Forum Post: RE: Some doubts on SLAA512--《Using TI Technology to Simplify Bluetooth Pairing Via NFC》

These bytes you are asking about are called the Protocol Control Bytes (PCB) bytes and are from ISO14443-4 standard. The NFC Forum neglected to add those into any of their documents, but they are required to indicate if the data transmission is an I-Block, an R-Block or an S-Block.