SAM4L Datasheet, PDF (607/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
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). Figure 24-
45 illustrates the supported patterns.
Figure 24-45. Preamble Patterns, Default Polarity Assumed
Manchester
encoded
data ^Txd
SFD
DATA
8 bit width "ALL_ONE" Preamble
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
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. Figure 24-46 illustrates supported patterns.
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