Datasheet

SAM9G45 [DATASHEET]
Atmel-6438O-ATARM-SAM9G45-Datasheet_08-Dec-15
586
The number of data bits, first bit sent and parity mode are selected by the same fields and bits as the transmitter,
i.e., respectively CHRL, MODE9, MSBF and PAR. For the synchronization mechanism only, the number of stop
bits has no effect on the receiver as it considers only one stop bit, regardless of the field NBSTOP, so that
resynchronization between the receiver and the transmitter can occur. Moreover, as soon as the stop bit is
sampled, the receiver starts looking for a new start bit so that resynchronization can also be accomplished when
the transmitter is operating with one stop bit.
Figure 32-12 and Figure 32-13 illustrate start detection and character reception when USART operates in
asynchronous mode.
Figure 32-12. Asynchronous Start Detection
Figure 32-13. Asynchronous Character Reception
32.7.3.5 Manchester Decoder
When the MAN field in US_MR is set to 1, the Manchester decoder is enabled. The decoder performs both
preamble and start frame delimiter detection. One input line is dedicated to Manchester encoded input data.
An optional preamble sequence can be defined, its length is user-defined and totally independent of the emitter
side. Use RX_PL in US_MAN register to configure the length of the preamble sequence. If the length is set to 0, no
preamble is detected and the function is disabled. In addition, the polarity of the input stream is programmable with
RX_MPOL field in US_MAN register. Depending on the desired application the preamble pattern matching is to be
defined via the RX_PP field in US_MAN. See Figure 32-9 for available preamble patterns.
Sampling
Clock (x16)
RXD
Start
Detection
Sampling
Baud Rate
Clock
RXD
Start
Rejection
Sampling
12345678
123456701234
123456789 10111213141516
D0
Sampling
D0
D1
D2
D3
D4
D5 D6 D7
RXD
Parity
Bit
Stop
Bit
Example: 8-bit, Parity Enabled
Baud Rate
Clock
Start
Detection
16
samples
16
samples
16
samples
16
samples
16
samples
16
samples
16
samples
16
samples
16
samples
16
samples