NFC and the CR95HF

RE: NFC and the CR95HF

T IJ — Tue, 26 May 2020 07:38:29 GMT

I've done a lot of studying in the Digital Protocol Technical Specification but one thing is missing or I just don't see it. That is setting up a write sequence to the tag.

https://its-wiki.no/images/3/3b/NFC_forum_digital_protocol.pdf

I can only get my hands on version 1, as every other document on the NFC forum is behind a paywall.

I have downloaded the NFCForum-TS-Type-4-Tag_2.0 from Google (version 2.0 is probably outdated as well) http://apps4android.org/nfc-specifications/NFCForum-TS-Type-4-Tag_2.0.pdf

I follow the appendix C.3 Write NDEF file to clear the reccord but it doesn't seem to work as the only response I get is equal to invalid tag or timeout.

I'm sending the following data: 00 04 0C 02 00 D6 00 00 05 00 03 D0 00 00 28

The response I get is this : 80 07 F2 10 99 41 08 00 00

What I should expect the device to return is 90 00 but im not getting it.

RE: NFC and the CR95HF

Michal — Fri, 22 May 2020 21:44:07 GMT

Proszę bardzo ;)

Great that I could help!

Answering your question, the NFC solution in Nordic is based on the NFC Forum specs, so to answer you original question I had to look up there (Digital Protocol Technical Specification v. 2.2). There you have everything defined - frames structures, types, every bit is explained. This information is also there in the ISO/IEC 14443-3 specs.

If you don't have access to those, most of the relevant information can be also found in the Nordic documentation:

collision resolution and general NFC-A information: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52832.ps.v1.1/nfc.html?cp=4_2_0_41#concept_kmr_nxj_1s (this part is implemented in the HW)
Type 2 and Type 4 Tag and NDEF: https://infocenter.nordicsemi.com/topic/sdk_nrf5_v16.0.0/library_nfc.html?cp=7_1_3_33

Kind regards,

Michał

RE: NFC and the CR95HF

T IJ — Wed, 20 May 2020 09:53:40 GMT

You... You... You are awesome. If it wasn't for Covid-19 I'd give you a hug.

I've got it working and now I can read out my tag properly. Thank you for ending my week of struggling to get the damn chip operational.

The double size UID was the case I had indeed.

I continued using the datasheets reference on reading out the type 4 tag but instead of having a single size UID I implemented the double size UID. This method is select1 anticol1 and select2 anticol2.

After this the chip accepted the RATS command and reading out the rest was accepted.

Here is an image of me reading out my nRF tag.

One question tho, all this information you'd posted. Is this something you knew or did you read it somewhere because I am unable to find any information on what these numbers actually mean.

I can continue being busy with deciphering the rest of the data around it.

Kind regards and,

Dziękuję Ci Michał

RE: NFC and the CR95HF

Michal — Mon, 18 May 2020 16:26:08 GMT

Hi,

Responding briefly to your questions/concerns:

80 05 4400 280000 is correct, value '4400' is a SENS_RES frame which the tag transmits as a response to SENS_REQ (REQ-A). The value '4' instead of the "expected" '0' means the tag uses a double-size UID (7 bytes). Refer to the NFC Forum "Digital Protocol Specification" section 6.6.3.
80 08 885FAF 91E9 280000 is also correct - like you suggested, the tag has a different UID than what is shown in the example from the datasheet. BTW, byte '5F' is a manufacturer ID
RATS command - yes it is required to activate the Type 4 Tag, and the tag normally should respond to this command - if it is transmitted correctly from the reader.
PPS command is not supported by the SDK Type 4 Tag library, and is not required by the NFC Forum specs - you should be able to read and write the tag without using this command

I would suggest that you go to the nRF Connect SDK, even just for reference (you don't have to migrate there with you project). There you can find a reference NFC reader implementation which uses a chip from the ST25 family (as Nordic doesn't provide the NFC Reader/Writer HW solution), see: http://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/include/st25r3911b_nfc.html. You can find the source code at: https://github.com/NordicPlayground/fw-nrfconnect-nrf/tree/master/lib/st25r3911b

Here you can find implementations of the required protocols (for supporting T4T) also for the Reader/Writer side: github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/subsys/nfc/t4t/

Best regards,

Michał