Rainbow Electronics MAX66000 - Manual (Page 18)

MAX66000
ISO/IEC 14443 Type B-Compliant
64-Bit UID
18 ______________________________________________________________________________________
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.