Atmel Evaluation Kit AT91SAM9M10-G45-EK AT91SAM9M10-G45-EK Hoja De Datos
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AT91SAM9M10-G45-EK
480
SAM9M10 [DATASHEET]
6355F–ATARM–12-Mar-13
Figure 31-6.
Character Transmit
The characters are sent by writing in the Transmit Holding Register (US_THR). The transmitter reports two status
bits in the Channel Status Register (US_CSR): TXRDY (Transmitter Ready), which indicates that US_THR is
empty and TXEMPTY, which indicates that all the characters written in US_THR have been processed. When the
current character processing is completed, the last character written in US_THR is transferred into the Shift Regis-
ter of the transmitter and US_THR becomes empty, thus TXRDY rises.
bits in the Channel Status Register (US_CSR): TXRDY (Transmitter Ready), which indicates that US_THR is
empty and TXEMPTY, which indicates that all the characters written in US_THR have been processed. When the
current character processing is completed, the last character written in US_THR is transferred into the Shift Regis-
ter of the transmitter and US_THR becomes empty, thus TXRDY rises.
Both TXRDY and TXEMPTY bits are low when the transmitter is disabled. Writing a character in US_THR while
TXRDY is low has no effect and the written character is lost.
TXRDY is low has no effect and the written character is lost.
Figure 31-7.
Transmitter Status
31.7.3.2
Manchester Encoder
When the Manchester encoder is in use, characters transmitted through the USART are encoded based on
biphase Manchester II format. To enable this mode, set the MAN field in the US_MR register to 1. Depending on
polarity configuration, a logic level (zero or one), is transmitted as a coded signal one-to-zero or zero-to-one. Thus,
polarity configuration, a logic level (zero or one), is transmitted as a coded signal one-to-zero or zero-to-one. Thus,
a transition always occurs at the midpoint of each bit time. It consumes more bandwidth than the original NRZ sig-
nal (2x) but the receiver has more error control since the expected input must show a change at the center of a bit
cell. An example of Manchester encoded sequence is: the byte 0xB1 or 10110001 encodes to 10 01 10 10 01 01
01 10, assuming the default polarity of the encoder.
nal (2x) but the receiver has more error control since the expected input must show a change at the center of a bit
cell. An example of Manchester encoded sequence is: the byte 0xB1 or 10110001 encodes to 10 01 10 10 01 01
01 10, assuming the default polarity of the encoder.
illustrates this coding scheme.
Figure 31-8.
NRZ to Manchester Encoding
The Manchester encoded character can also be encapsulated by adding both a configurable preamble and a start
frame delimiter pattern. Depending on the configuration, the preamble is a training sequence, composed of a pre-
frame delimiter pattern. Depending on the configuration, the preamble is a training sequence, composed of a pre-
D0
D1
D2
D3
D4
D5
D6
D7
TXD
Start
Bit
Parity
Bit
Stop
Bit
Example: 8-bit, Parity Enabled One Stop
Baud Rate
Clock
D0
D1
D2
D3
D4
D5
D6
D7
TXD
Start
Bit
Parity
Bit
Stop
Bit
Baud Rate
Clock
Start
Bit
Write
US_THR
D0
D1
D2
D3
D4
D5
D6
D7
Parity
Bit
Stop
Bit
TXRDY
TXEMPTY
NRZ
encoded
data
Manchester
encoded
data
1
0
1
1
0
0
0
1
Txd