The most recent I2C bus specification (revision 4) was released at February 2012. In this I2C specification NXP Semiconductors introduced the unidirectional I2C bus and Ultra Fast-mode (UFm), with I2C bit rate up to 5 Mbit/s.
Ultra Fast-mode devices use push-pull drivers (the bidirectional bus requires open-drain output buffers) and eliminates the pull-up resistors. Ultra Fast-mode I2C devices are not compatible with I2C specification for bidirectional bus.
I2C Bus Specification History
The original I2C bus specification was released in 1982 by Philips Semiconductors. Its main purpose was to provide an easy way to connect a CPU to peripheral chips in a TV-set. Philips Semiconductors was one of the main manufacturers of consumer electronics in the early 1980's. This version of I2C specification covered Standard mode and Low-speed mode. The low speed mode has been omitted in the version 1.0 of I2C specification.
At 1992 Philips Semiconductor released the I2C Bus Specification Version 1.0. In this version of I2C specification Philips Semiconductor removed the low-speed mode and added the Fast-mode (bit rate up to 400 kbis/s). In addition to 7-bit addressing, 10-bit addressing was introduced (to allow additional 1024 slave addresses).
At April 1995 Philips Semiconductor published the application note "The I2C-bus and how to use it (including I2C specifications)"
At December 1998 Philips Semiconductor released The I2C Bus Specification Version 2.0. The major changes in this version include addition of High-speed mode (I2C transfer rate up to 3.4 Mbit/s) and usage of bus voltage related levels instead of fixed input levels.
At August 1999 Philips Semiconductors published the list of assigned I2C addresses.
At January 1990 Philips Semiconductors reviewed some timing parameters for High-speed mode and released The I2C Bus Specification Version 2.1. The clock stretching after the START condition was also enabled in this I2C specification release.
At January 2003, at DesignCon 2003 in San Jose, Philips Semiconductor presented the I2C Manual. This I2C manual contains overview of different serial buses, their pros and cons and practical hints for I2C bus implementation and usage.
At 1st September 2006, Philips Semiconductors CEO Frans van Houten revealed that the company will move forward as NXP Semiconductors. From this date all updates to I2C specification were published under the new company name.
At June 2007 NXP Semiconductors released the version 3 of I2C specification. In this version, they introduced the Fast-mode Plus (Fm+) specification. The Fast-mode Plus supports I2C transfers with the rate up to 1 Mbit/s. NXP Semiconductors also moved level shifting information to a separate application note.
- Download I2C Bus Specification (version 3.0)
- Download application note "Level shifting techniques in I2C bus design"
Finally, at February 2013, NXP Semiconductors released The I2C Bus Specification Version 4. In this version was added the unidirectional bus and Ultra Fast-mode (UFm), with a bit rate up to 5 MBit/s. This is the latest version of the I2C bus specification.
USB-I2C Adapters that conform to I2C Bus Specification
All DLN-series PC-I2C adapters conform to I2C Bus Specification (ver. 4) Fast-mode transfer rate.
DLN-1 and DLN-2 USB-I2C adapters also conform to Fast-mode Plus specification (I2C interface speed up to 1 Mbit/s).
We have tested DLN-4M and DLN-4S adapters at frequencies up to 1 MHz and have proved to work well, but their I2C lines have 6 mA current limitations. This limitation can affect I2C bus communication at Fast-mode Plus speed if long wires are used or many slave devices are connected to the same USB-I2C adapter.