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AFE8000EVM: LMK04828 frequency is not properly set.

James Bae
Prodigy 40 points
Part Number: AFE8000EVM
Other Parts Discussed in Thread: AFE8000,

Hello,

I am trying to bring up the AFE8000 EVM.
My environment is below.

FPGA Board : ZCU102
Connector used : HPC1
SW : Latte (AFE80xxCat)
10MHz ref : not connected.

To quick review, I first loaded an excel file in Latte.
The file name is "AFE80xx_SystemParameters_2949p12_8847p36_RX_245p76p64_TXFB_491p52.xlsx"
In this configuration file, Fref is 491.52MHz. After I checked the real frequency value
(measured it by connecting two wires on resistors R326 / R331 in the schematic),
frequency seems not to properly set. The measured value was about 500MHz.

Also, in the top page of AFE80xx sw, when I changed the FPGA input clock value
250 to 245.76MHz the value is not changed.
(measured the frequency value by connecting two wires on resistors C339 / C340 in the schematic)
125MHz is well applied and changed.

Here, what I want to know is that "Can't I change the frequency value to the multiples of 122.88MHz in the latte software?"
Do I have to control LMK using fpga through the FMC connector?

Thanks in advance.

  • +1
    TI__Genius 17781 points

    Hi James,

    The reason that you are seeing these issues is because the AFE8000EVM does not have a 122.88MHz crystal on board, it is a 100MHz crystal. The configuration file that you should be using as a reference should be called 'AFE8000_SampleConfig' and will configure the LMK to output the 500MHz reference to the AFE. 

    If you would like to use a Fref of 491.52MHz you would have to provide an external reference to the LMK and divide it down for the AFE and FPGA clocks. To do this you can turn off PLL Enable and then change the LMK Input Clock to 983.04MHz, this would mean that you would need to provide a 983.04MHz clock to the LMK_CLK_IN connector, J18.

    Regards,

    David Chaparro