Atmel Evaluation Kit AT91SAM9X35-EK AT91SAM9X35-EK Data Sheet
Product codes
AT91SAM9X35-EK
772
SAM9X35 [DATASHEET]
11055E–ATARM–10-Mar-2014
Figure 39-6. 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 Register of the transmitter and
US_THR becomes empty, thus TXRDY rises.
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 Register 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.
is low has no effect and the written character is lost.
Figure 39-7. Transmitter Status
39.7.3.2 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, a transition
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 signal (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.
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.
Figure 39-8. NRZ to Manchester Encoding
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