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Original question:

LMX2820: SPI protocol details needed

LMX2820: chip ID

Paul Burkacki
Prodigy 70 points

Part Number: LMX2820
Other Parts Discussed in Thread: LMX2594

Hello,

I would like to programmatically determine whether or not the PLL my application is communicating with is an LMX2820.  In the past, when I worked with a different PLL, I was able to retrieve the ID of that chip by reading a specific register.  Is this possible with the LMX2820?  I read through the datasheet but I have not found any registers which would provide such data.

Any help is appreciated.

Regards,

Paul

  • 0
    TI__Guru** 114670 points

    Hi Paul,

    There is no device ID in the chip, you may use R59 as the ID, upon a Vcc power up or a RESET, the value is 0x1388.

  • 0
    Prodigy 70 points

    Hi Noel,

    thank you for your reply. I am still missing something.  When I first started to look at the details of SPI communications for LMX2820, I actually had to review the datasheet for LMX2594.  This is because the datasheet for LMX2820 did not have any details regarding SPI.  I found a post on a TI forum which suggested that the LMX2594 datasheet should be referenced to get this information.  Continuing to look at the datasheet for the LMX2594 (LMX2594, page 51), R59 seems to be set to all 0s except for the bit 0 which is LD_TYPE.  That value is listed as 1 after reset.

    But again, this is from the datasheet for LMX2594.  Is it possible that R59 for LMX2820 has different value after reset?

    Regards,

    Paul

  • +1 in reply to Paul Burkacki
    TI__Guru** 114670 points

    Hi Paul,

    both device have the same SPI format and structure (1-bit R/W, 7-bit address, 16-bit data), but the register values are different. 

    LMX2820 register maps is available here: https://www.ti.com/lit/pdf/snau251

  • 0 in reply to Noel Fung
    Prodigy 70 points

    Hi Noel,

    thanks for the link.  I was able to get the register value.  Thank you for your help.

    Regards,

    Paul