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16
APPENDIX − MANCHESTER ENCODING
All Fieldbus devices transmit the data onto the media as
a Manchester-encoded baseband signal. With Manchester
encoding, zeros and ones are represented by transitions that
occur in the middle of the bit period (see below). For
FOUNDATION Fieldbus H1 and Profibus PA, the nominal
bit time is 32 msec, with the transition occurring at 16 msec.
The Manchester encoding rules have been extended to
include two additional symbols, non-data plus (N+) and
non-data minus (N−). The symbol encoding rules are shown
in Figure 13.
Figure 13. Manchester Encoding
Logical ”0”
T
2
−T
2
”N+”
T
2
−T
2
”N−”
T
2
−T
2
Logical ”1”
T
2
−T
2
32 usec
