CR14 datasheet(28/46 Pages) STMICROELECTRONICS

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6 CR14 ISO14443 type-B Radio Frequency data transfer

CR14

28/46

6.4

Request End Of Frame

The End Of Frame (EOF) shown in Figure 22 consists of:

●

a falling edge,

●

followed by ten Elementary Time Units (ETU) containing each a logical ‘0’,

●

followed by a single rising edge.

Figure 22. Request End Of Frame

6.5

Input RF Data Transfer from the PICC to the CR14 (Answer

Frame)

The CR14 uses the ISO14443 type-B retro-modulation scheme which is demodulated and

decoded by the RFIN 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 CR14 RFIN

input as a voltage variation on the antenna. The RFIN input demodulates this variation and

decodes the information received from the PICC.

Data must be transmitted using a 847kHz, BPSK modulated sub-carrier frequency, fS, 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

ETU

0000000000

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VDYN

VRFIN

VOFFSET

1/106kHz

1/847kHz

phase shift

VRET

Load modulation effect on

the H-Field received on the

CR14 RFIN input pad

PICC data bit to be transmitted

to the CR14.

847kHz BPSK, resulting signal

generated by the PICC for the

load modulation.

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