SLVA704 June   2015 INA209 , INA219 , INA220 , INA220-Q1 , INA223 , INA226 , INA226-Q1 , INA228 , INA228-Q1 , INA230 , INA231 , INA233 , INA234 , INA237 , INA237-Q1 , INA238 , INA238-Q1 , INA3221 , INA3221-Q1 , LM8323 , LM8325-1 , LM8327 , LM8328 , LM8330 , LM8333 , LM8335 , OPT3001 , OPT3004 , P82B715 , P82B96 , PCA9306 , PCA9306-Q1 , PCA9515A , PCA9515B , PCA9518 , PCA9534 , PCA9534A , PCA9535 , PCA9536 , PCA9538 , PCA9539 , PCA9543A , PCA9544A , PCA9545A , PCA9546A , PCA9548A , PCA9554 , PCA9554A , PCA9555 , PCA9557 , PCF8574 , PCF8574A , PCF8575 , PCF8575C , TCA4311A , TCA5405 , TCA6408A , TCA6416A , TCA6418E , TCA6424A , TCA6507 , TCA8418 , TCA8418E , TCA8424 , TCA9406 , TCA9509 , TCA9517 , TCA9517A , TCA9534 , TCA9534A , TCA9535 , TCA9538 , TCA9539 , TCA9539-Q1 , TCA9543A , TCA9544A , TCA9545A , TCA9546A , TCA9548A , TCA9554 , TCA9554A , TCA9555 , TCA9617A , TCA9617B , TCA9800 , TCA9801 , TCA9802 , TCA9803

 

  1.   Understanding the I2C Bus
    1.     Trademarks
    2. 1 Electrical Characteristics
      1. 1.1 Open-Drain for Bidirectional Communication
        1. 1.1.1 Open-Drain Pulling Low
        2. 1.1.2 Open-Drain Releasing Bus
    3. 2 I2C Interface
      1. 2.1 General I2C Operation
        1. 2.1.1 START and STOP Conditions
        2. 2.1.2 Repeated START Condition
      2. 2.2 Data Validity and Byte Format
      3. 2.3 Acknowledge (ACK) and Not Acknowledge (NACK)
    4. 3 I2C Data
      1. 3.1 Writing to a Slave On The I2C Bus
      2. 3.2 Reading From a Slave On The I2C Bus

1.1.1 Open-Drain Pulling Low

As described in the previous section, the Open-Drain setup may only pull a bus low, or "release" it and let a resistor pull it high. Figure 3 shows the flow of current to pull the bus low. The logic wanting to transmit a low will activate the pull-down FET, which will provide a short to ground, pulling the line low.

busarchLow.gifFigure 3. Pulling the Bus Low With An Open-Drain Interface