Basic I2C Communication

This example demonstrates the basic functionality of the TWI peripheral with a basic I2C communication, both reading and writing from/to the client devices. The device is connected to the PICkit Serial I2C Demo Board to communicate with the MCP3221 and MCP23008 I2C client devices. The AVR128DA48 will first scan the I2C bus to discover all devices available on the bus. A message will be transmitted through USART to indicate the addresses of the devices that respond with the acknowledge signal. A voltage will be read by the MCP3221 (equipped with a 12-bit ADC) and the result will be transmitted through I2C to the AVR128DA48 device. Then, the MCU will transmit an 8-bit sequence to the MCP23008, equipped with an I/O Expander, to drive 8 LEDs on an LED bar. The LED display (consisting in 8 LEDs) will indicate the potentiometer voltage value (divided in subranges). The software diagram of this application is presented in the figure below.

Related Documentation

• AVR128DA48 Product Family Page
• AVR128DA48 Data Sheet

Software Used

• MPLAB® X IDE 5.40 or newer (microchip.com/mplab/mplab-x-ide)
• MPLAB® XC8 2.20 or newer compiler (microchip.com/mplab/compilers)
• AVR_Dx-DFP 1.4.75 or newer

Hardware Used

• AVR128DA48 Curiosity Nano (DM164151)
• PICkit Serial I2C Demo Board (PKSERIAL-I2C1)
  • MCP3221
  • MCP23008

Setup

The AVR128DA48 Curiosity Nano Development Board is used as the test platform. The 12-ADC is used to transmit an analog value.

The following configurations must be made:

Pin	Configuration
PC2 (SCL)	Digital I/O
PC3 (SDA)	Digital I/O
PC0 (TX)	Digital output

Operation

1. Connect the board to the PC.

2. Open the avr128da48-cnano-i2c-send-receive-mplabx.X project in MPLAB® X IDE.

3. Set avr128da48-cnano-i2c-send-receive-mplabx.X project as main project. Right click on the project in the Projects tab and click Set as Main Project:

4. Select the AVR128DA48 Curiosity Nano in the Connected Hardware Tool drop down list of the project settings:

• Right click on the project and click Properties;
• Select the AVR128DA48 Curiosity Nano (click on the SN) in the Connected Hardware Tool list and then click OK:

5. Program the project to the board: right click on the project and click Make and Program Device:

6. Open the Data Visualizer plugin.
   

7. Select the AVR-DA COMn port and provide the correct configurations. Then, visualize the serial output on the terminal window. In this example, the I2C device scanning phase is described. The devices with the addresses 0x55, 0x56, and 0x57 responded with ACK.
   

After turning the potentiometer rotor one way and the other, the LEDs will indicate the level of that voltage, as presented below. The ADC conversion result is received from the 12-bit ADC - I2C client device, it is normalized (obtaining a 3-bit value to be indicated using the 8-LED bar), and the result is transmitted to the 8-bit I/O Expander - I2C client device.

Summary

This application shows how to use the TWI0 as an I2C compatible host to communicate with two I2C client devices:

• MCP3221 - equipped with a 12-bit ADC
• MCP23008 - equipped with an I/O Expander