M16C6NK Datasheet, PDF (240/404 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/60 SERIES

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M16C/6N Group (M16C/6NK, M16C/6NM)
18. CRC Calculation
Setup procedure and CRC operation when generating CRC code "80C4h"
CRC operation performed by the M16C
CRC code: Remainder of a division in which the value written to the CRCIN register with its bit positions reversed is
divided by the generator polynomial
Generator polynomial: X⁶ +X¹² +X⁵[phone] 0001b)
Setting procedure
(1) Reverse the bit positions of the value "80C4h" by program in 1-byte unit.
"80h" → "01h", "C4h" → "23h"
b15
(2) Write 0000h (initial value)
b0
CRCD register
(3) Write 01h
b7
b15
1189h
b0
CRCIN register
Two cycles later, the CRC code for "80h," i.e.,
9188h, has its bit positions reversed to become
"1189h" which is stored in the CRCD register.
b0
CRCD register
(4) Write 23h
b7
b15
0A41h
b0
CRCIN register
Two cycles later, the CRC code for "80C4h," i.e.,
8250h, has its bit positions reversed to become
"0A41h" which is stored in the CRCD register.
b0
CRCD register
Details of CRC operation
As shown in (3) above, bit position of "01h" (00000001b) written to the CRCIN register is inversed and becomes "10000000b".
Add "1000 0000 0000 0000 0000 0000b", as "10000000b" plus 16 digits, to "0000 0000 0000 0000 0000 0000b", as
"0000 0000 0000 0000b" plus 8 digits as the default value of the CRCD register to perform the modulo-2 division.
1000 1000
1 0001 0000 0010 0001 1000 0000 0000 0000 0000 0000
1000 1000 0001 0000 1
Generator polynomial
1000 0001 0000 1000 0
1000 1000 0001 0000 1
1001 0001 1000 1000
CRC code
Data
Modulo-2 operation is
operation that complies
with the law given below.
0+0=0
0+1=1
1+0=1
1+1=0
-1 = 1
"0001 0001 1000 1001b (1189h)", the remainder "1001 0001 1000 1000b (9188h)" with inversed bit position, can be read
from the CRCD register.
When going on to (4) above, "23h (00100011b)" written in the CRCIN register is inversed and becomes "11000100b".
Add "1100 0100 0000 0000 0000 0000b", as "11000100b" plus 16 digits, to "1001 0001 1000 1000 0000 0000b", as
"1001 0001 1000 1000b" plus 8 digits as a remainder of (3) left in the CRCD register to perform the modulo-2 division.
"0000 1010 0100 0001b (0A41h)", the remainder with inversed bit position, can be read from CRCD register.
Figure 18.3 CRC Calculation
Rev.2.00 Nov 28, 2005 page 222 of 378
REJ09B0124-0200