readRegister

Read from register on I2C device

Syntax

[value] = readRegister(myi2cdevice,register,dataPrecision)

Description

[value] = readRegister(myi2cdevice,register,dataPrecision) returns data from the register on the I2C device as a scalar.

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

Examples

Connect and Exchange Data with I2C Devices

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

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

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

myi2cdevice — Connection to I2C device

connection

Connection to I2C device, specified as a i2cdev object.

Example: myi2cdevice

register — I2C register number

I2C register number

I2C register number, specified as a scalar. This number is available from the device data sheet.

Example: 14

Data Types: double

dataPrecision — Data precision

'uint8' (default) | 'int8' | 'int16' | 'uint16' | 'int32' | 'uint32' | 'int64' | 'uint64' | 'single' | 'double'

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

value — Value of register

value of register

Value of the register, returned as a scalar.

Note

If the data read is bigger than uint8, the data is in little-endian format.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

• You can also deploy readRegister on the Raspberry Pi hardware in MATLAB Online™.