Transmitting Data Over the I2C Interface

The typical workflow involves adapter discovery, connection, communication, and cleanup. Discovery can be done only at the adapter level. You need to have either a Total Phase Aardvark host adapter or a NI USB-845x adapter board installed to use the i2c interface.

Aardvark Example

This example shows how to communicate with an EEPROM chip on a circuit board, with an address of 50 hex and a board index of 0, using the Aardvark adapter.

To communicate with an EEPROM chip:

Ensure that the Aardvark adapter is installed so that you can use the i2c interface.

instrhwinfo('i2c')

ans = 

  HardwareInfo with properties:

    InstalledAdaptors: {'Aardvark'  'NI845x'}
       JarFileVersion: 'Version 4.1'

Access to your hardware may be provided by a support package. Go to the Support Package Installer to learn more.

Look at the adapter properties.

instrhwinfo('i2c','Aardvark')

ans = 

  HardwareInfo with properties:

             AdaptorDllName: 'C:\Program Files\MATLAB\R2019b\toolbox\instrument\instrumentadaptors\win64\mwaardvarki2c.dll'
          AdaptorDllVersion: 'Version 4.1'
                AdaptorName: 'Aardvark'
              BoardIdsInUse: [1×0 double]
          InstalledBoardIDs: 0
       DetectedBoardSerials: {'2237482577 (BoardIndex: 0)'}
      ObjectConstructorName: 'i2c('Aardvark', BoardIndex, RemoteAddress);'
              VendorDllName: 'aardvark.dll'
    VendorDriverDescription: 'Total Phase I2C Driver'

Access to your hardware may be provided by a support package. Go to the Support Package Installer to learn more.

Make sure that you have the Aardvark software driver installed and that the aardvark.dll is on your MATLAB path. For details, see I2C Interface Usage Requirements and Guidelines.

Create the I2C object called eeprom, using the following properties.
```
% Vendor = aardvark
% BoardIndex = 0
% RemoteAddress = 50h

eeprom = i2c('aardvark',0,'50h')
```
```
   I2C Object : I2C-0-50h

   Communication Settings 
      BoardIndex          0
      BoardSerial         2237482577
      BitRate:            100 kHz
      RemoteAddress:      50h
      Vendor:             aardvark


   Communication State 
      Status:             closed
      RecordStatus:       off

   Read/Write State  
      TransferStatus:     idle
```
You must provide these three inputs to create the object. To identify the address of the chip, consult its documentation or data sheet. You can also find the address by scanning for instruments in the Test & Measurement Tool. In the tool, right-click the I2C node and select Scan for I2C adaptors. Any chips found by the scan is listed in the hardware tree. The listing includes the remote address of the chip.
Connect to the chip.
```
fopen(eeprom)
```
Write 'Hello World!' to the EEPROM chip. Data is written page-by-page in I2C. Each page contains eight bytes. The page address needs to be mentioned before every byte of data written.
The first byte of the string 'Hello World!' is 'Hello Wo'. Its page address is 0.
```
fwrite(eeprom,[0 'Hello Wo'])
```
The second byte of the string 'Hello World!' is 'rld!'. Its page address is 8.
```
fwrite(eeprom,[8 'rld!'])
```
Read data back from the chip using the fread function. The chip returns the characters sent to it.
To start reading from the first byte of the first page, write a zero to the i2c object.
```
fwrite(eeprom,0)
```
```
char(fread(eeprom,12))'
```
```
ans =

    'Hello World!'
```
Disconnect the I2C device and clear the object from the workspace.
```
fclose(eeprom)
clear eeprom
```

NI USB-845x Example

This example shows how to communicate with an Analog Devices^® ADXL345 sensor chip on a circuit board, using an address of 53 hex and a board index of 0 on a NI USB-845x adapter. In this case, the NI USB-845x adapter board is plugged into the computer (via the USB port), and a circuit board containing the sensor chip is connected to the host adapter board via wires. Note that the circuit has external pullups, as the NI USB-8451 adapter used in this example does not have internal pullups.

To communicate with a sensor chip:

Ensure that the NI USB-845x adapter is installed so that you can use the i2c interface.

instrhwinfo('i2c')

ans = 

  HardwareInfo with properties:

    InstalledAdaptors: {'Aardvark'  'NI845x'}
       JarFileVersion: 'Version 4.1'

Access to your hardware may be provided by a support package. Go to the Support Package Installer to learn more.

Look at the NI USB-845x adapter properties.

instrhwinfo('i2c','NI845x')

ans = 

  HardwareInfo with properties:

             AdaptorDllName: 'C:\Program Files\MATLAB\R2019b\toolbox\instrument\instrumentadaptors\win64\mwni845xi2c.dll'
          AdaptorDllVersion: 'Version 4.1'
                AdaptorName: 'NI845x'
              BoardIdsInUse: [1×0 double]
          InstalledBoardIDs: [1×0 double]
       DetectedBoardSerials: {0×1 cell}
      ObjectConstructorName: 'i2c('NI845x', BoardIndex, RemoteAddress);'
              VendorDllName: 'Ni845x.dll'
    VendorDriverDescription: 'National Instruments NI USB 845x Driver'

Access to your hardware may be provided by a support package. Go to the Support Package Installer to learn more.

Make sure that you have the NI USB-845x software driver installed. For details, see I2C Interface Usage Requirements and Guidelines.

Create the I2C object called i2cobj, using these properties:
```
% Vendor = NI845x
% BoardIndex = 0
% RemoteAddress = 53h

i2cobj = i2c('NI845x',0,'53h');
```
You must provide these three inputs to create the object. To identify the address of the chip, consult its documentation or data sheet. You can also find the address by scanning for instruments in the Test & Measurement Tool. In the tool, right-click the I2C node and select Scan for I2C adaptors. Any chips found by the scan is listed in the hardware tree. The listing includes the remote address of the chip.
Connect to the chip.
```
fopen(i2cobj)
```
Write to the sensor chip. Read the documentation or data sheet of the chip in order to know what the remote address is and other information about the chip. Usually chip manufacturers provide separate read and write addresses. The adapter boards only take one address (the read address) and handle conversions to read and write addresses.
In this case, the chip’s device ID register is at address 0, so you need to write a 0 to the chip indicating you would like to read or write to the register.
```
fwrite(i2cobj,0)
```
Read data back from the chip using the fread function. By sending one byte, you can read back the device ID registry. For this chip, the read-only device ID registry is 229.
```
fread(i2cobj,1)
```
```
ans = 

   229
```
Disconnect the I2C device and clear the object from the workspace.
```
fclose(i2cobj)
clear i2cobj
```