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参数资料
| 型号： | IT80C52CXXX-L16R |
| 厂商： | ATMEL CORP |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 8-BIT, MROM, 16 MHz, MICROCONTROLLER, PQFP44 |
| 封装： | 1 MM HEIGHT, TQFP-44 |
| 文件页数： | 43/298页 |
| 文件大小： | 8529K |
| 代理商： | IT80C52CXXX-L16R |
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137
ATmega8A [DATASHEET]
8159E–AVR–02/2013
20.6.9
Receive Compete Flag and Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXC) Flag indicates if there are unread data present in the receive buffer. This flag is one
when unread data exist in the receive buffer, and zero when the receive buffer is empty (i.e., does not contain any
unread data). If the Receiver is disabled (RXEN = 0), the receive buffer will be flushed and consequently the RXC
bit will become zero.
When the Receive Complete Interrupt Enable (RXCIE) in UCSRB is set, the USART Receive Complete Interrupt
will be executed as long as the RXC Flag is set (provided that global interrupts are enabled). When interrupt-driven
data reception is used, the receive complete routine must read the received data from UDR in order to clear the
RXC Flag, otherwise a new interrupt will occur once the interrupt routine terminates.
20.6.10
Receiver Error Flags
The USART Receiver has three error flags: Frame Error (FE), Data OverRun (DOR) and Parity Error (PE). All can
be accessed by reading UCSRA. Common for the error flags is that they are located in the receive buffer together
with the frame for which they indicate the error status. Due to the buffering of the error flags, the UCSRA must be
read before the receive buffer (UDR), since reading the UDR I/O location changes the buffer read location. Another
equality for the error flags is that they can not be altered by software doing a write to the flag location. However, all
flags must be set to zero when the UCSRA is written for upward compatibility of future USART implementations.
None of the error flags can generate interrupts.
The Frame Error (FE) Flag indicates the state of the first stop bit of the next readable frame stored in the receive
buffer. The FE Flag is zero when the stop bit was correctly read (as one), and the FE Flag will be one when the
stop bit was incorrect (zero). This flag can be used for detecting out-of-sync conditions, detecting break conditions
and protocol handling. The FE Flag is not affected by the setting of the USBS bit in UCSRC since the Receiver
ignores all, except for the first, stop bits. For compatibility with future devices, always set this bit to zero when writ-
ing to UCSRA.
The Data OverRun (DOR) Flag indicates data loss due to a Receiver buffer full condition. A Data OverRun occurs
when the receive buffer is full (two characters), it is a new character waiting in the Receive Shift Register, and a
new start bit is detected. If the DOR Flag is set there was one or more serial frame lost between the frame last read
from UDR, and the next frame read from UDR. For compatibility with future devices, always write this bit to zero
when writing to UCSRA. The DOR Flag is cleared when the frame received was successfully moved from the Shift
Register to the receive buffer.
The Parity Error (PE) Flag indicates that the next frame in the receive buffer had a parity error when received. If
parity check is not enabled the PE bit will always be read zero. For compatibility with future devices, always set this
bit to zero when writing to UCSRA. For more details see “Parity Bit Calculation” on page 130 and “Parity Checker”
20.6.11
Parity Checker
The Parity Checker is active when the high USART Parity mode (UPM1) bit is set. Type of parity check to be per-
formed (odd or even) is selected by the UPM0 bit. When enabled, the Parity Checker calculates the parity of the
data bits in incoming frames and compares the result with the parity bit from the serial frame. The result of the
check is stored in the receive buffer together with the received data and stop bits. The Parity Error (PE) Flag can
then be read by software to check if the frame had a parity error.
The PE bit is set if the next character that can be read from the receive buffer had a parity error when received and
the parity checking was enabled at that point (UPM1 = 1). This bit is valid until the receive buffer (UDR) is read.
20.6.12
Disabling the Receiver
In contrast to the Transmitter, disabling of the Receiver will be immediate. Data from ongoing receptions will there-
fore be lost. When disabled (i.e., the RXEN is set to zero) the Receiver will no longer override the normal function
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相关代理商/技术参数 |
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