5%;
??™1??™: Sig????™1??™ after 0 us & ??™1??™ after 18 us;
T??36 us; A??12.5%;
FIGURE 3.5
Textual description of Manchester encoding.
40 RFID Handbook: Applications, Technology, Security, and Privacy
Figure 3.8. In some cases, the period itself may fall within a range that is described by the
error keyword.
The physical layer encodings for FM0 are shown in Figure 3.7b. Unlike PIE, FM0 is a
?¬?xed period encoding. The data rate of FM0 can be one of several discrete values as
speci?¬?ed by the ISO 18000 Part 6C standard, including 160, 256, 320, and 640 kbps. The
corresponding bit window period are 6.2, 3.9, 3.1, and 1.5 ms with the error tolerance of 7%,
10%, 10%, and 15%, respectively. To encode a 0, there must be a transition at the middle of
a bit window. To encode a 1 there is no transition within a bit window; however, between
two adjacent bits, there must be a transition at the edge of the bit window.
The textual representation of FM0 is shown in Figure 3.9. The description for FM0 is
similar to how differential Manchester is described except that each value has four different
representations corresponding to each of the four data rates. In addition, the encoding for 1
is simpler, as it does not have a transition within the bit window and as such has no & in
the waveform description.
Modi?¬?ed Miller encoding [29] is an encoding scheme that is often employed in near ?¬?eld
communication, or communication of 10 cm or less [30].
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