Rainbow Electronics ATmega128RFA1 - Manual (Page 357)

357
8266A-MCU Wireless-12/09
ATmega128RFA1
• Bit 5 – UDRE0 - USART Data Register Empty
The UDRE0 Flag indicates if the transmit buffer (UDR0) is ready to receive new data. If
UDRE0 is one, the buffer is empty, and therefore ready to be written. The UDRE0 Flag
can generate a Data Register Empty interrupt (see description of the UDRIE0 bit).
UDRE0 is set after a reset to indicate that the Transmitter is ready.
• Bit 4 – FE0 - 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 (UDR0) is read. The FE0 bit is zero when the
stop bit of received data is one. Always set this bit to zero when writing to UCSR0A.
• Bit 3 – DOR0 - 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
(UDR0) is read. Always set this bit to zero when writing to UCSR0A.
• Bit 2 – UPE0 - 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 (UPM01 = 1). This bit is valid until the
receive buffer (UDR0) is read. Always set this bit to zero when writing to UCSR0A.
• Bit 1 – U2X0 - 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.
• Bit 0 – MPCM0 - Multi-processor Communication Mode
This bit enables the Multi-processor Communication mode. When the MPCM0 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 unaffected by the
MPCM0 setting. For more detailed information see section "Multi-processor
Communication Mode".
23.10.3 UCSR0B – USART0 Control and Status Register B
Bit 7 6 5 4 3 2 1 0
NA ($C1) RXCIE0 TXCIE0 UDRIE0 RXEN0 TXEN0 UCSZ02 RXB80 TXB80 UCSR0B
Read/Write RW RW RW RW RW RW R W
Initial Value 0 0 1 0 0 0 0 0
• Bit 7 – RXCIE0 - RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXC0 Flag. A USART Receive Complete
interrupt will be generated only if the RXCIE0 bit is written to one, the Global Interrupt
Flag in SREG is written to one and the RXC0 bit in UCSR0A is set.
• Bit 6 – TXCIE0 - TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXC0 Flag. A USART Transmit Complete
interrupt will be generated only if the TXCIE0 bit is written to one, the Global Interrupt
Flag in SREG is written to one and the TXC0 bit in UCSR0A is set.
• Bit 5 – UDRIE0 - USART Data Register Empty Interrupt Enable