0
1
0
0
0.25
0
0
1
0
0.125
0
0
0
1
0.0625
We can then add these values together for each bit that is a 1 and we get the fractional component of the
altitude value in fractions of a meter. For example, the value of 0.75 meters will be represented by the
following 4-bit value: 1100. So using the table above, you would add 0.5 to 0.25 to get 0.75 meters.
Example 8.
void SCI_s4fracun_Out (tword data)
{
BIT_FIELD value;
word result;
byte a, b, c, d;
word r;
SCI_CharOut ('.');
/*
** Determine mantissa value
*/
result = 0;
value.Byte = data.Byte.hi;
if (value.Bit._7 == 1)
result += FRAC_2d1;
if (value.Bit._6 == 1)
result += FRAC_2d2;
if (value.Bit._5 == 1)
result += FRAC_2d3;
if (value.Bit._4 == 1)
result += FRAC_2d4;
//
/*
** Convert mantissa value to 4 decimal places
*/
r = result % 1000;
a = (byte)(result / 1000);
b = (byte)(r / 100);
r %= 100;
c = (byte)(r / 10);
d = (byte)(r % 10);
/*
** Output mantissa
*/
SCI_NibbOut (a);
SCI_NibbOut (b);
SCI_NibbOut (c);
SCI_NibbOut (d);
}
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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5.2
Converting a 20-bit barometric pressure reading to a decimal
value
The 20-bit measurement in Pascals is comprised of an unsigned integer component and a fractional
component. The unsigned 18-bit integer component is located in OUT_P_MSB, OUT_P_CSB and bits 7-6
of OUT_P_LSB. The fractional component is located in bits 5-4 of OUT_P_LSB. Bits 3-0 of
OUT_P_LSB are not used.
In order to compute the decimal value of the pressure the 20-bit value contained in OUT_P_MSB,
OUT_P_CSB and OUT_P_LSB is shifted to the right six places. We can then compute the 18-bit
hexadecimal value to an unsigned decimal. The following code achieves this:
Example 9.
void SCI_s18decun_Out (tbar_18 data)
{
byte a, b, c, d, e, f, g, h;
dword r;
/*
** Calculate
*/
a = (byte)((data.LWord>>6) / 10000000);
//shift by 6
r = (data.LWord>>6) % 10000000;
b = (byte)(r / 1000000);
r %= 1000000;
c = (byte)(r / 100000);
r %= 100000;
d = (byte)(r / 10000);
r %= 10000;
e = (byte)(r / 1000);
r %= 1000;
f = (byte)(r / 100);
r %= 100;
g = (byte)(r / 10);
h = (byte)(r % 10);
/*
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** Format
*/
if (a == 0)
{
a = 0xF0;
if (b == 0)
{
b = 0xF0;
if (c == 0)
{
c = 0xF0;
if (d == 0) {
d = 0xF0;
if (e==0){
e = 0xF0;
if (f == 0){
f = 0xF0;
if ( g == 0 ) {
g = 0xF0;
}
}
}
}
}
}
}
/*
** Output result
*/
SCI_NibbOut (d);
SCI_NibbOut (e);
SCI_NibbOut (f);
SCI_NibbOut (g);
SCI_NibbOut (h);
}
To convert the fractional component contained in bits 5-4 of OUT_P_LSB we use the upper byte of the
value and shift it to the left by two places. The resolution is in 0.25 Pascals we can compute the fractional
value by using the following table:
Table 3. Fraction Computation
Bit 5
Bit 4
Assigned Value
0
1
0.5
1
0
0.25
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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We can then add these values together for each bit that is a 1 and we get the fractional component of the
altitude value in meters. So for a value of 0.75 bit 5 and bit 4 will both be set to 1 which will give you 0.5
+ 0.25 = 0.75.
Example 10.
void SCI_s2fracun_Out (tword data)
{
BIT_FIELD value;
word result;
byte a, b, c, d;
word r;
SCI_CharOut ('.');
/*
** Determine mantissa value
*/
result = 0;
value.Byte = data.Byte.hi;
if (value.Bit._5 == 1)
result += FRAC_2d1;
if (value.Bit._4 == 1)
result += FRAC_2d2;
/*
** Convert mantissa value to 2 decimal places
*/
r = result % 1000;
a = (byte)(result / 1000);
b = (byte)(r / 100);
r %= 100;
c = (byte)(r / 10);
d = (byte)(r % 10);
/*
** Output mantissa
*/
SCI_NibbOut (a);
SCI_NibbOut (b);
}
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5.3
Converting a 16-bit temperature reading to a signed decimal
number
The 12-bit temperature measurement in degrees Celsius is comprised of a signed integer component and
a fractional component. The signed 8-bit integer component is located in OUT_T_MSB. The fractional
component is located in bits 7-4 of OUT_T_LSB. Bits 3-0 of OUT_T_LSB are not used.
