R
EM4223
Data coding
Data transmitted by the Reader to the Tag is encoded in
PIE format as described in 0 and 0 above. Four symbols
are encoded; ‘0’, ‘1’, SOF and EOF. The Transponder is
able to decode symbols having values as shown in Fig.
10 below.
Values
falling
outside
of
the
limits
in
Table 17 will cause the received data to be rejected and
the EM4223 to wait for an unmodulated carrier of EOF
duration or greater before being ready to receive a new
command.
Symbol
Mean
duration
1 Tari
Limits
Time interval in "Tari"
1
2
3
4
Symbol
'0'
0
1
SOF
½ Tari < ‘0’ ≤ 3/2 Tari
3/2 Tari < ’1’ < 3 Tari
Calibration sequence
2 Tari
1 Tari followed
by 3 Tari
'1'
'EOF'
'SOF'
EOF
4 Tari
≥ 4 Tari
Table 17 - PIE symbols
Fig. 10 - PIE symbols
Data Frame format
The bits transmitted by the Reader to the Transponder
are embedded in a frame as specified in Fig. 11. Before
sending the frame, the Reader ensures that it has
established an unmodulated carrier for duration of at
least Taq (Quiet time) of 300µs.
The frame consists of
a
Start-Of-Frame (SOF),
immediately followed by the data bits and terminated by
an End-Of-Frame (EOF). After sending the EOF the
Reader maintains a steady carrier for sufficient time to
allow all Transponders present to be powered so that
they may send their Reply.
Taq
3 Tari
1Tari
B
B
B
B
Quiet
SOF
EOF
Command + Data
Fig. 11 - Forward link frame format
16
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