Hi,
in ISO/14443, Anticollsion frames are bit oriented. Therefore, a non integer amount of bytes can be received (see case SPLIT BYTE in ISO14443-3 standard). In that case a 0x90 Response Code is returned.
0x90 response code is also returned when a type 2 tag sends a 4-bits ACK or NACK reply.
0x90 response code can also be returned when a tag sends a partial answer (RF loss or power loss on tag side).
For Anticollision frames, the total length (part 1 from the PCD + part 2 from the VICC) shall be 56. As per NFC Forum Digital Protocol Technical Specification 2.0 requirement 6.7.2.12, invalid part 2 length shall be treated as a syntax error. This is the likely case here (seem the tag started to sent the SAK and 5 bits of the CRC before stopping replying).
When a 0x90 reply is received, you can retrieve the number of valid bits of the last data byte thanks to the 3 additional bytes (e.g. 25 00 00 --> 5 valid bits). See ST25R95 datasheet table 17. In case of Anticollision frame, you can then compute the length of the part 2 and behave accordingly.
For your information, X-CUBE-NFC3 v2.0.0 fully manage 0x90 response code. Do you use your own driver or the X-CUBE-NFC3 v2.0.0 library?
Rgds
BT
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