mc9s08ac32 Freescale Semiconductor, Inc, mc9s08ac32 Datasheet - Page 132

• Manufacturer Part Number: mc9s08ac32
• Description: Hcs08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Chapter 8 Cyclic Redundancy Check (S08CRCV1)
8.4.1
The CRC polynomial 0x1021 (x
proposed by the ITU-T (formerly CCITT) committee.
Although the ITU-T recommendations are very clear about the polynomial to be used, 0x1021, they accept
variations in the way the polynomial is implemented:
Moreover, it is common to find circuits in literature slightly different from the one suggested by the
recommendations above, but also known as CRC-CCITT circuits (many variations require the message to
be augmented with zeros).
The circuit implemented in the CRC module is exactly the one suggested by the ITU-T V.41
recommendation, with an added flexibility of a programmable SEED. As in ITU-T V.41, no augmentation
is needed and the CRC result is not negated.
reference. Notice that these are ASCII string messages. For example, message “123456789” is encoded
with bytes 0x31 to 0x39 (see ASCII table).
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ITU-T V.41 implements the same circuit shown in
0x0000.
ITU-T T.30 and ITU-T X.25 implement the same circuit shown in
the final CRC result to be negated (one-complement operation). Also, they recommend a SEED =
0xFFFF.
ITU-T (CCITT) Recommendations and Expected CRC Results
1
A string of 256 upper case “A”
characters with no line breaks
A string of 256 upper case “A”
characters with no line breaks
A string of 256 upper case “A”
characters with no line breaks
One common variation of CRC-CCITT require the message to be
augmented with zeros and a SEED=0xFFFF. The CRC module will
give the same results of this alternative implementation when
SEED=0x1D0F and no message augmentation.
ASCII String Message
16
“123456789”
“123456789”
“123456789”
+ x
MC9S08AC60 Series Data Sheet, Rev. 2
Table 8-4. Expected CRC results
“A”
“A”
“A”
12
+ x
5
Table 8-4
+ 1) is popularly known as CRC-CCITT since it was initially
(initial CRC value)
shows some expected results that can be used as a
0x1d0f
0x1d0f
0x1d0f
0x0000
0x0000
0x0000
Figure
SEED
0xffff
0xffff
0xffff
1
1
1
8-2, but it recommends a SEED =
CRC result
0x58e5
0xb915
0x9479
0x31c3
0x29b1
0xe5cc
0xabe3
0xea0b
0xe938
Figure
8-2, but they recommend
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