MATLAB Examples

Read temperature from an NXP FXOS8700CQ sensor available on NXP FRDM-K64F Hardware

This example shows you how to use Simulink Coder Support Package for NXP FRDM-K64F Board to configure and read temperature from an NXP FXOS8700CQ sensor which is a I2C based sensor.

Contents

Introduction

Simulink® Coder™ Support Package for NXP FRDM-K64F Board enables you to use the I2C Master Read/ I2C Master Write blocks to communicate with I2C based devices.

In this example, you will learn how to communicate to the NXP FXOS8700CQ sensor which is available on the NXP FRDM-K64F board. FXOS8700CQ is a small, low-power, 3-axis, linear accelerometer and 3-axis, magnetometer combined into a single package. This sensor is interfaced with the NXP FRDM-K64F board using the I2C bus.

For more details about the device, refer to the FXOS8700CQ datasheet.

This examples shows you how to use the I2C Master Read and I2C Master Write blocks to read the temperature value from the FXOS8700CQ. If you would like to read Accelerometer data or Magnetometer data from this sensor, you can use the FXOS8700 6-Axes Sensor block available in the NXP FRDM-K64F library.

Prerequisites

We recommend completing Getting Started with Simulink Coder Support Package for NXP FRDM-K64F Board and Code Verification and Validation with External Mode.

Required Hardware

To run this example, you will need the following hardware:

  • NXP FRDM-K64F Board
  • USB type A to Micro-B cable

Model

Task 1 - Configure the Model for NXP FRDM-K64F Hardware

In this task, you will configure the model for the NXP FRDM-K64F Hardware.

1. Open the Initialize and Read temperature from I2C sensor using NXP FRDM-K64F Hardware model.

2. In your Simulink model, click Simulation > Model Configuration Parameters to open Configuration Parameters dialog.

3. Select the Hardware Implementation pane and select NXP FRDM-K64F hardware from the Hardware board parameter list.

4. Click OK.

Task 2 - Configure the Model to Read Temperature

This task shows how to initialize configuration registers of the NXP FXOS8700CQ sensor to read the temperature data.

1. Open the Initialize and Read temperature from I2C sensor using NXP FRDM-K64F Hardware model.

2. Notice the two subsystems in the model:

  • The One_time_initialization subsystem executes only once at the first step of the execution of the model. For the rest of the execution time, the Execution_loop subsystem runs. This selective execution of subsystems is handled using the Unit Delay and the Enabled Subsystem blocks from the Simulink library.
  • The One_time_initialization subsystem performs 2 functions. It sets the mode of the sensor and activates the sensor.

4. Configure the I2C Master Write block to set the mode of the NXP FXOS8700CQ sensor:

  • According to the NXP FXOS8700CQ datasheet, the TEMP register of the FXOS8700CQ sensor gives a valid temperature reading, when the sensor is set to magnetometer mode or hybrid mode. The mode of the sensor can be set by writing to the 'm_hms' bits of the M_CTRL_REG1 register.
  • Open the I2C Master Write1 block.
  • The onboard FXOS8700CQ sensor is connected to the I2C Module of the processor via the pins PTE24 (SCL) and PTE25 (SDA). As seen in the FRDM K64F reference manual that these pins belong to I2C module 0. Hence, set the I2C module to 0.
  • Notice that the Slave address is set to '0x1D' and Slave register address is set to '0x5B'. It can be seen in the NXP FXOS8700CQ datasheet that '0x1D' is the slave address of the device and '0x5B' is the address of the register M_CTRL_REG1.
  • Set the Slave byte order parameter to Big Endian as the Configuration Register has a size of 8-bit whose value needs to be sent over the I2C bus using Big Endian.

5. Configure the I2C Master Write block to activate the NXP FXOS8700CQ sensor:

  • Open the I2C Master Write2 block in the One_time_initialization subsystem.
  • The I2C module and the Slave address are set to 0 and '0x1D' as explained in step 4 above.
  • Notice that the Slave register address is set to '0x2A'. It can be seen in the NXP FXOS8700CQ datasheet that '0x2A' is the address of the register CTRL_REG1.
  • The sensor is in standby mode after reset. You can set the sensor to Active mode by setting the active bit in the CTRL_REG1 to 1 as per the NXP FXOS8700CQ datasheet.

6. Notice the following in the One_time_initialization subsystem:

  • The Constant1 and Constant2 blocks holds the value of '0x01' to be written to the M_CTRL_REG1 and CTRL_REG1 registers. The sensor is set to 'magnetometer only' mode by writing '0b01' to the 'm_hms' bits of the M_CTRL_REG1 register.
  • The I2C Master Read1 and I2C Master Read2 blocks, which are connected to the Display blocks, helps to verify that the correct data is written to the Configuration Registers. The I2C Master Read block uses the same settings as the respective I2C Master Write block.
  • The priority of the I2C Master Write1 block is set to be higher than the the priority of the I2C Master Write2 block. This is to ensure that the mode of the sensor is set first and then activated. The priority of the I2C Master Write block is set to be higher than the priority of the respective I2C Master Read block, to ensure that you read the value of the Configuration Register after it is set. To set the Priority of a block, right click on the block > Properties > General > Priority. To know more about block priorities and their impact on block execution order, refer to Set Block Properties.

7. Open and observe the following in the Execution_loop subsystem:

  • Open the I2C Master Read block. As mentioned for the I2C Master Write block, notice that the I2C Module is set to 0 and Slave address is set to '0x1D'.
  • It can be seen in the NXP FXOS8700CQ datasheet that '0x51' is the address of the TEMP register, which contains the temperature value in eight-bit 2's complement form. Hence the Slave register address is set to '0x51', Data type and Data size (N) are set to 'int8' and '1' respectively.
  • The sensitivity of the sensor is 0.96 C/LSB. Therefore, the Gain block performs a multiplication by 0.96 to give the temperature value in degree Celsius (C).

Task 3 - Run the Model in External Mode

In this task, you will run the model in External mode to monitor the temperature. Refer the Code Verification and Validation with External Mode demo for more understanding on External Mode.

1. Change the Simulation mode on the toolbar of the model to External.

2. Click the Run button on the toolbar of the model to run it in External mode.

3. Open the One_time_initialization subsystem.

4. Verify that the Display blocks shows a value of '0x01' in hexadecimal corresponding to the desired Configuration Register value.

5. In the Execution_loop subsystem, monitor the Display block to observe the FXOS8700CQ temperature reading in degree Celsius. The onboard LED glows when the Display block in the model shows a temperature above 27 degree Celsius.

6. Change the threshold value in the Switch block according to your ambient temperature and click Apply. See the onboard LED glow when the temperature exceeds the new threshold value.

7. Click the Stop button in the Simulink model to end the External mode execution.

Other Things to Try

Follow the steps in this example to communicate to other I2C based sensors.

Summary

This example showed how to program your NXP FRDM-K64F board to configure and read temperature from an I2C based sensor. In this example you learned how to:

  • Communicate with an I2C based sensor.
  • Program the NXP FRDM-K64F board to write data to and read data from specific registers on the I2C based sensor.
  • Initialize the sensor with some advanced settings.

You can use this example as a reference to access other I2C based sensors.