out rmx is a four input eight bit wide multiplexer 178 which supplies input to the ram data bus its inputs are fdc out m3 out cer bus and the external microcontroller data bus sk is a five bit register 175 which holds the address of the low order coefficient of the u03c3 sup k polynomial in the ram sk can be preset to 0eh or loaded from sn out sk can be decremented sn is a five bit register 171 which holds the address of the low order coefficient of the u03c3 sup n polynomial in the ram sn can be preset to 1fh or loaded from sk out fig1 is a block diagram of the crc residue adjuster cra which is a lfsr implementing h x the reciprocal of the reed solomon generator polynomial gc x for the ansi iso standard crc code cra comprises four eight bit registers 185 188 denoted c0 c1 c2 and c3 the cm computation circuit 183 described below a two input eight bit wide multiplexer 184 deonted mx a two input eight bit wide exclusive or circuit 181 denoted eo and an eight bit gating circuit 182 denoted cg the output of c3 is cra out cra in and cra out are applied to the inputs of eo eo out is applied to cg in cg out c2 out c1 out and c0 out are.