SRI4K datasheet(11/45 Pages) STMICROELECTRONICS

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SRI4K

Data transfer

11/45

3.2

Output data transfer from the SRI4K to the reader (answer

frame)

The data bits issued by the SRI4K use retro-modulation. Retro-modulation is obtained by

modifying the SRI4K 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 SRI4K. 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

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 SRI4K, 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:

●

followed by 10 ETUs at logic-0

●

followed by 2 ETUs at logic-1

Figure 8.

Answer start of frame

AI10881

Data Bit to be Transmitted

to the Reader

847kHz BPSK Modulation

Generated by the SRI4K

BPSK Modulation at 847kHz

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

ai07665

ETU

b10

b11

0000000000

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