8 bits Header check sequence
The transmitter shall calculate the HCS value for the content
of the header excluding the HCS field, and insert the result
into the HCS field which is the last byte of the header). It
shall be the remainder of the division (Modulo 2) by the
generator polynomial g(D = D8 + D2 + D + 1) of the
polynomial D8 multiplied by the content of the header
excluding the HCS field. (Example: [Length=0x447, UCS=0,QPA=0, EC=1, EKS=01, Type=11001, FID=010;
the resulting GMH=0x88E5CB and the HCS calculated over it = 0x27]).