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ADS7138: Configure to high speed mode

Part Number: ADS7138

Hi Team

In datasheet it is mentioned to configure ADS7138 to high speed mode by giving codes in I2C frames. How do we need to provide the codes from the master to enable the high speed mode

Thanks

Abishek

  • Hi Abishek,

    This is part of the I2C specification.  High-speed is enabled by sending any of the master codes (0x09, 0b, 0D or 0x0F) specified in the i2c spec (or ADS7138 datasheet). By default all i2c devices are in standard mode.

    • Start condition is sent
    • 8 bit ‘master code’ is sent at 400 kbit max
    • Master code is ‘not acknowledged’
    • Active master switches to high-speed communication
  • Hi Tom

    Thanks for your reply. We changed the slave address in the driver code of ADS7138 to master code(0x09) since in I2C frame format slave address comes after start bit. when we change the slave address we could not detect the ADC.

    Is this the correct way to update the master code?

    If we need to update in driver code where we to update the master code(whether in slave address or data bits)

    Please confirm the method

    Thanks

    Abishek V

  • Hi Abhishek,

    The I2C protocol specification provides the sequence of event for switching the I2C bus to high-speed mode. The sequence of events is:

    1. I2C byte 1 (I2C bus is in 100kHz or 400kHz mode)
      1. I2C controller (MCU) sends start condition
      2. I2C controller (MCU) sends any one of the master codes for high-speed mode
      3. This command is not acknowledged (ACK bit will be high) -> all devices on the I2C bus that support high-speed mode will switch to high-speed mode.
    2. I2C byte 2 (I2C bus is in 3.4MHz mode after byte 1)
      1. I2C controller (MCU) sends repeat start condition (basically start condition again)
      2. I2C controller (MCU) sends ADS7138 address
      3. ADS7138 will acknowledge this command.
    3. Continue high-speed communication
    4. If at any point the I2C controller (MCU) sends stop condition, all devices on the I2C bus will exit high-speed mode of operation.

    Regards,
    Rahul