ST25TB02K datasheet(7/47 Pages) STMICROELECTRONICS

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3.2

Output data transfer from to reader ST25TB02K (answer frame)

The data bits issued by the ST25TB02K use back-scattering. Back-scattering is obtained by modifying the

ST25TB02K current consumption at the antenna (load modulation). The load modulation causes a variation at the

reader antenna by inductive coupling. With appropriate detector circuitry, the reader is able to pick up information

from the ST25TB02K. To improve load-modulation detection, data is transmitted using a BPSK encoded, 847 kHz

subcarrier frequency ƒs as shown in Figure 7, and as specified in the ISO 14443-2 Type B standard.

Figure 7. Wave transmitted using BPSK subcarrier modulation

Data Bit to be Transmitted

to the Reader

847kHz BPSK Modulation

Generated by the ST25TBxxx

BPSK Modulation at 847kHz

During a One-bit Data Transfer Time (1/106kHz)

3.2.1

Character transmission format for answer frame

The character format is the same as for input data transfer (Figure 4). The transmitted frames are made up of

an SOF, data, a CRC and an EOF (Figure 10). As with an input data transfer, if an error occurs, the reader does

not issue an error code to the ST25TB02K, but it should be able to detect it and manage the situation. The data

transfer rate is 106 Kbits/second.

3.2.2

Answer start of frame

The SOF described in Figure 8 is composed of:

•

one falling edge,

•

followed by 10 ETUs at logic-0,

•

followed by 2 ETUs at logic-1.

Figure 8. Answer start of frame

ETU

b10

b11

ST25TB02K

Output data transfer from to reader ST25TB02K (answer frame)

DS11469 - Rev 7

page 7/47

ST25TB02K Datasheet(PDF) 7 Page - STMicroelectronics