SR176_07 Datasheet, PDF (11/35 Pages) STMicroelectronics – 13.56 MHz, 176-bit short range contactless user EEPROM with 64-bit Unique ID

SR176
Data transfer
3.9
Transmission frame
Between the Request and the Answer data transfer, there is a guard time without ASK and
BPSK modulation, for a minimum period of t₀ =128/f_S. This delay allows the reader to switch
from transmission to reception mode, and is applied after each frame. After t₀, the
13.56 MHz carrier frequency is modulated by the SR176 at 847.5 kHz for a period of
t₁ = 128/f_S, to allow the reader to synchronize. After t₁, the first phase transition generated
by the SR176 represent the start bit (‘0’) of the Answer SOF. After the falling edge of the
Answer EOF, the reader has to wait for the minimum delay, t₂, before sending a new
Request Frame to the SR176.
Figure 10. Example of a complete transmission frame
Sent by the
Reader
SOF
12
bits
Cmd
10
bits
at
106kb/s
Sent by the
SR176
Data
10
bits
CRC
10
bits
tDR
CRC
10
bits
EOF
10
bits
fS=847.5kHz
Sync SOF
12
t0
t1
bits
128/fS 128/fS
Data CRC CRC EOF
10 10 10 12
bits bits bits bits
t2
Input Data Transfer using ASK
Output Data Transfer using 847kHz BPSK
SOF
AI09060
3.10
CRC
The 16-bit CRC that is used by the SR176 follows the ISO 14443 Type B recommendation.
For further information, see Appendix A. The initial register content is all ones: FFFFh.
A two-byte CRC is appended to each Request and each Answer, within each frame, before
the EOF. The CRC is calculated on all the Bytes after the SOF, up to the CRC field.
On reception of a Request from a reader, the SR176 verifies that the CRC value is valid. If it
is invalid, it discards the frame and does not answer the reader.
On reception of an Answer from the SR176, it is recommended that the reader verify that the
CRC value is valid. If it is invalid, that choice of actions that are to be performed are the
responsibility of the reader designer.
The CRC is transmitted least significant byte first. Each byte is transmitted least significant
bit first.
Figure 11. CRC transmission rules
LSbit
LSByte
MSbit LSbit
MSByte
MSbit
CRC 16 (8 bits)
CRC 16 (8 bits)
ai07667
11/35