The sign of the result is easy to determine by simply checking if the high byte of the value is greater than
0x7F. If so, then the value is a negative number and needs to be transformed by performing a 2’s
complement conversion. This involves executing a 1’s complement (i.e., switch all 1’s to 0’s and all 0’s to
1’s) and followed by adding 1 to the result. The following code outputs the data in this format:
Example 11.
void SCI_s8dec_Out (tword data)
{
byte a, b, c;
word r;
/*
** Determine sign and output
*/
if (data.Byte.hi > 0x7F)
{
SCI_CharOut ('-');
data.Word = ~data.Word + 1;
}
else
{
SCI_CharOut ('+');
}
/*
** Calculate
*/
a = (byte)((data.Word >>8) / 100); //Shift the data over since it is MSB only
r = (data.Word >>8) % 100;
b = (byte)(r / 10);
c = (byte)(r % 10);
/*
** Format
*/
if (a == 0)
{
a = 0xF0;
if (b == 0)
{
b = 0xF0;
}
}
/*
** Output result
*/
SCI_NibbOut (a);
SCI_NibbOut (b);
SCI_NibbOut (c);
}
The conversion of the fractional component is done using the same methodology as in converting fractions
of a meter illustrated in Section 5.1, “Converting a 20-bit Altitude reading to a signed decimal number”.
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6
Polling Data Versus Interrupts
The data can be polled continuously or a hardware interrupt can be configured to signal when the data
ready flag is set. The MCU can then use an interrupt service routine to retrieve the data. Depending on the
circumstances, one might be more desirable than the other although polling typically is less efficient.
6.1
Polling data
Polling requires less configuration of the device and is very simple to implement. However, the MCU must
poll the sensor at a rate that is faster than the output data rate. Otherwise, if the polling is too slow, data
samples will be missed. The MCU can detect the missed or corrupted data condition by checking the
overwrite flags in the STATUS register (i.e., PTOW, POW, TOW, PTDR, PDR, and TDR). The code
examples provided so far in this document have primarily described the polling technique. As a summary,
here is a more complete example of the basic code, specific to the operation of the MPL3115A2, required
to continuously poll 20-bit PT data using the Altimeter Active mode:
Example 12.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Write a 1 to the ALT and SBYB bits to go into Active Altimeter mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | ALT _MASK |
ACTIVE_MASK));
/*
** Using a basic control loop, continously poll the sensor
*/
for (;;) {
/**
** Poll the
*/
RegisterFlag.Byte = IIC_RegRead(SlaveAddressIIC, DR_STATUS_00_REG);
if (RegisterFlag.PDR_BIT == 1)
if (RegisterFlag.TDR_BIT == 1) {
SCISendString(" Hex ");
temp =
IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
a_mcsb_value.Byte.hi = temp;
SCI_ByteOut(temp);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
a_mcsb_value.Byte.lo = temp;
SCI_ByteOut(temp);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
a_dec_value.Byte.lo = 0x0;
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
16
Freescale Semiconductor, Inc.
a_dec_value.Byte.hi = temp;
SCI_ByteOut(temp);
SCISendString(" Dec ");
SCI_s16dec_Out(a_mcsb_value);
SCI_s4fracun_Out(a_dec_value);
SCISendString(" Hex ");
temp =
IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
SCI_ByteOut(temp);
t_msb_value.Byte.hi = temp;
t_msb_value.Byte.lo = 0x0;
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
t_lsb_value.Byte.hi = temp;
t_lsb_value.Byte.lo = 0x0;
SCI_ByteOut(temp);
SCISendString(" Dec ");
SCI_s8dec_Out(t_msb_value);
SCI_s4fracun_Out(t_lsb_value);
}
}
}
6.2
Interrupt routine to access data
Streaming data via hardware interrupts is more efficient than polling as the MCU only interfaces with the
MPL3115A2 when it has new data. The output registers are read only when new data is available. If the
data is not read every time, the acquisition of new data will be indicated by the overwrite register flags.
The following are the register settings to configure the MPL3115A2 to generate an interrupt upon each
new Pressure and Temperature (PT) sample in Altimeter mode. The MCU’s Interrupt Service Routine
(ISR) shown below responds by reading the 20-bit Pressure and 12-bit Temperature data and setting a
software flag indicating the arrival of new data. It is considered to be good practice to keep ISRs as fast as
possible, so the actual processing of this data is not done here.
