ATR in Synchronous Transmission
The official reference defining the ATR in synchronous transmission is the ISO/IEC 7816-10 standard.
The ATR starts with a header of 32 bits organized into 4 bytes, denoted H1 thru H4. H1 codes the protocol (with '00' and 'FF' being invalid), H2 codes parameters of the protocol. Little more is standardized.
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