Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Hoja De Datos

SAM4E [DATASHEET]

Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14

896

A start frame delimiter is to be configured using the ONEBIT field in the US_MR register. It consists of a user-

defined pattern that indicates the beginning of a valid data. 

 illustrates these patterns. If the start

frame delimiter, also known as the start bit, is one bit, (ONEBIT to 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 to 0), a sequence of three bit times is sent serially on the line to indicate
the start of a new character. The sync waveform is in itself an invalid Manchester waveform as the transition
occurs at the middle of the second bit time. Two distinct sync patterns are used: the command sync and the data
sync. The command sync has a logic one level for one and a half bit times, then a transition to logic zero for the
second one and a half bit times. If the MODSYNC field in the US_MR is set to 1, the next character is a command.
If it is set to 0, the next character is a data. When direct memory access is used, the MODSYNC field can be
immediately updated with a modified character located in memory. To enable this mode, VAR_SYNC field in
US_MR register must be set to 1. In this case, the MODSYNC field in the US_MR is bypassed and the sync
configuration is held in the TXSYNH in the US_THR. The USART character format is modified and includes sync

information.

Manchester

encoded

data

Txd

SFD

DATA

8 bit width "ALL_ONE"  Preamble

Manchester

encoded

data

Txd

SFD

DATA

8 bit width "ALL_ZERO"  Preamble

Manchester

encoded

data

Txd

SFD

DATA

8 bit width "ZERO_ONE" Preamble

Manchester

encoded

data

Txd

SFD

DATA

8 bit width "ONE_ZERO" Preamble