Please be aware that when enabling/disabling interrupts you should clear all existing interrupts.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
17
Example 13.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_DRDY_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_DRDY_MASK);
/*
** Configure the INT pins for Open Drain and Active Low.
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG3, (PP_OD1_MASK | PP_OD2_MASK));
/*
** Write a 1 to the ALT and SBYB bits to go into Active Altimeter mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | ALT _MASK |
ACTIVE_MASK));
interrupt void isr_MPL3115A2 (void)
{
/*
** Clear the interrupt flag
*/
CLEAR_MPL3115A2_INTERRUPT;
/** setting CHECK_INT flag to true
** allows us to handle the data manipulation
** in the main loop
*/
CHECK_INT = TRUE;
}
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Freescale Semiconductor, Inc.
7
Pressure/Altitude Alarms Interrupts
The MPL3115A2 provides two Pressure/Altitude alarm interrupts, a threshold alarm and a window alarm.
For the Threshold alarm the interrupt flag is set on reaching the value stored in the Pressure/Altitude target
register (P_TGT). Additionally, a window value (P_WND) provides the ability to signal when the target is
nearing the lower and upper threshold values set as offsets from the Pressure/Altitude target value. When
in barometer mode, these values represent pressures rather than altitudes.
Examples:
• Set Altitude alert to 3000m and window value to 100m, interrupt is asserted passing 2900m,
3000m, and 3100m.
• Set Pressure alert to 100.0 kPa and window value to 5 kPa, interrupt is asserted passing 95 kPa,
100 kPa and 105 kPa.
The Window alarm interrupt flag is set when the temperature value is within the window defined by the
following equation:
Window = P_TGT MSB ,LSB  P_WND MSB ,LSB
7.1
Eqn. 1
Altitude alarms
In Altitude mode the target value in P_TGT_(MSB,LSB) is a signed 16-bit 2's complement value in meters.
The window value in P_WND(MSB,LSB) is an unsigned 16-bit value in meters.
7.1.1
Setting threshold alarm for target Altitude
To set the altitude alarm so that the interrupt goes off only at the target altitude, we must set the
P_TGT_MSB and P_TGT_LSB registers to our target (in meters) and set the window register
P_WND_MSB and P_WND_LSB to zero. We then enable the Pressure threshold interrupt by writing a 1
to bit 3 (INT_EN_PTH) of CTRL_REG4 (Interrupt Enable register) and routing the interrupt to pin INT2
by writing a zero to bit 3 (INT_CFG_PTH) of CTRL_REG5 (Interrupt Configuration register).
CTRL_REG4
7
6
5
4
3
2
1
0
INT_EN_DRDY
INT_EN_FIFO
INT_EN_PW
INTE_EN_TW
INT_EN_PTH
INT_EN_TTH
INT_EN_PCHG
INT_EN_TCHG
0
0
0
0
0
0
0
0
R
W
Reset
Figure 7. Control Register 4
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
19
CTRL_REG5
(0x2A)
7
6
5
4
3
2
1
0
INT_CFG_DRDY
INT_CFG_FIFO
INT_CFG_PW
INTE_CFG_TW
INT_CFG_PTH
INT_CFG_TTH
INT_CFG_PCHG
INT_CFG_TCHG
0
0
0
0
0
0
0
0
R
W
Reset
Figure 8. Control Register 5
Example 14.
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
/*
** Write Target and Window Values
** value[3] and value[4] are set to 0
*/
IIC_RegWrite(SlaveAddressIIC, P_TGT_MSB, value[1]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_LSB, value[2]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_WND_MSB, value[3]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_WND_LSB, value[4]);
/*
** Enable Interrupt and Map to Interrupt Pin
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_PTH_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_PTH_MASK);
/*
** Write a 1 to the ALT and SBYB bits to go into Active Altimeter mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1,(CTRL_REG_1_DATA | ALT_MASK | ACTIVE MASK));
interrupt void isr_MPL3115A2 (void)
{
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Freescale Semiconductor, Inc.
/*
** Clear the interrupt flag
*/
CLEAR_MPL3115A2_INTERRUPT;
/** setting CHECK_INT flag to true
** allows us to handle the data interrupt
** in the main loop
*/
CHECK_INT = TRUE;
}
7.1.2
Setting Threshold Alarm for upper and lower thresholds
To set the Altitude alarm so that the interrupt goes off at the target altitude as well as at the lower and upper
thresholds, we must set the P_TGT_MSB and P_TGT_LSB registers to our target in meters and set the
window register P_WND_MSB and P_WND_LSB to the desired offset. We then enable the Pressure
threshold interrupt by writing a 1 to bit 3 (INT_EN_PTH) of CTRL_REG4 (Interrupt Enable register) and
routing the interrupt to pin INT2 by writing a zero to bit 3 (INT_CFG_PTH) of CTRL_REG5 (Interrupt
Configuration register).
