Atmel Evaluation Kit AT91SAM9M10-G45-EK AT91SAM9M10-G45-EK Data Sheet

 484

SAM9M10 [DATASHEET]

6355F–ATARM–12-Mar-13

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 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 

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 during one quarter of a bit time at zero, a start bit is detected. See 

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 quar-
ters 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 at 1. See 

 for an example of

Manchester error detection during data phase. 

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