Atmel SAM4L Xplained Pro Starter Kit Atmel ATSAM4L-XSTK ATSAM4L-XSTK Data Sheet

42023E–SAM–07/2013

1 to 15 bit periods. If the preamble length is zero, the preamble waveform is not generated. The
preamble length is selected by writing to the Transmitter Preamble Length field (MAN.TX_PL).
The available preamble sequence patterns are: 

• ALL_ONE

• ALL_ZERO 

• ONE_ZERO 

• ZERO_ONE

and are selected by writing to the Transmitter Preamble Pattern field (MAN.TX_PP). 

 illustrates the supported patterns. 

Figure 24-46. Preamble Patterns, Default Polarity Assumed 

The Start Frame Delimiter Selector bit (MR.ONEBIT) configures the Manchester start bit pattern

following the preamble. If MR.ONEBIT is one, a Manchester encoded zero is transmitted to indi-
cate that a new character is about to be sent. If MR.ONEBIT is zero, a synchronization pattern is
sent for the duration of three bit periods to inaugurate the new character. The sync pattern wave-
form by itself is an invalid Manchester encoding, since the transition only occurs at the middle of
the second bit period.

The Manchester Synchronization Mode bit (MR.MODSYNC) selects sync pattern, and this also
defines if the character is data (MODSYNC=0) with a zero to one transition, or a command
(MODSYNC=1) with a one to zero transition. When direct memory access is used, the sync pat-
tern can be updated on-the-fly with a modified character located in memory. To enable this
mode the Variable Synchronization of Command/Data Sync Start Frame Delimiter bit
(MR.VAR_SYNC) must be written to one. In this case, MODSYNC is bypassed and

THR.TXSYNH selects the sync type to be included.  

 illustrates supported patterns.

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