Example 15.
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
/*
** Write Target and Window Values
** value[3] and value[4] are set to the offset
*/
IIC_RegWrite(SlaveAddressIIC, P_TGT_MSB, value[1]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_LSB, value[2]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_WND_MSB, value[3]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_WND_LSB, value[4]);
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
21
/*
** Enable Interrupt and Map to Interrupt Pin
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_PTH_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_PTH_MASK);
/*
** Write a 1 to the ALT and SBYB bits to go into Active Altimeter mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | ALT_MASK | ACTIVE MASK));
interrupt void isr_KBI (void)
{
/*
** Clear the interrupt flag
*/
CLEAR_KBI_INTERRUPT;
/** setting CHECK_INT flag to true
** allows us to handle the data interrupt
** in the main loop
*/
CHECK_INT = TRUE;
}
7.1.3
Setting the window alarm
To set the Altitude alarm so that the interrupt goes off only when we are in the window defined by P_TGT±
P_WND we must set the P_TGT_MSB and P_TGT_LSB registers to our target in meters and set the
window register P_WND_MSB and P_WND_LSB the desired offset. We then enable the Pressure
window interrupt by writing a 1 to bit 5 (INT_EN_PW) of CTRL_REG4 (Interrupt Enable register) and
routing the interrupt to pin INT2 by writing a zero to bit 5 (INT_CFG_PW) of CTRL_REG5 (Interrupt
Configuration register).
Example 16.
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Freescale Semiconductor, Inc.
/*
** Write Target and Window Values
** value[3] and value[4] are set to the offset
*/
IIC_RegWrite(SlaveAddressIIC, P_TGT_MSB, value[1]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_LSB, value[2]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_WND_MSB, value[3]);
IIC_RegWrite(SlaveAddressIIC, P_TGT_WND_LSB, value[4]);
/*
** Enable Interrupt and Map to Interrupt Pin
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_PW_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_PW_MASK);
/*
** Write a 1 to the ALT and SBYB bits to go into Active Altimeter mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1,(CTRL_REG_1_DATA | ALT_MASK | ACTIVE_MASK));
interrupt void (void)
{
/*
** Clear the interrupt flag
*/
CLEAR_MPL3115A2_INTERRUPT;
/** setting CHECK_INT flag to true
** allows us to handle the data interrupt
** in the main loop
*/
CHECK_INT = TRUE;
}
7.2
Pressure alarms
The Pressure alarms work exactly the same as the Altitude alarms in Section 7.1, “Altitude alarms” with
the difference being that the values of P_TGT_(MSB,LSB) and P_WND_(MSB,LSB) are unsigned 16-bit
values in 2 Pascal units.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
23
8
Temperature Alarm Interrupts
The MPL3115A2 provides two interrupt alarms for Temperature, a threshold alarm and a window alarm.
For the Threshold alarm, the interrupt flag is set on reaching the value stored in the Temperature target
register (T_TGT). Additionally, a window value (T_WND) provides the ability to signal when the target
is nearing the lower threshold, the target threshold or the upper threshold value set as offsets from the
Temperature target value.
The T_TGT register holds the Temperature target value, in °C, as a signed 8-bit value in 2's complement.
The T_WND register holds the offset value as an unsigned 8-bit value.
Examples:
• Set Temperature alert to 30°C and window value to 10°C, interrupt is asserted passing 20°C, 30°C,
and 40°C.
• The Window alarm interrupt flag is set when the temperature value is within the window defined
by the following equation:
Window = T_TGT  T_WND
8.1
Eqn. 2
Setting threshold alarm for target temperature
To set the temperature alarm so that the interrupt goes off only at the target temperature we must set the
T_TGT register to our target in °C and set the window register T_WND to zero. We then enable the
Temperature threshold interrupt by writing a 1 to bit 2 (INT_EN_TTH) of CTRL_REG4 (Interrupt Enable
register) and routing the interrupt to pin INT2 by writing a zero to bit 2 (INT_CFG_TTH) of CTRL_REG5
(Interrupt Configuration register).
Example 17.
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
/*
** Write Target and Window Values
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
24
Freescale Semiconductor, Inc.
