I2C Protocol: (Inter-Integrated Circuits)

-> I2C is used to connect devices like microcontrollers, EEPROMs, I/O interfaces, and other peripheral devices in an embedded system. A microcontroller is often used as the master device, and other peripheral devices are used as slave devices.

=> It was originally designed by Philips Semiconductor in 1982. Recently, it is a widely used protocol for short-distance communication. It is also known as Two Wired Interface(TWI).

-> I2C combines the best features of SPI and UARTs. With I2C, you can?connect multiple slaves to a single master (like SPI) and you can have multiple masters controlling single, or multiple slaves. This is?really useful when you want to have more than one microcontroller logging data to a single memory card or displaying text to a single LCD.

SDA (Serial Data)?– The line for the master and slave to send and receive data.

SCL (Serial Clock)?– The line?that carries?the clock signal.

It uses only 2 bi-directional open-drain lines for data communication called SDA and SCL. Both these lines are pulled high.

According to I2C protocols, the data line can not change when the clock line is high, it can change only when the clock line is low. The 2 lines are open drain, hence a pull-up resistor is required so that the lines are high since the devices on the I2C bus are active low. The data is transmitted in the form of packets which comprises 9 bits.

-> The data transferring is done in messages, which are broken up into frames of data. The message includes address frame that contains the binary address of the slave, start/stop conditions, read/write bits and ACK/NACK between each data frame.

• Start Condition: In start condition, the SDA line switches from a high voltage (‘1’ bit) level to a low voltage level (‘0’ bit) before the SCL line switches from high to low.

• Address Frame/Slave Address: A 7-bit sequence unique to each slave that identifies the slave when the master device needs to send/receive data.
• Read/Write Bit: A single bit specifying whether the master is sending data to the slave (the bit is set to ‘0’) or requesting data from the slave (the bit is set to ‘1’)
• ACK/NACK Bit: Each frame in a message is followed by an acknowledge/not-acknowledge bit. If the physical address of any slave device matches with the address sent by the master device, an ACK bit is returned to the sender from the receiving device. (if matches the bit is set to ‘0’ otherwise it remains ‘1’)
• Stop Condition: When the required data blocks are transferred through the SDA line, the SDA line switches from a low voltage (‘0’ bit) level to a high voltage level (‘1’ bit) before the SCL line switches from high to low.

Single Master with Multiple Slaves:

Multiple Masters with Multiple Slaves:

Advantages :

• Can be configured in multi-master mode.
• Complexity is reduced because it uses only 2 bi-directional lines (unlike SPI Communication).
• Cost-efficient.
• It uses ACK/NACK feature due to which it has improved error handling capabilities.

Limitations :

• Slower speed.
• Half-duplex communication is used in the I2C communication protocol.

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