Abridged data sheet, Crc generation – Rainbow Electronics MAX66040 User Manual
Page 23
MAX66040
ISO/IEC 14443 Type B-Compliant
Secure Memory
32
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ABRIDGED DATA SHEET
Figure 32. 8-Bit CRC Generator
1ST
STAGE
MSb
LSb
2ND
STAGE
3RD
STAGE
4TH
STAGE
7TH
STAGE
8TH
STAGE
6TH
STAGE
5TH
STAGE
X
0
X
1
X
2
X
3
X
4
POLYNOMIAL = X
8
+ X
5
+ X
4
+ 1
INPUT DATA
X
5
X
6
X
7
X
8
Figure 33. CRC-16-CCITT Generator
1ST
STAGE
MSb
LSb
2ND
STAGE
7TH
STAGE
8TH
STAGE
6TH
STAGE
X
0
X
1
3RD
STAGE
4TH
STAGE
5TH
STAGE
X
2
X
3
X
4
POLYNOMIAL = X
16
+ X
12
+ X
5
+ 1
INPUT DATA
X
5
X
6
11TH
STAGE
X
11
9TH
STAGE
10TH
STAGE
X
9
X
10
12TH
STAGE
15TH
STAGE
14TH
STAGE
13TH
STAGE
X
12
X
13
X
14
X
7
16TH
STAGE
X
16
X
15
X
8
CRC Generation
The MAX66040 uses two different types of CRCs. One
CRC is an 8-bit type. The equivalent polynomial func-
tion of this CRC is X
8
+ X
5
+ X
4
+ 1.
The other CRC is a 16-bit type, generated according to
the CRC-16-CCITT polynomial function: X
16
+ X
12
+
X
5
+ 1 (Figure 33). This CRC is used for error detection
in request and response data packets and is always
communicated in the inverted form. After all data bytes
are shifted into the CRC generator, the state of the 16
flip-flops is parallel-copied to a shift register and shifted
out for transmission with the LSb first. For more details
on this CRC, refer to ISO/IEC 14443-3, Annex B,
CRC_B encoding.