AT32AP7001_1 Datasheet, PDF (399/829 Pages) ATMEL Corporation – AVR32 32-bit Microcontroller

AT32AP7001
Figure 25-8. NRZ to Manchester Encoding
NRZ
encoded
data
1
0
1
1
0
0
0
1
Manchester
encoded _Txd
data
The Manchester encoded character can also be encapsulated by adding both a configurable
preamble and a start frame delimiter pattern. Depending on the configuration, the preamble is a
training sequence, composed of a pre-defined pattern with a programmable length from 1 to 15
bit times. If the preamble length is set to 0, the preamble waveform is not generated prior to any
character. The preamble pattern is chosen among the following sequences: ALL_ONE,
ALL_ZERO, ONE_ZERO or ZERO_ONE, writing the field TX_PP in the MAN register, the field
TX_PL is used to configure the preamble length. Figure 25-9 illustrates and defines the valid
patterns. To improve flexibility, the encoding scheme can be configured using the TX_MPOL
field in the MAN register. If the TX_MPOL field is set to zero (default), a logic zero is encoded
with a zero-to-one transition and a logic one is encoded with a one-to-zero transition. If the
TX_MPOL field is set to one, a logic one is encoded with a one-to-zero transition and a logic
zero is encoded with a zero-to-one transition.
Figure 25-9. Preamble Patterns, Default Polarity Assumed
Manchester
encoded
data ^Txd
8 bit width "ALL_ONE" Preamble
SFD
DATA
Manchester
encoded
data ^Txd
Manchester
encoded
data ^Txd
8 bit width "ALL_ZERO" Preamble
8 bit width "ZERO_ONE" Preamble
SFD
DATA
SFD
DATA
Manchester
encoded
data ^Txd
SFD
DATA
8 bit width "ONE_ZERO" Preamble
A start frame delimiter is to be configured using the ONEBIT field in the MR register. It consists
of a user-defined pattern that indicates the beginning of a valid data. Figure 25-10 illustrates
these patterns. If the start frame delimiter, also known as start bit, is one bit, (ONEBIT at 1), a
logic zero is Manchester encoded and indicates that a new character is being sent serially on the
line. If the start frame delimiter is a synchronization pattern also referred to as sync (ONEBIT at
0), a sequence of 3 bit times is sent serially on the line to indicate the start of a new character.
32015G–AVR32–09/09
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