AT32UC3C1512C Automotive Atmel Corporation, AT32UC3C1512C Automotive Datasheet - Page 576

• Manufacturer Part Number: AT32UC3C1512C Automotive
• Manufacturer: Atmel Corporation

25.6.3.4
9166C–AVR-08/11
Manchester Decoder
When the MAN field in 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 Man-
chester 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 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 MAN register.
Depending on the desired application the preamble pattern matching is to be defined via the
RX_PP field in 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 at zero, a start bit is detected. See
rejection mechanism applies.
Figure 25-13. 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
in the middle of a bit cell. In this case, MANE flag in CSR register is raised. It is cleared by writing
the Control Register (CR) with the RSTSTA bit at 1. See
chester error detection during data phase.
Manchester
Sampling
encoded
(16 x)
Clock
data
Txd
Figure 25-8
1
2
3
4
for available preamble patterns.
Detection
Start
Figure 25-15
Figure
25-13. The sample pulse
for an example of Man-
Figure 25-14
AT32UC3C
illustrates
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