** value[2] is set to 0
*/
IIC_RegWrite(SlaveAddressIIC, T_TGT, value[1]);
IIC_RegWrite(SlaveAddressIIC, T_WND, value[2]);
/*
** Enable Interrupt and Map to Interrupt Pin
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_TTH_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_TTH_MASK);
/*
** Write a 1 to the SBYB bits to go into Active mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | ACTIVE_MASK));
interrupt void isr_MPL3115A2 (void)
{
/*
** Clear the interrupt flag
*/
CLEAR_KBI_INTERRUPT;
/** setting CHECK_INT flag to true
** allows us to handle the data interrupt
** in the main loop
*/
CHECK_INT = TRUE;
}
8.2
Setting threshold alarm for upper and lower thresholds
To set the Temperature alarm so that the interrupt goes off at the target temperature as well as at the lower
and upper thresholds we must set the T_TGT register to our target in °C and set the window register
T_WND to the desired offset. We then enable the Temperature Threshold interrupt by writing a 1 to bit 2
(INT_EN_TTH) of CTRL_REG4 (Interrupt Enable register) and routing the interrupt to pin INT2 by
writing a zero to bit 2 (INT_CFG_TTH) of CTRL_REG5 (Interrupt Configuration register).
Example 18.
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
25
*/
temp
temp
temp
temp
temp
temp
=
=
=
=
=
=
IIC_RegRead(SlaveAddressIIC,
IIC_RegRead(SlaveAddressIIC,
IIC_RegRead(SlaveAddressIIC,
IIC_RegRead(SlaveAddressIIC,
IIC_RegRead(SlaveAddressIIC,
IIC_RegRead(SlaveAddressIIC,
OUT_P_MSB_REG);
OUT_P_CSB_REG);
OUT_P_LSB_REG);
OUT_T_MSB_REG);
OUT_T_LSB_REG);
F_STATUS);
/*
** Write Target and Window Values
** value[2] are set to the offset
*/
IIC_RegWrite(SlaveAddressIIC, T_TGT, value[1]);
IIC_RegWrite(SlaveAddressIIC, T_WND, value[2]);
/*
** Enable Interrupt and Map to Interrupt Pin
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_TTH_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_TTH_MASK);
/*
** Write a 1 to the SBYB bits to go into Active mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | ACTIVE_MASK));
interrupt void isr_MPL3115A2 (void)
{
/*
** Clear the interrupt flag
*/
CLEAR_KBI_INTERRUPT;
/** setting CHECK_INT flag to true
** allows us to handle the data interrupt
** in the main loop
*/
CHECK_INT = TRUE;
}
8.3
Setting the window alarm
To set the Temperature alarm so that the interrupt goes off only when we are in the window defined by
T_TGT ± T_WND we must set the T_TGT register to our target in °C and set the window register T_WND
to the desired offset. We then enable the Temperature Window interrupt by writing a 1 to bit 4
(INT_EN_TW) of CTRL_REG4 (Interrupt Enable register) and routing the interrupt to pin INT2 by
writing a zero to bit 4 (INT_CFG_TW) of CTRL_REG5 (Interrupt Configuration register).
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Freescale Semiconductor, Inc.
Example 19.
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
/*
** Write Target and Window Values
** value[1] and value[2] are set to the offset
*/
IIC_RegWrite(SlaveAddressIIC, T_TGT, value[1]);
IIC_RegWrite(SlaveAddressIIC, T_WND, value[2]);
/*
** Enable Interrupt and Map to Interrupt Pin
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_TW_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_TW_MASK);
/*
** Write a 1 to the SBYB bits to go into Active mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (CTRL_REG_1_DATA | ACTIVE_MASK));
interrupt void isr_MPL3115A2 (void)
{
/*
** Clear the interrupt flag
*/
CLEAR_KBI_INTERRUPT;
/** setting CHECK_INT flag to true
** allows us to handle the data interrupt
** in the main loop
*/
CHECK_INT = TRUE;
}
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
27
9
Using the 32-sample FIFO
9.1
Introduction
The MPL3115A2 has a built-in 32-sample first in, first out (FIFO) buffer capable of storing the 20-bit
pressure data and the 12-bit Temperature data. The FIFO is very beneficial for saving overall system power
by putting the processor into sleep mode until it needs to process data from the sensor. The idea is to
configure the MPL3115A2 to monitor a desired interrupt, putting the processor into a low-power mode
until it needs to respond to the sensor. This minimizes the system’s overall power consumption, increasing
the life of the battery. The embedded FIFO is a proven benefit as it limits how often the processor needs
to read the data. The FIFO allows the processor to sleep longer while samples are being collected inside
the sensor. Higher sample-rate data can be captured in the FIFO and accessed at a reasonable update time
without increasing computational throughput by accessing every sample individually.
9.2
•
•
•
•
9.3
Summary
The embedded FIFO is highly beneficial for system power savings and minimizing traffic across
the I2C bus.
