192
AT90PWM216/316 [DATASHEET]
7710H–AVR–07/2013
Bit 5 – UDRE: USART Data Register Empty
The UDRE flag indicates if the transmit buffer (UDR) is ready to receive new data. If UDRE is one, the buffer is
empty, and therefore ready to be written. The UDRE flag can generate a Data Register Empty interrupt (see
description of the UDRIE bit).
UDRE is set after a reset to indicate that the Transmitter is ready.
This bit is available in both USART and EUSART modes.
Bit 4 – FE: 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 (UDR) is read. The FE
bit is zero when the stop bit of received data is one. Always set this bit to zero when writing to UCSRA.
This bit is also valid in EUSART mode only when data bits are level encoded (in Manchester mode the FEM bit
allows to detect a framing error).
Bit 3 – DOR: 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 (UDR) is read. Always set this bit to zero when writing to UCSRA.
This bit is available in both USART and EUSART modes.
Bit 2 – UPE: USART 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 (UPM1 = 1). This bit is valid until the receive buffer (UDR) is read. Always set this bit to
zero when writing to UCSRA.
This bit is also valid in EUSART mode only when data bits are level encoded (there is no parity in Manchester
mode).
Bit 1 – U2X: Double the USART Transmission Speed
This bit only has effect for the asynchronous operation. Write this bit to zero when using synchronous operation.
Writing this bit to one will reduce the divisor of the baud rate divider from 16 to 8 effectively doubling the transfer
rate for asynchronous communication.
This bit is available in both USART and EUSART modes.
Bit 0 – MPCM: Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCM bit is written to one, all the incoming
frames received by the USART Receiver that do not contain address information will be ignored. The Transmitter is
This mode is unavailable when the EUSART mode is set.