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,
Matthias