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Original question:

CDCE913/CDCEL913 Address for I2C

CDCE925: CDCE295 / CDCE913 on same I2C bus

Chris Burrell83
Prodigy 110 points
Part Number: CDCE925
Other Parts Discussed in Thread: CDCE913, , CDCE937, CDCE949

Hello,

I am trying to understand the addressing scheme for CDCE925 / CDCE913.

If I have a CDCE925 and CDCE913 on the same I2C bus, how do I take advantage of the A1 / A0 bits?

It looks like, from the data sheet, that the top 5 bits of the CDCE913 and CDCE925 address bits are the same, so if you can change the lower two bits you could potentially make the CDCE913 and CDCE925 the same address - making it impossible to distinguish between the two.  Likewise, the CDCE937 and CDCE949 share the same top 5 address bits yet appear to have the bottom 2 address bits be programmable.

It also looks like the addresses given are the default ones which does make them unique.

Is it intended that the A1 / A0 bits are programmed outside the system, off the PCB, if the system has more than one CDCE chip?

An explanation of how the A1 / A0 bits are intended to be used would be most appreciated.

  • 0
    Prodigy 110 points

    If anyone else is interested I chased this one out.

    The data sheets for the different devices show that the default values for the A1 and A0 bits match the data-sheet-given address values:

    CDCE913 = 11001xx where xx is 01 by default

    CDCE925 = 11001xx where xx is 00 by default

    CDCE937 = 11011xx where xx is 01 by default

    CDCE949 = 11011xx where xx is 00 by default

    So, if you have two of the same device on the I2C bus at the same time, without programming them outside the PCB (or building in some way of isolating them) then there is no way to access each device independantly.  Equally, you can program a CDCE925 to appear as a CDCE913 default value but then you are stuck, because they both will acknowledge the same address request.

  • 0 in reply to Chris Burrell83
    TI__Genius 12705 points

    Hello Chris,

    Thank you for the follow up.

    To have multiple devices of the same type on the same board you would need to sequence power on the devices to configure a different I2C address from default. Alternatively the configurations could be loaded into EEPROM prior to assembly.

    Kind Regards,

    Liam