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TCA9538 / PCA9538 Control register default value

Sunset
Genius 14125 points


Hello All,

once you reset the device all the registers goes to the default values.

  • Is there any default values for the control register as well?
  • In particular after the reset what is the pointer value (bit B0-B2)?


I want just to see if the device is in the bus with a dummy read, so I would like to send a simple read command without sending the command register as well.

Would that be fine or would the state machine not work if I do not write the control byte first?

Thanks,

SunSet

  • 0
    TI__Mastermind 24476 points

    Hello Sunset,

    Here are the default values of the configuration register as seen in the datasheet:

    This means the default is all bits are setup as inputs and if you do a read it will determine the state of the device.  Note, if the input doesn't have a pull-up or pull-down that you could have some excessive current draw due to the fact you are leaving a CMOS input floating. 

    -Francis Houde

  • 0 in reply to fhoude
    TI__Genius 14125 points

    Hello Francis,

    the register of interest is the control register (Figure 19) that contains the pointer of the register that will be read after the following read.

    For this there is no default value.

    Knowing this may help.

    Indeed if I know that is 0x00, this means that I could read the port directly without sending the 0x00 pointer (command)  first.

    Thanks,

    SunSet