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ADF5901, ADF5904 readback chip id and reserved fields


During experiments I tryed to read back ADF5901 registers using DOUT line and by setting READBACK CONTROL code in R3. There are actually correct register values when ctl codes are 0b000001..0b001100 and 0b010110 for ADC readback. But I tryed to read back for ctl codes specified as 'RESERVED' in the datasheet. Suddently I got constant value 0x59010102 for ctl=27 that obviously looks like chip identification. For ADF5904 I found the same behaviour (0x59040002) for readback ctl=23.

There is nothing about this in available datasheets. The datasheet for ADF5901 is marked with 2017 year (too old?).

Could you point me to up to dated DS or reference manual with proper SPI protocol explaination because probably there are another possibilities except undocumented chip id readback.

Another thing unclear for me: what exactly means 'Reserved' parts for some registers shown in the datasheed as some value, not all-ones and not all-zeroes. For example, reserved DB19 in R1 has value 0 (Should I write always zero here? What will happen when I write one here?), DB17 in R2 has value 1 while all others are zeroes, and so on.

Thank you!

  • Hello,

    Yes it is possible to readback some of the other readback control code settings, but as you have noted some of these have been hidden from users since they were intended for our use only, or sometimes weren't fully operational, or were deemed unnecessary for normal operation. And some settings really aren't wired up to anything

    You are correct readback setting d27 will give the chip revision code.

    The last 13 readback settings (setting d51 to d63) are readbacks of registers 13/14/15/16 with various different masks.

    It's also possible to readback some basic VCO and frequency data but I am hesitant to release details of these on EngineerZone. if you send me an email I can possibly share some info so you can experiment. But these extra readback settings would be completely unsupported by us. 

    The ADF5901 datasheet on the web page is up to date. It is important to set reserved bits high/low as specified in the datasheet even if they are reserved since most of the reserved settings aren't "don't care" for this device and need to be set properly for correct device operation. 



  • Hi Alex, thank you for your reply!

    My email: a(at)

    Send me please details about reserved readbacks and reserved fields as much as it possible. I worry about R1 reserved part because it looks like related to calibration mechanism and I probably have an issue with calibration amplitude (chip power consumption doesn't depend on calibration code). So if you can explain reserved part of R1 or another way to access to internal ADC on diodes, I will appreciate.

    I understand that it's completely unsupportable information and want to use it only for debug purposes.

    Thank you!

  • No problem, I've emailed some information to you

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