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  1.   Abstract
  2.   Trademarks
  3. 1I2C Overview
    1. 1.1 History
    2. 1.2 I2C Speed Modes
  4. 2I2C Physical Layer
    1. 2.1 Two-Wire Communication
    2. 2.2 Open-Drain Connection
    3. 2.3 Non-Destructive Bus Contention
  5. 3I2C Protocol
    1. 3.1 I2C START and STOP
    2. 3.2 Logical Ones and Zeros
    3. 3.3 I2C Communication Frames
  6. 4I2C Examples
    1. 4.1 DAC80501 Example
      1. 4.1.1 DAC80501 DAC Data Register
      2. 4.1.2 DAC80501 I2C Example Write
    2. 4.2 ADS1115 Example
      1. 4.2.1 ADS1115 Configuration Register
      2. 4.2.2 ADS1115 I2C Example Read
      3. 4.2.3 ADS1115 Conversion Result
  7. 5Reserved Addresses
    1. 5.1 General Call
    2. 5.2 START Byte
    3. 5.3 C-Bus Address, Different Bus Format, Future Purposes
    4. 5.4 HS-Mode Controller Code
    5. 5.5 Device ID
    6. 5.6 10-Bit Target Addressing
      1. 5.6.1 10-Bit Target Addressing Write
      2. 5.6.2 10-Bit Target Addressing Read
  8. 6Advanced Topics
    1. 6.1 Clock Synchronization and Arbitration
    2. 6.2 Clock Stretching
    3. 6.3 Electrical Specifications
    4. 6.4 Voltage Level Translation
      1. 6.4.1 Example 1
      2. 6.4.2 Example 2
      3. 6.4.3 Example 3
      4. 6.4.4 Example 4
    5. 6.5 Pullup Resistor Sizing
      1. 6.5.1 Minimum Pullup Resistance Sizing
      2. 6.5.2 Maximum Pullup Resistance Sizing
  9. 7Protocols Similar to I2C
  10. 8Summary

7 Protocols Similar to I2C

The I2C specification discusses several other communications protocols based on I2C. These other protocols can be similar and compatible with I2C communication and can be used for specific applications. Some protocols also have defined sets of commands and application-specific extensions for their systems. This section briefly describes the applications for these other protocols, but their systems, applications, and uses are found elsewhere.

The first of these similar protocols is the Two Wire Interface or TWI. This protocol is basically the same as I2C. However, there are some minor differences in that TWI does not support a START byte and does not support high-speed modes. Generally, TWI-compatible devices are expected to be compatible with I2C and the protocol can be seen with the same logic analyzers.

The System Management bus or SMBus® is a protocol similar to I2C that is tailored to a specific function. SMBus is commonly used in servers and computer motherboards for power source management. The protocol is very similar to I2C in the communication protocol, and can be understood by an I2C controller.

The SMBus protocol has some additional features in comparison to I2C. The SMBus can dynamically set addresses, allowing for quick communications at the start up of a system. Also, the bus has a 35-ms timeout which prevents one device from indefinitely tying up the bus. The protocol also has a packet error checking for error detection in data communication. There is an additional line called SMBAlert that is used by target devices as an interrupt to tell the controller about certain events detected by the target device.

The Power Management bus or PMBus® is a variant of SMBus defined by Intel. PMBus is used in the digital management of power supplies. This protocol also defines specific commands to retrieve data about voltage, current, and power in the system.

Intelligent Platform Management Interface or IPMI is another I2C-based protocol. This protocol is used by baseboard management controllers (BMC) for autonomous computer subsystems for monitoring and management of the system CPU, firmware, and operating system. The protocol uses a standardized message-based interface for a computer motherboard or server. The BMC is always running even when the main system is off. This allows for operation, measurement, and remote management of a system.

There are several other similar protocols discussed in the I2C specifications. Advanced Telecommunications Computing Architecture (ATCA) is a follow-on to Compact PCI and is used in rack-mounted telecom hardware. Display Data Channel (DDC) is a monitor or display information protocol used by hosts for control of display functions. Finally, C-Bus is another protocol that is derived from I2C. As mentioned in the reserved address section, this protocol is used in some parts of the world for home and building automation, but is generally not used in the United States.