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#1 2020-04-17 23:14:30

unfrozen
Contributor
Registered: 2020-04-16
Posts: 2

NTAG213: Does NAK force state to IDLE/HALT?

I am having pretty good luck with my NTAG213 tags. I can read and write, get the authenticity signature, set ASCII mirroring, and enable the read counter.

But while doing the READ_CNT command BEFORE I enabled the counter, the tag would just stop talking, until the next session. AFTER I enable the read counter, the READ_CNT and ASCII mirroring work fine.

It seems that until I enable the read counter, the tag responds to READ_CNT with NAK and goes to sleep. So far, this is the only time I am getting a NAK. So I try a write above the user memory limit, and also get a NAK and the tag goes to sleep.

The NTAG213 datasheet (Rev. 3.2 — 2 June 2015 265332) says nothing beyond: (Page 8, figure 4)

Remark: In all states, the command interpreter returns to the idle state on receipt of an unexpected command. If the IC was previously in the HALT state, it returns to that state."

I have searched every mention of NAK, and there is nothing saying a NAK on a valid command will cause the tag to go to IDLE or HALT.

I have only found one discussion of this (with a great deal of trying):
https://www.mifare.net/support/forum/to … t-ev1-tag/

An expert notice me that in a case of failure the tag goes into the HALT state which can be interpreted as “end of communication” ...

If you look to page 8 of the Ultralight EV1 datasheet you will find the sate diagram. If an error, unexpected command or other failure occurs, the state machine goes into HALT or IDLE state. For an ISO/IEC 14443-3 compliant tag there is no other choice.

I have 14443-3 second draft, and I don't see anywhere that it gives "no other choice".

And page 8 of the Ultralight EV1 datasheet does NOT say that. It says,

Remark: In all states, the command interpreter returns to the idle state on receipt of an unexpected command. If the IC was previously in the HALT state, it returns to that state.

It says nothing of an "error" or "other failure".

The obvious thing to do is to just assume that a NAK requires a new tag select sequence. But I would really want to KNOW FOR A FACT exactly what is going on.

Does anyone have experience with NXP, and especially NTAG, handling of NAK?

Thanks!

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