at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 469

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

6384B–ATARM–15-Dec-08
sists of a user-defined pattern that indicates the beginning of a valid data.
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 seri-
ally 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
Figure 32-8. NRZ to Manchester Encoding
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 US_MAN register, the
field TX_PL is used to configure the preamble length.
valid patterns. To improve flexibility, the encoding scheme can be configured using the
TX_MPOL field in the US_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 tran-
sition. 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 32-9. Preamble Patterns, Default Polarity Assumed
A start frame delimiter is to be configured using the ONEBIT field in the US_MR register. It con-
Manchester
Manchester
Manchester
Manchester
encoded
encoded
encoded
encoded
data
data
data
data
Manchester
encoded
encoded
NRZ
data
data
Txd
Txd
Txd
Txd
Txd
8 bit width "ZERO_ONE" Preamble
8 bit width "ONE_ZERO" Preamble
8 bit width "ALL_ZERO" Preamble
1
8 bit width "ALL_ONE" Preamble
0
1
AT91SAM9G20 Preliminary
1
0
Figure 32-9
0
0
illustrates and defines the
SFD
SFD
SFD
SFD
1
Figure 32-10
DATA
DATA
DATA
DATA
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