Programming ST25TA with NFC Tap app

[DStei.5]

Dear community,

for my project it is necessary to write a text on a ST25TA NFC tag and lock it afterwards permanently.

For this I use the ST25 NFC Tap app (Android & iOS), but the interface is hard to understand without any guides.

Is there an expert or a manual which can show me how to lock this NFC tag with the app permanently, so that NDEF text can be read by anyone and the NFC tag can't be manipulated?

When I choose option: "Write lock permanently" (Screenshot 2), a pop-up wants me to enter a password in hex (Screenshot 1). If I do nothing and just press "OK" the NFC tag seems to be locked. I am safe with this way, so that the message can't be changed or the tag influenced by others?

Best regards

David

[Olivier L]

Hi David,

Your tag displays "Write access status = 0xFF = Not authorized" which means that this tag is already locked permanently and cannot be written anymore (was it done intentionaly or by mistake?).

If you try to write to it or to change the "write lock" flag, it will keep asking for a password but in fact the write is impossible so the action can never succeed. This is normal.

For your information, if you had used the "Write lock" button, you would see "Write access status = 0x80 = Locked by password". In that case, the password can be presented to allow a write action.

Do you have another tag to try again?

For your information, the read lock and the write lock features are independant. If you keep the default password (with only zeros) someone may take your tag and lock the read feature (preventing the reading of the tag). I suggest to change the read password to avoid this issue.

So the procedure will be:

• write some NDEF content
• Change the read password
• Click on "Write lock permanently".

That should do what you want.

Here is the product Datasheet if you want to read some information about the read lock and write lock features:

https://www.st.com/en/nfc/st25ta64k.html

Regards

Olivier

[DStei.5]

Hello Oliver,

thanks for your help!

Yes, I locked the tag intentionaly. Good to know, that the asking for a password in "permanent write lock", is normal.

I've tried your recommendation, it is working, but everyone has to know the password this way.

But if I click on "permanent write lock" first, and the status of the tag gets:

read access = 0x00= not locked

write access = 0xFF= not authorized

if I then want to setup a read password

Android: shows me "Error while updating the tag!"

iOS: can't find the option, but I guess it isn't possible as in android, so I think I would be safe with this way too against possible sabotage, am I right?

Best regards

David

[Olivier L · Accepted solution]

Hello David,

I have done some tests on a ST25TA64K. I see that I have told you a mistake. The change of the read password is not needed because, once the write access locked permanently, the "read lock" cannot be changed anymore. In the datasheet, in "7.4 Locking an NDEF file", it is said that the Write password is needed to lock an NDEF file. In your case, it is no more possible to present the write password successfully because it is locked permanently.

So the "write lock permanently" is enough to avoid a sabotage.

Best regards

Olivier

[DStei.5]

Ahh great, thanks for your fast help and knowledge Olivier!