CRX14 ISO14443 type-B radio frequency data transfer CRX14
28/47 Doc ID 8880 Rev 4
6.5 Input RF data transfer from the PICC to the CRX14 (answer
frame)
The CRX14 uses the ISO14443 type-B retro-modulation scheme which is demodulated and
decoded 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 coupling, 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 information received from the PICC.
Data must be transmitted using a 847kHz, BPSK modulated sub-carrier frequency, f
S
, as
shown in Figure 23, 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 23. Wave received using BPSK sub-carrier modulation
6.6 Transmission format of answer frame characters
The PICC should use the same character format as that used for output data transfer (see
Figure 20).
An Answer Frame includes the SOF, data, CRC and the EOF, as illustrated in Figure 26. The
data transfer rate is 106 kbit/s.
The CRX14 will also accept Answer Frames that do not contain the SOF and EOF
delimiters, provided that these Frames are correctly set in the Parameter Register. (See
Figure 26).
V
DYN
V
RFIN
t
V
OFFSET
1/106kHz
1/847kHz
phase shift
V
RET
Load modulation effect on
the H-Field received on the
CRX14 RF
IN
input pad
PICC data bit to be transmitted
to the CRX14.
847kHz BPSK, resulting signal
generated by the PICC for the
load modulation.
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