CRX14_05 Datasheet, PDF (23/40 Pages) STMicroelectronics – Low Cost ISO14443 type-B Contactless Coupler Chip with Anti-Collision, CRC Management and Anti-Clone Function

CRX14
Input RF Data Transfer from the PICC to the
CRX14 (Answer Frame)
The CRX14 uses the ISO14443 type-B retro-mod-
ulation scheme which is demodulated and decod-
ed by the RF_IN circuitry.
The modulation is obtained by modifying the PICC
current consumption (load modulation). This load
modulation induces an H-field variation, by cou-
pling, that is detected by the CRX14 RF_IN input as
a voltage variation on the antenna. The RF_IN input
demodulates this variation and decodes the infor-
mation received from the PICC.
Data must be transmitted using a 847kHz, BPSK
modulated sub-carrier frequency, f_S, as shown in
Figure 24., and as specified in ISO14443 type-B.
In BPSK, all data state transitions (from ‘0’ to ‘1’ or
from ‘1’ to ‘0’) are encoded by phase shift keying
the sub-carrier.
Figure 24. Wave Received using BPSK Sub-carrier Modulation
1/106kHz
PICC data bit to be transmitted
to the CRX14.
1/847kHz
VRFIN
phase shift
847kHz BPSK, resulting signal
generated by the PICC for the
load modulation.
V_RET
VOFFSET
VDYN
Load modulation effect on
the H-Field received on the
CRX14 RFIN input pad
t
ai09253
Transmission Format of Answer Frame
Characters
The PICC should use the same character format
as that used for output data transfer (see Figure
21.).
An Answer Frame includes the SOF, data, CRC
and the EOF, as illustrated in Figure 27.. The data
transfer rate is 106 kbit/s.
The CRX14 will also accept Answer Frames that
do not contain the SOF and EOF delimiters, pro-
vided that these Frames are correctly set in the
Parameter Register. (See Figure 27.).
23/40