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LMK05318B: Float required on STATUS0 and STATUS1 required for SPI mode?

david royle
Intellectual 565 points
Part Number: LMK05318B


Entire datasheet indicates float on HW_SW_CTRL at rising edge PDN is used to configure EEPROM+SPI mode. However, note on page 7 indicates that float is also required on STATUS0 and STATUS1 at PDN rising edge.

We would like to have STATUS0 open collector with external pullup and EEPROM_SPI mode. Is the note saying that this combination is not possible?

  

  • 0
    TI__Expert 8625 points

    Hello David,

    When booting up in EEPROM + SPI mode, the STATUS pins must be floating on initial start. This means open collector with external pull up on the STATUS pins is not possible when first booting up in EEPROM + SPI mode.

    Regards,

    Kia Rahbar

  • 0 in reply to Kia Rahbar
    Intellectual 565 points

    Understood, but what is the rationale for this? Why would HW_SW_CTRL pin alone be able to provide this function?

  • 0 in reply to david royle
    TI__Expert 8625 points

    Hello David,

    In SPI mode, the STATUS pins are used for the device to determine it is being booted up in SPI. The three pins (HW_SW_CTRL, STATUS0, and STATUS1) momentarily operate as 3-level inputs to determine the SPI device start-up mode during POR.

    You can still use the STATUS pins as LVCMOS outputs when they are left floating.

    Regards,

    Kia Rahbar

  • 0 in reply to Kia Rahbar
    Intellectual 565 points

    Kia,

    I am curious about the rationale for involving STATUS0 and STATUS1. Why would three IO pins be needed vs. simply if HW_SW_CTRL is floating then we are in EEPROM+SPI mode as shown in table 6-2

  • +1 in reply to david royle
    TI__Expert 8625 points

    Hello David,

    The internal structure of our devices is designed to use the HW_SW_CTRL, STATUS0, and STATUS1 pins to select the boot up mode.

    Based off of the settings for these pins, the OP_MODE is set as shown below. OP_MODE is a read only register.

    In the I2C modes, the STATUS pins are don't care, but for SPI they need to be floating.

    This is how the internal boot up structure of our device was created by our design team.

    Regards,

    Kia Rahbar