Hello,
I already tested de Field detection feature and it works, I set up the FD_OFF as 00b and the FD_ON as 00b as well. Besides that, another configuration has to be made to be able to see the transition as mentioned in the datasheet. Please refer to chapter 8.4 Configurable Event Detection Pin, Fig 12. FD pin example circuit of the following document https://www.nxp.com/docs/en/data-sheet/NT3H2111_2211.pdf to configure FD pin circuit.
As you can see, I am detecting the transition from 1 to 0 in the oscilloscope when the reader's field is present.
Hardware:

High level:

Low level:

Best regards,
Ivan.
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