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LMH1297: I2C Communications Protocol Confusion Regarding RAW & RAR

David Fatzer
Prodigy 20 points
Part Number: LMH1297

Tool/software:

We are attempting to set the page select register to point to the CTLE/CDR page by writing a 0x04 to register 0xFF.  When we do an I2C read the value returned is 0x03. The LMH1297 device address is 0x2F. Please review the screen capture below and let us know what we are doing wrong.  This is rather urgent.  Thanks, David Fatzer. Leonardo DRS.

  • 0
    TI__Genius 13726 points

    Hi David, 

    Is this issue happening with our sigcon GUI, or is this happening on the system? If it is happening on the system, could you try if the same issue persists when using our GUI?
    What is the external pull-up resistance on SCL and SDA? Does it pull to VIN?
    In addition, have you taken a look at this FAQ?
    If you could, could you provide us your schematic to see if there is anything wrong in the chip configuration?
    Please let me know. 

    Best,
    J 

  • 0
    Guru 317280 points

    The last parameter of the RAW command is a bit mask that indicates which part of the register is to be changed. It is not a data byte and must not show up on the bus.

    Just write the value 0x04, by itself. If you actually want to do the bit masking, then you would have to do a read from register 0xFF first.