The problem with cipher reading data from FIFO

[SwargSgt]

Hello all.

I use ST25R3911B-DISCO and dynamic tag ST25dv04k

When reading data from FIFO come bytes with a redundant cipher.

Suppose the code is presented as custom manchester code:

• 10 - 0, (two bits in recived bytes - bit result)
• 01 - 1,
• 00 - 0,
• 11 - 1.

After that, you need to perform a cyclic shift to the right by 3.

It all works with the exception of some bytes.

For example: in fact (in tag buffer) - 0xAA. Recived 0x3333, after decryption - 0xAA. All ok

But it happens: in fact - 0xCC. Recived 0xb3b4, after decryption - 0xCA.

Where can I read more about this cipher?

Or what am I doing wrong?

[Ulysses HERNIOSUS]

Hi,

actually this is not a cipher but the bit coding VICC->VCD. It is Manchester coding and e.g. defined in ISO/IEC15693-3 or NFC Forum Digital specs.

ST25R3911B does not perform ISO15693 bit coding/decoding internally.

If you experience issues, then you should start off by looking at the SOF pattern and see why you experience a shift here. Possibly the timings (MRT of 3911B is not set appropriately).

Does the same happen using the ST25R3911B-DISCO GUI/firmware? Which version? If so then please give details how to reproduce this. Otherwise the firmware sources are available and are working.

Regards, Ulysses