CRX14_05 Datasheet, PDF (25/40 Pages) STMicroelectronics – Low Cost ISO14443 type-B Contactless Coupler Chip with Anti-Collision, CRC Management and Anti-Clone Function

CRX14
Transmission Frame
The Request Frame transmission must be fol-
lowed by a minimum delay, t₀ (see Table 13.), in
which no ASK or BPSK modulation occurs, before
the Answer Frame can be transmitted. t₀ is the
minimum time required by the CRX14 to switch
from transmission mode to reception mode, and
should be inserted after each frame. After t₀, the
13.56MHz carrier frequency is modulated by the
PICC at 847kHz for a minimum time of t₁ (see Ta-
ble 13.) to allow the CRX14 to synchronize. After
t₁, the first phase transition generated by the PICC
represents the start bit (‘0’) of the Answer SOF (or
the start bit ‘0’ of the first data character in non
SOF/EOF mode).
Figure 27. Example of a Complete Transmission Frame
Sent by
the CRX14
SOF
12 bits
at 106Kb/s
Cmd
10 bits
Data
10 bits
tDR
CRC
10 bits
Case of Answer Frame with SOF & EOF
Sent by the PICC
CRC
10 bits
EOF
10 bits
fs = 847.5kHz
Sync
SOF
Data CRC CRC EOF
t0
t1
64/fs Min 80/fs Min
tWDG
12 or 13
bits
10 bits
10 bits
10 bits
12 or 13
bits
Case of Answer Frame without SOF & EOF
Output Data Transfer using ASK Modulation
Sync
Data Data Data CRC CRC
t0
t1
64/fs Min 80/fs Min
tWDG
10 bits
10 bits
10 bits
10 bits
10 bits
Input Data Transfer using 847kHz BPSK Modulation
ai09255
CRC
The 16-bit CRC used by the CRX14 follows the
ISO14443 type B recommendation. For further in-
formation, please see APPENDIX A., page 38.
The two CRC Bytes are present in all Request and
Answer Frames, just before the EOF. The CRC is
calculated on all the Bytes between the SOF and
the CRC Bytes.
Upon transmission of a Request from the CRX14,
the PICC verifies that the CRC value is valid. If it is
invalid, it discards the frame and does not answer
the CRX14.
Upon reception of an Answer from the PICC, the
CRX14 verifies that the CRC value is valid. If it is
invalid, it stores the value FFh in the Input/Output
Frame Register.
The CRC is transmitted Least Significant Byte first.
Each Byte is transmitted Least Significant Bit first.
Figure 28. CRC Transmission Rules
LSBit
LSByte
MSBit LSBit
MSByte
MSBit
CRC 16 (8 bits)
CRC 16 (8 bits)
ai09256
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