AT88RF1354_09 Datasheet, PDF (28/48 Pages) ATMEL Corporation – 13.56 MHz Type B RF Reader Specification

Figure A-6. Location of the two CRC_B bytes within a frame.
SOF
K Data Bytes
CRC1
CRC2
EOF
The CRC_B polynomial is defined in ISO/IEC 14443 and ISO/IEC 13239 as x¹⁶ + x¹² + x⁵ + x⁰. This is a hex polynomial
of $1021. The initial value of the register used for the CRC_B calculation is all ones ($FFFF). When receiving
information from the PICC, the AT88RF1354 reader automatically computes the CRC on the incoming command, data,
and CRC bytes. When transmitting data the AT88RF1354 reader automatically computes the CRC on the outgoing
data packet, and inserts it prior to the end of frame. Any CRC error detected by AT88RF1354 is reported to the host
microcontroller.
A.8.
Modulation Index
The Modulation Index of the PCD generated magnetic field is measured by placing a calibration coil or wire loop near
the PCD antenna. Connect this loop to a high impedance oscilloscope probe and measure the amplitude modulation
(ASK) waveform as shown in Figure A-7. The PCD amplitude Modulation Index is defined in ISO/IEC 14443 part 2 as
the M.I. = (A - B) / (A + B). For Type B operation the PCD modulation index is required to be between 8 % and 14 %.
If the PCD modulation is less than 8 % then the PICC receiver will not successfully decode the transmissions.
Excessive modulation reduces the power available to the PICC and may cause it to reset.
Figure A-7. Measurement of the PCD Amplitude Modulation Index.
B
A
Modulation Index =
(A - B)
(A + B)
Modulation Depth =
B
A
A = Unmodulated Signal Amplitude
where:
B = Modulated Signal Amplitude
A.9.
Magnetic Field Strength
ISO/IEC 14443 part 2 defines the minimum and maximum operating magnetic field strength as Hmin and Hmax. A
credit card sized (ID-1) PICC is required to operate at all magnetic field strengths between Hmin = 1.5 A/m rms and
Hmax = 7.5 A/m rms. The PCD is not allowed to generate magnetic fields in excess of Hmax = 7.5 A/m rms. The PICC
is not required to function outside the operating envelope defined by Hmin and Hmax.
The magnetic field strength requirements of ISO/IEC 14443 part 2 apply only to systems utilizing ID-1 size PICCs,
which have an antenna area of approximately 3000 square millimeters. The magnetic field strength required to operate
28 13.56 MHz Type B RF Reader Specification
8547B–RFID–3/09