參數(shù)資料
型號: AT91M40807-33AI
廠商: ATMEL CORP
元件分類: 微控制器/微處理器
英文描述: Microcontroller
中文描述: 32-BIT, MROM, 33 MHz, RISC MICROCONTROLLER, PQFP100
封裝: 1.40 MM HEIGHT, TQFP-100
文件頁數(shù): 104/153頁
文件大小: 1837K
代理商: AT91M40807-33AI
104
AT91X40 Series
1354D
ATARM
05/02
Break
A break condition is a low signal level which has a duration of at least one character
(including start/stop bits and parity).
Transmit Break
The transmitter generates a break condition on the TXD line when STTBRK is set in
US_CR (Control Register). In this case, the character present in the Transmit Shift Reg-
ister is completed before the line is held low.
To cancel a break condition on the TXD line, the STPBRK command in US_CR must be
set. The USART completes a minimum break duration of one character length. The TXD
line then returns to high level (idle state) for at least 12 bit periods to ensure that the end
of break is correctly detected. Then the transmitter resumes normal operation.
The BREAK is managed like a character:
The STTBRK and the STPBRK commands are performed only if the transmitter is
ready (bit TXRDY = 1 in US_CSR)
The STTBRK command blocks the transmitter holding register (bit TXRDY is
cleared in US_CSR) until the break has started
A break is started when the Shift Register is empty (any previous character is fully
transmitted). TXEMPTY is cleared in US_CSR. The break blocks the transmitter
shift register until it is completed (high level for at least 12-bit periods after the
STPBRK command is requested)
In order to avoid unpredictable states:
STTBRK and STPBRK commands must not be requested at the same time
Once an STTBRK command is requested, further STTBRK commands are ignored
until the BREAK is ended (high level for at least 12-bit periods)
All STPBRK commands requested without a previous STTBRK command are
ignored
A byte written into the Transmit Holding Register while a break is pending but not
started (US_CSR.TXRDY = 0) is ignored
It is
not permitted
to write new data in the Transmit Holding Register while a break is
in progress (STPBRK has not been requested), even though TXRDY = 1 in
US_CSR.
A new STTBRK command
must not
be issued until an existing break has ended
(TXEMPTY = 1 in US_CSR)
The standard break transmission sequence is:
1.
Wait for the transmitter ready
(US_CSR.TXRDY = 1)
2.
Send the STTBRK command
(write 0x0200 to US_CR)
3.
Wait for the transmitter ready
(TXRDY = 1 in US_CSR)
4.
Send the STPBRK command
(write 0x0400 to US_CR)
The next byte can then be sent:
5.
Wait for the transmitter ready
(TXRDY = 1 in US_CSR)
6.
Send the next byte
(write byte to US_THR)
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