Atmel Xplained Pro Evaluation Kit ATSAM4E-XPRO ATSAM4E-XPRO Hoja De Datos

899

SAM4E [DATASHEET]

Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14

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 to zero, a start bit is detected. See 

. The sample pulse rejection mechanism applies.

The RXIDLEV bit in the US_MAN informs the USART of the receiver line idle state value (receiver line inactive).
The user must define RXIDLEV to ensure reliable synchronization. By default, RXIDLEV is set to one (receiver line
is at level 1 when there is no activity).

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 resynchronizes 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 the US_CSR is raised. It is
cleared by writing the US_CR with the RSTSTA bit to 1. See 

 for an example of Manchester error

detection during data phase. 

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