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read

Read data from I2C device

Syntax

  • [data] = read(myi2cdevice,count,dataPrecision)

Description

[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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Connect and Exchange Data with I2C Devices

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

Create a connection to the Raspberry Pi™ board.

mypi = raspi
mypi = 

  Raspi with Properties:

           DeviceAddress: 'raspberrypi-computername'
                    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 = 

    '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 to the I2C sensor at '0x20' and assign that connection to a handle, i2csensor.

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 to the I2C LED display at '0x55' and assign that connection to a handle, i2cdisplay.

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 make additional GPIO pins available.

disableI2C(mypi)

When you use I2C again, enable I2C.

enableI2C(mypi)

You can only change the mypi.I2CBusSpeed property when you enable I2C.

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

       40000

Input Arguments

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myi2cdevice — Connection to I2C devicehandle

Connection to I2C device, specified as a handle.

Use i2cdev to create this connection.

Example: myi2cdevice

count — Size of I2C datasize of I2C data

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

dataPrecision — Data precision'uint8 (default) | 'int8' | 'int16' | '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 — vector of numeric valuesdata

Data from the I2C device, returned as a row vector. The number of elements of the row vector is specified by the count argument.

See Also

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