XTAL trimming on DW3000 chips


I currently try to measure the xtal frequency of my DW3000 chips. Application Note APS312 mentions many options of how to measure the frequency. I wanted to use the GPIO output mentioned in section as it is the most approachable for me right now.

In this section it states that 0x3 should be written to register 0x05:00. The DW3000 manual itself states that I should in fact not write 0x3 to the register:

011 – 111: Reserved. Do not select this value.

Ignoring this statement (btw quite odd to have those contradictory statements in official documents) I’ve written 0x3 to the register.

Measuring the frequency with an oscilloscope (don’t have a frequency analyzer at hand right now but just wanted to check if it works in general) I just get a steady output of 150mV - no sin wave or any AC in general tho.

My question is:
Should really 0x3 be written to this register? Has there anything else to be modified in the register (e.g. changing 0x5:08 to 0xFE to assign it as an output)? Or does anyone have experience with this method of calibration and can comment on it?

Kind regards

Hi Fhilb,

i have just tried this on a DWM3001CDK. After writing 0x3 to register 0x05:00 i can see a 31.25MHz signal on the GPIO0 pin.
I did not have to change 0x05:08, it is set to 0x1FF, changing to 0x1FE does not change the behaviour.

As to the wording in the user manual, 0x3 is ‘reserved’ for production testing and should not be set in normal operation.

Best regards,

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