It
may include edge transitions, level detection, pulse width detection, etc. After this ?¬?le
has been created, it becomes the input into the physical layer synthesis tool shown in
Figure 3.3. The textual ?¬?le contains three major segments: (1) declaration of the waveform
to encode data values, (2) declaration of the preamble waveform, and (3) transmission
characteristics for serial to parallel conversion.
Manchester encoding [24] is a ?¬?xed-bit-window encoding scheme speci?¬?ed in ISO 18000
Part 7 for transactions among active RFID readers and tags. The waveforms of encoded
bit 0 and bit 1 are illustrated in Figure 3.4a.
The waveform for encoding a bit as either 0 or 1 is described in Figure 3.5. Sig
represents the nonreturn to zero (NRZ) value of the signal. The keyword after describes
the delay from the beginning of a bit window. The length of the bit window is speci?¬?ed by
a period T. Changes in the signal are represented by an & with a nonzero after parameter.
Finally, A speci?¬?es how accurately each measurement must be as a percentage of T. In the
example from Figure 3.5, a 0 is represented by a 50% duty cycle clock with a falling edge in
the middle of the bit window. The edge must be within 12.5% of the total period,
which means 6.75% of the period before or after the expected transition. In this case, the
transition occurs at 182.
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