The FIFO allows for remarkable power savings of the system by allowing the host processor/MCU
to go into a sleep mode while the pressure sensor independently stores the data, up to 32 samples.
The FIFO can be configured to be in a circular buffer mode or a fill buffer mode.
The FIFO allows you to log data for up to 12 days using the highest ST setting of 9 hours.
Embedded settings of the FIFO
The following sections discuss the different registers involved in configuring the FIFO.
• Section 9.3.1, “F_SETUP register (0x0F)”
• Section 9.3.2, “Setting up the FIFO interrupt”
• Section 9.3.3, “F_STATUS register (0x0D)”
• Section 9.3.4, “F_DATA register (0xE)”
• Section 9.3.5, “Setting the interrupts for FIFO”
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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9.3.1
F_SETUP register (0x0F)
The FIFO mode and the watermark is specified in the F_SETUP register. The FIFO can be configured in
either a circular buffer or in overflow mode. In circular buffer mode a watermark can be set to trigger a
flag event. Exceeding the watermark count does not stop the FIFO from accepting new data, the oldest data
is overwritten.
F_SETUP
7
6
5
4
3
2
1
0
F_MODE1
F_MODE0
F_WMRK5
F_WMRK4
F_WMRK3
F_WMRK2
F_WMRK1
F_WMRK0
0
0
0
0
0
0
0
0
R
W
Reset
Figure 9. FIFO setup register
9.3.2
Setting up the FIFO interrupt
In order to setup the FIFO interrupt event the INT_EN_FIFO bit of CTRL_REG4 must be set and the
INT_CFG_FIFO bit of CTRL_REG5 must be set to route the interrupt to INT1 or INT2.
9.3.3
F_STATUS register (0x0D)
The FIFO status register indicates the current status information of the FIFO subsytem.
F_STATUS
R
7
6
5
4
3
2
1
0
F_OVF
F_WMRK_FLAG
F_CNT5
F_CNT4
F_CNT3
F_CNT_2
F_CNT_1
F_CNT_0
0
0
0
0
0
0
0
0
W
Reset
Figure 10. FIFO status register
Table 4. FIFO Flag Event Descriptions
F_OVF
F_WMRK_FLAG
Result
0
—
No FIFO overflow event detected
1
—
FIFO overflow event detected
—
0
No FIFO watermark event detected
—
1
FIFO watermark event detected
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
29
The F_OVF and F_WMRK_FLAG remain asserted while the event source is still active, but the user can
clear the FIFO interrupt bit flag in the INT_SOURCE register be reading the F_STATUS register.
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 greater than the F_WMRK
value.
Table 5. FIFO Sample Count Description
Name
Description
FIFO sample counter. Indicates the number of samples currently stored in the FIFO.
000000 indicates that the FIFO is empty
000001 to 100000 indicates 1 to 32 samples stored in the FIFO
F_CNT[5:0]
9.3.4
F_DATA register (0xE)
F_DATA is a read-only register which provides access to FIFO data. FIFO holds a maximum of 32 P/T
samples. Each sample consists of 5 bytes; 3 bytes of pressure data and 2 bytes of temperature data. A
maximum of 5 x 32 = 160 data bytes of samples can be stored. When F_MODE bit in FIFO SETUP
(F_SETUP) register is set to logic “1”, the F_DATA pointer shares the same address location as
OUT_P_MSB (0x01); therefore all accesses of the FIFO buffer data use the I2C sub register address of
0x01. Reads from the other data registers (0x02, 0x03, 0x04, 0x05) will return a value of 0x00. The FIFO
will not suspend data accumulation during reads to F_DATA register. All 160 bytes of data can be read out
using a multibyte I2C read subroutine.
F_DATA 8-bit Data Access Register
7
6
5
4
R
3
2
1
0
0
0
0
0
F_DATA
W
Reset
0
0
0
0
Figure 11. FIFO Data Register
Table 6. Read accesses through F_DATA
1st Read
OUT_P_MSB (oldest)
2nd Read
OUT_P_CSB (oldest)
3rd Read
OUT_P_LSB (oldest)
4th Read
OUT_T_MSB (oldest)
5th Read
OUT_T_LSB (oldest)
.
.
.
.
.
.
OUT_T_LSB (oldest)
0x00
0x00
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Freescale Semiconductor, Inc.
9.3.5
Setting the interrupts for FIFO
In order to enable the FIFO interrupt you must write a 1 to bit 6 (INT_EN_FIFO) of the interrupt enable
register CTRL_REG4 (0x29). The interrupt configuration register CTRL_REG5 controls which interrupt
the flag goes to writing a 1 to bit 6 (INT_CFG_FIFO) of this register will send the flag to INT1 pin and
writing a 0 will send it to INT2 pin.
