AT32UC3L064_1 ATMEL [ATMEL Corporation], AT32UC3L064_1 Datasheet - Page 383

• Manufacturer Part Number: AT32UC3L064_1
• Description: AVR32 32-bit Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

20.7.3.2
32099A–AVR32–06/09
Asynchronous Receiver
stop bits are successively shifted out on the TXD pin at each falling edge of the programmed
serial clock.
The number of data bits is selected by the CHRL field and the MODE 9 bit in the Mode Register
(MR). Nine bits are selected by setting the MODE 9 bit regardless of the CHRL field. The parity
bit is set according to the PAR field in MR. The even, odd, space, marked or none parity bit can
be configured. The MSBF field in MR configures which data bit is sent first. If written at 1, the
most significant bit is sent first. At 0, the less significant bit is sent first. The number of stop bits is
selected by the NBSTOP field in MR. The 1.5 stop bit is supported in asynchronous mode only.
Figure 20-6. Character Transmit
The characters are sent by writing in the Transmit Holding Register (THR). The transmitter
reports two status bits in the Channel Status Register (CSR): TXRDY (Transmitter Ready),
which indicates that THR is empty and TXEMPTY, which indicates that all the characters written
in THR have been processed. When the current character processing is completed, the last
character written in THR is transferred into the Shift Register of the transmitter and THR
becomes empty, thus TXRDY rises.
Both TXRDY and TXEMPTY bits are low when the transmitter is disabled. Writing a character in
THR while TXRDY is low has no effect and the written character is lost.
Figure 20-7. Transmitter Status
If the USART is programmed in asynchronous operating mode (SYNC = 0), the receiver over-
samples the RXD input line. The oversampling is either 16 or 8 times the Baud Rate clock,
depending on the OVER bit in the Mode Register (MR).
Baud Rate
TXEMPTY
Baud Rate
Example: 8-bit, Parity Enabled One Stop
TXRDY
Clock
Write
TXD
THR
Clock
TXD
Start
Bit
Start
Bit
D0
D1
D0
D2
D3
D1
D4
D5
D2
D6
D7
D3
Parity
Bit
Stop
Bit
D4
Start
Bit
D0
D5
D1
D2
D6
D3
D4
D7
D5
AT32UC3L
D6
Parity
Bit
D7
Parity
Bit
Stop
Bit
Stop
Bit
383