R
EM4223
Tag bits after last transmitted bit
End of last
tag bit
1
2
3
4
5
6
the last tag data transition occurs
at either the centre or end of the
last bit period depending on FM0
state.
Tag not
Tag
reflecting
transmission
Tag listens
Tag Command Window
1st high to low transition of the
command shall occur in this time.
Interrogator
RF field
carrier steady
state level
carrier
modulated
state level
Fig. 13 - Command Window Timing
6. RETURN LINK DATA ENCODING - TRANSPORTER TO READER
The return link data is modulated onto the impinging illuminating RF carrier using varying impedance modulation.
Return link data encoding
Data is encoded using Bi-phase space (FM0).
FM0 Data Coding
MSB first encoding of Byte 10110001 = 'B1'
1
0
1
1
0
0
0
1
Alternative
depending on
prior conditions
t
Trlb
Fig. 14 - Return link – data encoding
18
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