What is I2C? How does it work? // Technology

What is I2C? How does it work? This is another QuickBits video giving you a brief overview of how I2C works.

[youtube https://www.youtube.com/watch?v=sOmMDJLx_ew&w=640&h=360]

A bit of history

I2C stands for Inter-Integrated Circuit and can also be called IIC or I squared C.

The initial I2C specification was created in 1982 and was designed to allow various Philips TTL, 5 volt ICs to communicate with each other at 100kHz. Revisions were added in later years that added faster bus modes, such as 400kHz, 3.4MHz and 5MHz.

  • 1992 – 400kHz “fast mode” – multi master
  • 1998 – 3.4MHz “high speed” – multi master
  • 2007 – 1MHz “fast mode” – multi master
  • 2012 – 5MHz “ultra fast” – single master

There are other variants to I2C.


This was a standard created by Atmel and other companies to avoid trademark conflicts. This standard is identical to I2C, but lacks a high speed mode.


There’s also SMBus, (latest specification here), which is a derivative of I2C developed by Intel which includes several differences:

  • Packet Error Checking (PEC).
  • Timeout for transfers.
  • Standardized transfer types.
  • ALERT line.
  • SUSPEND line.
  • Power down/up.
  • Max. bitrate of 100 kHz/s.


There’s also PMBus, which is a derivative of SMBus that adds power management capabilities.