Atmel AVR AT90CAN128, Руководство пользователя

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196
7679H–CAN–08/08
AT90CAN32/64/128
• Bit 6 – TXCn: USARTn Transmit Complete
This flag bit is set when the entire frame in the Transmit Shift Register has been shifted out and
there are no new data currently present in the transmit buffer (UDRn). The TXCn flag bit is auto-
matically cleared when a transmit complete interrupt is executed, or it can be cleared by writing
a one to its bit location. The TXCn flag can generate a Transmit Complete interrupt (see descrip-
tion of the TXCIEn bit).
• Bit 5 – UDREn: USARTn Data Register Empty
The UDREn flag indicates if the transmit buffer (UDRn) is ready to receive new data. If UDREn is
one, the buffer is empty, and therefore ready to be written. The UDREn flag can generate a Data
Register Empty interrupt (see description of the UDRIEn bit).
UDREn is set after a reset to indicate that the Transmitter is ready.
• Bit 4 – FEn: Frame Error
This bit is set if the next character in the receive buffer had a Frame Error when received. I.e.,
when the first stop bit of the next character in the receive buffer is zero. This bit is valid until the
receive buffer (UDRn) is read. The FEn bit is zero when the stop bit of received data is one.
Always set this bit to zero when writing to UCSRnA.
• Bit 3 – DORn: Data OverRun
This bit is set if a Data OverRun condition is detected. 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. This bit is valid until the receive buffer (UDRn) is read. Always set this
bit to zero when writing to UCSRnA.
• Bit 2 – UPEn: USARTn Parity Error
This bit is set if the next character in the receive buffer had a Parity Error when received and the
Parity Checking was enabled at that point (UPMn1 = 1). This bit is valid until the receive buffer
(UDRn) is read. Always set this bit to zero when writing to UCSRnA.
• Bit 1 – U2Xn: Double the USARTn Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using syn-
chronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively dou-
bling the transfer rate for asynchronous communication.
• Bit 0 – MPCMn: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCMn bit is written to
one, all the incoming frames received by the USARnT Receiver that do not contain address
information will be ignored. The Transmitter is unaffected by the MPCMn setting. For more
detailed information see
“Multi-processor Communication Mode” on page 193 .
17.11.5 USART0 Control and Status Register B – UCSR0B
Bit 7 6 5 4 3 2 1 0
RXCIE0 TXCIE0 UDRIE0 RXEN0 TXEN0 UCSZ02 RXB80 TXB80 UCSR0B
Read/Write R/W R/W R/W R/W R/W R/W R R/W
Initial Value 0 0 0 0 0 0 0 0