SR176_07 Datasheet, PDF (8/35 Pages) STMicroelectronics – 13.56 MHz, 176-bit short range contactless user EEPROM with 64-bit Unique ID

Data transfer
3
Data transfer
SR176
3.1
Input data transfer from the Reader to the SR176 (request
frame)
The reader that accesses the SR176 must generate a 13.56 MHz sinusoidal carrier wave on
its antenna, with enough energy to “tele-power” the SR176 device. The energy received on
the SR176 antenna is transformed to a power supply voltage by a regulator, and to data bits
through the ASK demodulator. To decode correctly the information sent to the SR176, the
reader must use a 10% amplitude modulation of the 13.56 MHz wave, as represented
(though not to scale) in Figure 3. The data transfer rate is 106 Kbit/second.
Figure 3. Received wave using ASK modulation
Data Bit Transmit
to the SR176
13.5MHz 10% ASK
Modulation Generated
by the Reader
One bit time is 1/106kHz
AI09058
3.2
Character transmission format for request frame
Data Bytes are transmitted and received by the SR176 as 10-bit characters, as shown in
Figure 4, with the least significant bit (b₀) transmitted first. These characters, with the
addition of the Start Of Frame (SOF) and the End Of Frame (EOF), are grouped to form a
Command Frame as shown in Figure 10. The frame includes an SOF, instructions,
addresses, data, a CRC and an EOF as defined by ISO 14443-3 Type B. If an error is
detected during the data transfer, no error frame is generated by the SR176, and the
instruction is not executed.
Each bit duration is referred to as an ETU (Elementary Time Unit). One ETU is equal to
9.44 µs (1/106 kHz).
3.3
Request start of frame
The SOF, as shown in Figure 5, consists of:
● one falling edge
● followed by 10 ETUs at logic 0
● followed by one single rising edge
● followed by at least 2 ETUs (but no more than 3 ETUs) at logic 1.
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