SRIX4K Data transfer
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3.2 Output data transfer from the SRIX4K to the reader (answer
frame)
The data bits issued by the SRIX4K use retro-modulation. Retro-modulation is obtained by
modifying the SRIX4K 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 SRIX4K. To improve
load-modulation detection, data is transmitted using a BPSK encoded, 847 kHz subcarrier
frequency ƒ
s
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 SRIX4K, 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
Or
AI05730
Data Bit to be Transmitted
to the Reader
847kHz BPSK Modulation
Generated by the SRIX4K
BPSK Modulation at 847kHz
During a One-bit Data Transfer Time (1/106kHz)
ai07665
ETU
b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 b11
000000000011
