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Transport aspects 2

CRC-6

6
Table VI.4 illustrates example logic equations for a parallel implementation of the CRC-6 using the g(x) = x
2
3
+ x + x + 1 polynomial over the JC1-JC2. An "X" in a column of the table indicates that the message bit of
that row is an input to the Exclusive-OR equation for calculating the CRC bit of that row. JC1.C1 corresponds
to bit 3 of the first mapping overhead octet (JC1), JC1.C2 corresponds to bit 4 of the first mapping overhead
octet, etc. After computation, CRC bits crc1 to crc6 are inserted into the JC3 octet with crc1 occupying bit 3
and crc6 the LSB of the octet. (See Figure 20-7)

Table VI.4 – Parallel logic equations for the CRC-6 implementation

CRC checksum bits
Mapping overhead
bits crc1 crc2 crc3 crc4 crc5 crc6

JC1.C1 X X X
JC1.C2 X X X
JC1.C3 X X X X X
JC1.C4 X X X X X
JC1.C5 X X X
JC1.C6 X X X
JC2.C7 X X X

JC2.C8 X X X
JC2.C9 X X X
JC2.C10 X X X
JC2.II X X X
JC2.DI X X X

1291