SAM3SD8C Atmel Corporation, SAM3SD8C Datasheet - Page 717

• Manufacturer Part Number: SAM3SD8C
• Manufacturer: Atmel Corporation

32.7.3.4
11090A–ATARM–10-Feb-12
11090A–ATARM–10-Feb-12
Manchester Decoder
Figure 32-13. Asynchronous Character Reception
When the MAN field in US_MR register 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 indepen-
dent 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 addi-
tion, 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
Unlike preamble, the start frame delimiter is shared between Manchester Encoder and Decoder.
So, if ONEBIT field is set to 1, only a zero encoded Manchester can be detected as a valid start
frame delimiter. If ONEBIT is set to 0, only a sync pattern is detected as a valid start frame
delimiter. Decoder operates by detecting transition on incoming stream. If RXD is sampled dur-
ing one quarter of a bit time to zero, a start bit is detected. See
rejection mechanism applies.
Figure 32-14. Asynchronous Start Bit Detection
The receiver is activated and starts Preamble and Frame Delimiter detection, sampling the data
at one quarter and then three quarters. If a valid preamble pattern or start frame delimiter is
detected, the receiver continues decoding with the same synchronization. If the stream does not
match a valid pattern or a valid start frame delimiter, the receiver re-synchronizes on the next
valid edge.The minimum time threshold to estimate the bit value is three quarters of a bit time.
If a valid preamble (if used) followed with a valid start frame delimiter is detected, the incoming
stream is decoded into NRZ data and passed to USART for processing.
Manchester pattern mismatch. When incoming data stream is passed to the USART, the
receiver is also able to detect Manchester code violation. A code violation is a lack of transition
Manchester
Sampling
Baud Rate
Example: 8-bit, Parity Enabled
Detection
encoded
(16 x)
Clock
Start
Clock
RXD
data
Txd
samples
16
1
D0
2
samples
Figure 32-9
16
3
D1
4
samples
16
Detection
D2
Start
samples
for available preamble patterns.
16
D3
samples
16
D4
samples
16
D5
samples
16
Figure
D6
samples
16
SAM3S8/SD8
SAM3S8/SD8
32-14. The sample pulse
Figure 32-15
D7
samples
16
Parity
Bit
samples
16
Stop
illustrates
Bit
717
717