9.4
Setting up the FIFO in Overflow mode
To setup the FIFO in overflow mode we will configure the F_MODE[1:0] bits of the F_SETUP(0x0F)
register to 10, setup the interrupt flag to go to INT2 and look for the F_OVF bit in the F_STATUS register.
Example 20.
/*
** Read contents of CNTL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
/*
** Clear FIFO MODE by writing a 00 to F_MODE[1:0]
*/
IIC_RegWrite(SlaveAddressIIC, F_SETUP_REG, F_CLEAR_MASK);
/*
** Setup the FIFO to Overflow Mode
** Route to INT2
** Open Drain Active Low Interrupts
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG3, (PP_OD1_MASK | PP_OD2_MASK));
IIC_RegWrite(SlaveAddressIIC, F_SETUP_REG, F_MODE10_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_FIFO_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_CLEAR);
/*
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
31
** Put part into Active mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (IIC_RegRead(SlaveAddressIIC, CTRL_REG1) |
ACTIVE_MASK));
/******************************************************/
/* MPL3115A2 Interrupt Service Routine for the FIFO
/
/******************************************************/
interrupt void isr_MPL3115A2 (void)
{
/*
** Clear the MCUs interrupt flag
*/
CLEAR_MPL3155A2_INTERRUPT;
/*
** Go read interrupt source register
*/
RegisterFlag.Byte = IIC_RegRead(SlaveAddressIIC, INT_SOURCE_REG);
if(RegisterFlag.SRC_FIFO_BIT == 1)
{
RegisterFlag.Byte = IIC_RegRead(SlaveAddressIIC, F_STATUS_REG);
/*
** Go read FIFO with a single multi-byte IIC access
*/
value[4] = (RegisterFlag.Byte & F_CNT_MASK) * 5;
IIC_RegReadN(SlaveAddressIIC, OUT_P_MSB_REG, value[4],
&fifo_data[0].Sample.BT.b_msb);
}
}
The interrupt routine dumps the FIFO into an array for further processing. This method is not ideal and is
used only to illustrate the multibyte read. The ideal method is to set a flag in the interrupt service routine
and then use a task or function to handle the flag.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Freescale Semiconductor, Inc.
9.5
Setting the FIFO with a Watermark
To setup the FIFO in watermark mode we will configure the F_MODE[1:0] bits of the F_SETUP(0x0F)
register to 01, setup the interrupt flag to go to INT2, write a watermark value to F_WMRK[5:0] of the
F_SETUP register and look for the F_WMRK_FLAG bit in the F_STATUS register.
Example 21.
/*
** Read contents of CTRL_REG_1
** Clear SBYB mask while holding all other values of CTRL_REG_1.
** To put part into Standby mode
*/
CTRL_REG_1_DATA = IIC_RegRead(SlaveAddressIIC, CTRL_REG1);
IIC_Reg_Write(SlaveAddressIIC, CTRL_REG1, CTRL_REG_1_DATA & STANDBY_SBYB_MASK);
/*
** Clear all interrupts by reading the output registers.
** Enable the Data Ready Interrupt and route to INT 1
** Activate sensor in Altimeter mode.
*/
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_CSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_P_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_MSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, OUT_T_LSB_REG);
temp = IIC_RegRead(SlaveAddressIIC, F_STATUS);
/*
** Clear FIFO MODE by writing a 00 to F_MODE[1:0]
*/
IIC_RegWrite(SlaveAddressIIC, F_SETUP_REG, F_CLEAR_MASK);
/*
** Setup the FIFO to Watermark Mode
** Write a watermark value
** Route to INT2
** Open Drain Active Low Interrupts
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG3, (PP_OD1_MASK | PP_OD2_MASK));
value[1] =0x05;
IIC_RegWrite(SlaveAddressIIC, F_SETUP_REG, (F_MODE01_MASK | value[1]));
IIC_RegWrite(SlaveAddressIIC, CTRL_REG4, INT_EN_FIFO_MASK);
IIC_RegWrite(SlaveAddressIIC, CTRL_REG5, INT_CFG_CLEAR);
/*
** Put part into Active mode
*/
IIC_RegWrite(SlaveAddressIIC, CTRL_REG1, (IIC_RegRead(SlaveAddressIIC, CTRL_REG1) |
ACTIVE_MASK));
We use the same interrupt routine as the Overflow mode to dump the FIFO.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
33
10
Command Line Interface User Guide
The command line interface driver code provides the customer with a starting point to develop their own
application specific code. The code was written on the CodeWarrior development suite. Download the
code via the BDM to the DEMOSTB MPL3115A2. An image of the demo board is shown:
Figure 12. MPL3115A2 daughter board, LFSTBEBMPL3115A2 evaluation board and
the LSTBUS interface board
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
34
Freescale Semiconductor, Inc.
