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Introduction to using I2C

Originally, the I2C bus was designed to interact within a small number of devices on a single card, such as to manage the tuning of a car radio or TV. The maximum allowable capacitance was set at 400pF to allow proper rise and fall times for optimum clock and data signal integrity with a top speed of 100kbps. In 1992, the standard bus speed was increased to 400kbps to keep up with the ever-increasing performance requirements of new ICs. The latest I2C specification, released in 1998, increased the top speed to 3.4Mbps. All I2C devices are designed to be able to communicate together on the same two-wire bus and system functional architecture is limited only by the imagination of the designer.
But while its application to bus lengths typically found within consumer products, such as PCs, cellular phones, car radios, and TV sets, grew quickly, only a few system integrators were using it to span a room or a building. The I2C bus is now being increasingly used in multiple card systems, such as a blade servers, where:
  • The I2C bus to each card needs to be isolatable to allow for card insertion and removal while the rest of the system is in operation
  • Many more devices need to be located onto the same card
  • The total device and trace capacitance could exceed 400pF.
New bus extension and control devices help expand the I2C bus beyond the 400pF limit of about 20 devices and help control more devices, even those with the same I2C address. These new devices are popular with designers as they continue to expand and increase the range of use of I2C devices in maintenance and control applications.
This web site focuses on general purpose devices like the General Purpose I/O Expanders, LED Blinkers, Temperature and Voltage Hardware Monitors, DIP Switch Replacements, Multiplexers, Bus Masters/Microcontrollers, Bus Repeater/Hub/Extenders, Serial EEPROMs, Voltage Level Translators, and Analog-to-Digital Converters.

I2C Features

  • Only two bus lines are required: a serial data line (SDA) and a serial clock line (SCL)
  • Each device connected to the bus is software-addressable by a unique address and simple master/slave relationships exist at all times; masters can operate as master-transmitters or as master-receivers
  • I2C is a true multi-master bus including collision detection and arbitration to prevent data corruption if two or more masters simultaneously initiate data transfer
  • Serial, 8-bit oriented, bi-directional data transfers can be made at up to 100kbit/s in the Standard-mode, up to 400kbit/s in the Fast-mode, or up to 3.4Mbit/s in the High-speed mode
  • On-chip filtering (50ns) rejects spikes on the bus data line to preserve data integrity
  • The number of ICs that can be connected to the same bus segment is limited only by a maximum bus capacitive loading of 400pF.

I2C Designer Benefits

  • Functional blocks on the block diagram correspond with the actual ICs; designs proceed rapidly from block diagram to final schematic
  • No need to design bus interfaces because the I2C-bus interface is already integrated on-chip
  • Integrated addressing and data-transfer protocol allow systems to be completely software-defined
  • The same IC types can often be used in many different applications
  • Design-time reduces as designers quickly become familiar with the frequently used functional blocks represented by I2C bus compatible ICs
  • ICs can be added to or removed from a system without affecting any other circuits on the bus
  • Fault diagnosis and debugging are simple; malfunctions can be immediately traced
  • Software development time can be reduced by assembling a library of reusable software modules.

I2C Manufacturers Benefits

  • The simple 2-wire serial I2C bus minimizes interconnections so ICs have fewer pins and there are not so many PCB tracks resulting in smaller and less expensive PCBs
  • The completely integrated I2C bus protocol eliminates the need for address decoders and other "glue logic"
  • The multi-master capability of the I2C bus allows rapid testing/alignment of end-user equipment via external connections to an assembly-line
  • Increases system design flexibility by allowing simple construction of equipment variants and easy upgrading to keep design up-to-date
  • The I2C-bus is a de-facto world standard that is implemented in over 1000 different ICs (NXP Semiconductors has over 400) and licensed to more than 70 companies.

Applications

There are some specific applications for certain types of I2C device such as TV or radio tuners but, in most cases, a general purpose I2C device can be used in many different applications because of its simple construction.

End Use Segment

  • Telecom: Mobile phones, Base stations
  • Data processing: PCs, Servers
  • Instrumentation: Portable instrumentation, Metering systems
  • Automotive: Dashboard, Infotainment
  • Consumer: Audio/video systems, Household electronics

Functions

More Information
Standard ICs quick find
I2C sections
See also