744
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
In order to increase the compatibility the RXIDLV bit in the US_MAN register allows to inform the
USART block of the Rx line idle state value (Rx line undriven), it can be either level one (pull-up)
or level zero (pull-down). By default this bit is set to one (Rx line is at level 1 if undriven).
Figure 34-14. 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.
illustrates
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
in the middle of a bit cell. In this case, MANE flag in US_CSR register is raised. It is cleared by
writing the Control Register (US_CR) with the RSTSTA bit to 1. See
for an exam-
ple of Manchester error detection during data phase.
Figure 34-15. Preamble Pattern Mismatch
Manchester
encoded
data
Txd
1
2
3
4
Sampling
Clock
(16 x)
Start
Detection
Manchester
encoded
data
Txd
SFD
DATA
Preamble Length is set to 8
Preamble Mismatch
invalid pattern
Preamble Mismatch
Manchester coding error
Содержание SAM4S Series
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