Once the code is loaded into the microcontroller start a HyperTerminal Window with the following
settings:
• Bits per second: 115200
• Data bits: 8
• Parity: None
• Stop bits: 1
• Flow Control: None
• Once connected, a carriage return will initiate the command line interface.
• To see a list of commands type a “?” in the terminal window.
List of MPL3115A2 commands:
Mn
:
CC
:
CW
:
RR xx
:
RW xx = nn :
RO n
:
RT n
:
RF
:
Sx
:
I n
:
AAn xx yy wm
APn xx yy wm
ATn xx wm
FO
FW ww
10.1
•
•
•
•
Mode 0=Standby; 1=Active;2=Alt;3=Bar
Check Status/Control Registers
Check Alarm Registers
Register xx Read
Register xx Write value nn
OSR Ratio 0=1;1=2;2=4;3=8;4=16;5=32;6=64;7=128
ST Time Step 0=2^0;1=2^1;2=2^2;3=2^3;...;A=2^A;....F=2^F
Report OSR and Time Step and Mode
Stream Data Polling
Stream via INTn
wl : Altitude Alarm
wl : Pressure Alarm
: Temp and Window alarm
: n 1= INT1; 2= INT2
: xx: Target MSB; yy: Target LSB
: wm: Window MSB; wl: Window LSB
: Stream via FIFO Overflow mode
: Watermark Mode
: ww: Watermark= 1 to 32
Modes
M0 - Standby
M1 - Active
M2 - Altimeter
M3 - Barometer
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
35
10.2
Register commands
10.2.1
Check Status and Check Window registers
The CC command lists out the contents of the following registers:
• Status Register (0x00/0x06)
• CTRL_REG1 (0x26)
• CTRL_REG2 (0x27)
• CTRL_REG3 (0x28)
• CTRL_REG4 (0x29)
• CTRL_REG5 (0x2A)
• System Mode Register (0x11)
• Interrupt Source Register (0x12)
The CW command lists the contents of the following registers:
• Altitude/Pressure Target MSB (0x16)
• Altitude/Pressure Target LSB (0x17)
• Altitude/Pressure Window MSB (0x19)
• Altitude/Pressure Window MSB (0x1A)
• Temperature Target (0x18)
• Temperature Window (0x1B)
10.2.2
Register Read
The RR command either lists the content of all registers in tabular format or if specified the contents of a
single register i.e. RR 12 will list the contents of the Interrupt Source Register
10.2.3
Register Write
The RW command writes a value to a specific register i.e. RW 29 = 00
10.2.4
OSR Ratio
The RO command changes the OSR ratio i.e. RO 7 will change the OSR ratio to 128.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
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Freescale Semiconductor, Inc.
10.2.5
ST (Time Step) Ratio
The RT command changes the acquisition time step i.e. RT 2 will change the ST to 4 seconds.
Table 7. Time Step
Power
Time in
Seconds
20
0
21
2
22
4
23
8
24
16
25
32
26
64
27
128
28
256
9
512
2
2A
1024
2B
2048
2C
4096
2D
8192
2E
16384
2F
32768
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
37
10.3
Alarms
10.3.1
Altitude/Pressure Alarms
To setup a threshold alarm at 300 meters on INT1:
AA1 01 2C
To setup a threshold and window alarm at a target of 300 meters with a delta of 20 meters on INT2:
AA2 01 2C 00 14
10.3.2
Temperature Alarms
To setup a threshold alarm at 25°C on INT1:
AT1 19
To setup a threshold and window alarm at a target of 25°C with a delta of 5°C on INT2:
AT2 19 05
10.4
FIFO Commands
The FO command will stream data via FIFO Overflow mode. The FW xx command will stream data via
FIFO Watermark mode with the watermark set to xx i.e. FW 05 will set the watermark to 5.
10.5
Related Documentation
The MPL3115A2 device features and operations are described in a variety of reference manuals, user
guides, and application notes. To find the most-current versions of these documents:
1. Go to the Freescale homepage at:
http://www.freescale.com/
2. In the Keyword search box at the top of the page, enter the device number MPL3115A2.
3. In the Refine Your Result pane on the left, click on the Documentation link.
Data Manipulation and Basic Settings of the MPL3115A2 Command Line Interface Driver Code, Rev 0.1
Freescale Semiconductor, Inc.
38
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