Some Androids requires manually sending RATS and adding block numbers in transceive() for NfcA tags (ISO 14443-4A)

Question

When reading NfcA tags, I found that some Android models (e.g. Samsung S8) requires me to explicitly send out RATS before SELECT and to send any I-blocks, the block number (2/3) has to be inserted explicitly at the first byte of the command and the block number will also appear in the 1st byte of the response, i.e.

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Code snippet 1

byte[] response = nfca.transceive(Utils.getBytes("E0 80")) ; //RATS
response = nfca.transceive(Utils.getBytes("02 00 A4 04 00 07 A0 00 00 05 50 00 11")) ; //SELECT, response =02...

Results of running code snippet 1 on LG-LM-Q710 Results of running code snippet 1 on SM-G9500

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However, for some (e.g. LG Q Stylus+ ), neither are necessary, which is the right abstraction I expect:

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Code snippet 2

byte[] response = nfca.transceive(Utils.getBytes("00 A4 04 00 07 A0 00 00 05 50 00 11")) ; //SELECT

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Why is the ISO 14443-4A protocol differently abstracted? Is this due to different NFC stacks or NFC controller? How could I detect which one to use?

Answer 1

NfcA on Android only provides access to ISO 14443-3A

For ISO 14443-4A you should be using IsoDep class

You don't specify the exact make and model of the Tag, so it is difficult to tell how well it complies to the NFC standards (some don't fully comply and some types of card are only optionally supported on Android)