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Transport aspects 2

Appendix VI

Parallel logic implementation of the CRC-9, CRC-8, CRC-5 and CRC-6
(This appendix does not form an integral part of this Recommendation.)

CRC-9

9
Table VI.1 illustrates example logic equations for a parallel implementation of the CRC-9 using the g(x) = x
2
3
+ x + x + 1 polynomial over the CnD fields of JC1, JC2, JC4 and JC5. 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. JC4.D1 corresponds to bit 2 of the JC4 mapping overhead octet, JC4.D2 corresponds to bit 3
of the JC4 octet, etc. (See Figure 20-7.) After computation, CRC bits crc1 to crc9 are inserted into the JC6
and JC3 octets with crc1 occupying bit 2 of the JC6 octet and crc9 occupying bit 2 of the JC3 octet.

Table VI.1 – Parallel logic equations for the CRC-9 implementation

Mapping CRC checksum bits
overhead bits
crc1 crc2 crc3 crc4 crc5 crc6 crc7 crc8 crc9
JC4.D1 X X X
JC4.D2 X X X
JC4.D3 X X X
JC4.D4 X X X
JC4.D5 X X X
JC4.D6 X X X
JC4.D7 X X X
JC1.D8 X X X

JC1.D9 X X X
JC5.D10 X X X X X
JC5.D11 X X X X X
JC5.D12 X X X X X
JC5.D13 X X X
JC5.D14 X X X
JC5.D15 X X X
JC5.D16 X X X
JC2.D17 X X X
JC2.D18 X X X

CRC-8

8
Table VI.2 illustrates example logic equations for a parallel implementation of the CRC-8 using the g(x) = x
3
2
+ 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 the first bit (MSB) of the first mapping overhead octet (JC1), JC1.C2 corresponds to bit 2 of the first
mapping overhead octet, etc. After computation, CRC bits crc1 to crc8 are inserted into the JC3 octet with
crc1 occupying MSB and crc8 the LSB of the octet.

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