📈I2C Protocol

Notes on I2C prorocol

Introduction

• Multi master multi slave communication , 128 devices maximum because of the data frame having a fixed bits for addresses

• Maximum of 3mbps , synchronous data transfer protocol

• has start and stop conditions , and a data frame format

configuration / connection

• Multi master multi slave

I2C connection

• SDA - Data line , SCL - Serial clock

• Open drain / open collector configuration / pull up pull down is required

• In open drain (above image) a pull up resistor is used for idle state and pulled low when required

• uses 4.7kohm resisitor typically

Details

Communication:

• start condition : SDA is pulled low keeping scl (clk) high (idle)

• Master sends 7 bit (0-127) slave address first with read/write and waits for ACK/NACK from slave

• slave pulls sda low to indicate ACK

• Master sends or recieves a data frame 8 bit waits for ack or nack

• slave ACK once recieved

• Master stop condition is issued: SDA is high before SCL

Arbitration / handling multiple slaves from collision

• In Multi master configuration SDA is monitored and if its low then devices wont send data

Usage and limitations

• As the name suggests its a very low speed communication meant for chip to chip in a pcb

• used in sensors , eeprom etc

• 400kbps in the fast mode

References:

TI i2c explanation

I2C Primer: What is I2C? (Part 1) | Analog Devices

Basics of the I2C Communication ProtocolCircuit Basics

SPI vs I2C Protocol Differences and Things to ConsiderSaleae Articles