Project Details

I²C is a popular data bus to communicate with inter-board peripherals. Today I²C based chips and modules are widely available in many categories, including data storage, ADC/DAC, I/O Expanders, sensors, etc.

The I²C master mode emulator allows communication with I²C devices by sending or receiving data to/from the I²C bus. To issue the I²C commands, the emulator should connect to a PC over the USB port. After initializing the emulator, the PC and directly control the I²C slave chip/module.

This emulator is base on ATmega16A MCU. The USB communication channel is develop using the V-USB firmware.

To simplify the assembly, the PCB of this emulator is designed on a single-side board. The dimensions of the PCB are 96.77mm × 110.73mm. All the parts used in this project are through-hole-type, generally available components.

This emulator needs an external power supply, and the recommended supply voltage is between 12V - 15V.

Control software and commands

The control software of the emulator is developed using libusb and tested only with Linux operating systems. The current firmware and control software support I²C emulation on 100kHz, 250kHz, and 400kHz clock rates.

Following commands are available for the I²C test terminal:

• init - To initialize the I²C bus with the given clock rate.
• start - Issue START condition to the I²C bus.
• stop - Issue STOP condition to the I²C bus.
• write - Write given byte value to the I²C bus.
• write-address - Set slave address with read/write flag.
• read - Read data byte received from the slave device.
• output-voltage - Command to set the output voltage to 5V or 3.3V.
• reset - Reset emulator and I²C bus.
• exit - Exit from the terminal application.
• help - Display help screen.

All the above commands are explained in the project documentation at the GitHub repository.

I²C test terminal has an auto-complete command prompt. To use this option, press the TAB key twice on the command prompt.

Before launch the terminal control application, the I²C Emulator device must connect to the PC and needs to power up.

Emulator test setup

The below diagram illustrates the simple layout to test the I²C terminal. In this layout I2C terminal is connected to the 24LC01 Serial EEPROM IC.

The basic test performs with the above setup are listed below:

I2C Terminal - Copyright (c) 2021 Dilshan R Jayakody. (jayakody2000lk@gmail.com)
Type "help" to list down the available commands. Enter "help [COMMAND]" to get the information about the specific command.
Current I2C output voltage: 3.3V
> init 100
> start
A START condition has been transmitted.
> write-address 0xA0
Slave address with WRITE flag has been transmitted, ACK has been received.
> write 0
Data byte has been transmitted, ACK has been received.
> write 0xAB
Data byte has been transmitted, ACK has been received.
> write 0xCD
Data byte has been transmitted, ACK has been received.
> write 0xEF
Data byte has been transmitted, ACK has been received.
> stop
> start
A START condition has been transmitted.
> write-address 0xA0
Slave address with WRITE flag has been transmitted, ACK has been received.
> write 0
Data byte has been transmitted, ACK has been received.
> start
A repeated START condition has been transmitted.
> write-address 0xA1
Slave address with READ flag has been transmitted, ACK has been received.
> read ack
Data byte has been received, ACK has been returned.
Data: 0xab
> read ack
Data byte has been received, ACK has been returned.
Data: 0xcd
> read ack
Data byte has been received, ACK has been returned.
Data: 0xef
> read nack
Data byte has been received, NOT ACK has been returned.
Data: 0xa1
> stop
> exit