read

Read data from I2C device

Description

example

data = read(myi2cdevice,count,dataPrecision) returns data from the I2C device as a row vector.

The read method stops when it finishes reading the specified data from the device, or when the timeout period elapses.

Examples

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You can connect and exchange data with a pair of I2C devices.

Create a connection from the MATLAB® software to the Raspberry Pi™ board.

mypi = raspi
mypi = 

  Raspi with Properties:

           DeviceAddress: 'raspberrypi-hysdu8X38o'
                    Port: 18725
               BoardName: 'Raspberry
        Pi Model B Rev 2'
           AvailableLEDs: {'led0'}
    AvailableDigitalPins: [4 7 8 9 10 11 14 15 17 18 22 23 24 25 27 30 31]
    AvailableSPIChannels: {}
      AvailableI2CBuses: {'i2c-0'  'i2c-1'}
             I2CBusSpeed: 100000

  Supported peripherals

Redisplay AvailableI2CBuses and I2CBusSpeed.

mypi.AvailableI2CBuses
mypi.I2CBusSpeed      
ans =

  1×2 cell array 

    {'i2c-0'}    {'i2c-1'}

ans =

      100000

Show the location of the I2C pins.

showPins(mypi)

The pin map shows that, for this model and revision of the board, the i2c-1 bus is available on the GPIO header pins I2C1_SDA (GPIO 2) and I2C1_SCL (GPIO 3).

After physically connecting your I2C device to the I2C pins, get the addresses of I2C devices attached to the I2C bus, 'i2c-1'.

scanI2CBus(mypi,'i2c-1')
ans = 

     {'0x55','0x20'}

Create a connection, i2csensor, from the MATLAB software to the I2C sensor at '0x20'.

i2csensor = i2cdev(mypi,'i2c-1','0x20')
i2csensor = 

I2C with Properties:
     Bus: i2c-1
    I2CAddress: 0x20
       TimeOut: 10

Read two uint8 numbers from the sensor.

output1 = read(i2csensor,2)

Read the value of register 14 from the sensor.

output2 = readRegister(i2csensor,14)

Create a connection, i2cdisplay, from the MATLAB software to the I2C LED display at '0x55'.

i2cdisplay = i2cdev(mypi,'i2c-1','0x55')
i2cdisplay = 

I2C with Properties:
     Bus: i2c-1
    I2CAddress: 0x55
       TimeOut: 10

Write characters to the display.

write(i2cdisplay,[hex2dec('20') hex2dec('51')])

Write a scalar hexadecimal value, hex2dec('08'), to register 3 on an I2C device.

writeRegister(i2cdisplay,3,hex2dec('08'),'uint8')

If you are not using I2C, disable I2C to free additional GPIO pins.

disableI2C(mypi)

Before using I2C again, enable I2C.

enableI2C(mypi)

When you enable I2C, you can change the mypi.I2CBusSpeed property.

disableI2C(mypi)
enableI2C(mypi,400000)
mypi.I2CBusSpeed
ans =

       40000

Input Arguments

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Connection to I2C device, specified as a i2cdev object.

Example: myi2cdevice

Size of I2C data, specified as a scalar. This value is the number of data elements that you expect.

Example: 2

Data Types: int8 | int16 | uint8 | uint16

Data precision, specified as a string. Match the data precision to the size of the register on the device. Optional.

Example: 'int16'

Data Types: char

Output Arguments

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Data from the I2C device, returned as a row vector. The count argument specifies the number of elements in the row vector.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.