The value for the FIS type fields of all FISes has been selected to provide additional robustness. In minimally buffered operations that might not buffer a complete FIS, the state machines might begin acting on the received FIS type value prior to the ending CRC having been checked.
Because the FIS type value might be acted upon prior to the integrity of the complete FIS being checked against its ending CRC, the FIS type field values have been selected to maximize the Hamming distance between them.
FIS type value assignments are listed in Table: FIS Type Value Assignments.