Overview of the Different Versions of the I2C Specification

The very first specification dates back to the year 1982. It only covered Standard mode (up to 100 kbit/s) and 7-bit addressing. Extensions like Fast Mode, Hs-Mode or 10-bit addressing were added in later versions.

Version 1.0 - 1992

This version of the 1992 I2C-bus specification included the following modifications:

Programming of a slave address by software has been omitted. The realization of this feature was rather complicated and had not been used.
The "low-speed mode" has been omitted. This mode was, in fact, a subset of the total I2C-bus specification and did not need to be specified explicitly.
The Fast-mode was added. This allows a fourfold increase of the bit rate up to 400 kbit/s. Fast-mode devices are downwards compatible i.e. they can be used in a 0 to 100 kbit/s I2C-bus system.
10-bit addressing was added. This allows 1024 additional slave addresses.
Slope control and input filtering FOR FAST-MODE DEVICES was specified to improve the EMC behavior. NOTE: Neither the 100 kbit/s I2C-bus system nor the 100 kbit/s devices have been changed.

Version 2.0 - 1998

As the I2C-bus became a de facto world standard implemented in over 1000 different ICs and licensed to more than 50 companies, an update of the specification became necessary as many of the newer applications required higher bus speeds and lower supply voltages. This version 2.0 of the I2C-bus specification met those requirements and included the following modifications:

The High-speed mode (Hs-mode) was added. This allows an increase in the bit rate up to 3.4 Mbit/s. Hs-mode devices can be mixed with Fast- and Standard-mode devices on the one I2C-bus system with bit rates from 0 to 3.4 Mbit/s.
The low output level and hysteresis of devices with a supply voltage of 2 V and below has been adapted to meet the required noise margins and to remain compatible with higher supply voltage devices.
The 0.6 V at 6 mA requirement for the output stages of Fast-mode devices has been omitted.
The fixed input levels for new devices were replaced by bus voltage-related levels.
Application information for bi-directional level shifter was added.