Crc generation – Rainbow Electronics MAX66000 User Manual
Page 18
MAX66000
ISO/IEC 14443 Type B-Compliant
64-Bit UID
18
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Figure 31. 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 ISO/IEC 14443 standard uses a 16-bit CRC, gener-
ated according to the CRC-16-CCITT polynomial func-
tion: X
16
+ X
12
+ X
5
+ 1 (Figure 31). This CRC is used
for error detection in request and response data pack-
ets 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.