ATMEGA8_08 Datasheet, PDF (155/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

ATmega8(L)
USART Control and
Status Register B –
UCSRB
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 – 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 infor-
mation will be ignored. The Transmitter is unaffected by the MPCM setting. For more detailed
information see “Multi-processor Communication Mode” on page 151.
Bit
Read/Write
Initial Value
7
RXCIE
R/W
0
6
TXCIE
R/W
0
5
UDRIE
R/W
0
4
RXEN
R/W
0
3
TXEN
R/W
0
2
UCSZ2
R/W
0
1
RXB8
R
0
0
TXB8
R/W
0
UCSRB
• Bit 7 – RXCIE: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXC Flag. A USART Receive Complete interrupt
will be generated only if the RXCIE bit is written to one, the Global Interrupt Flag in SREG is writ-
ten to one and the RXC bit in UCSRA is set.
• Bit 6 – TXCIE: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXC Flag. A USART Transmit Complete interrupt
will be generated only if the TXCIE bit is written to one, the Global Interrupt Flag in SREG is writ-
ten to one and the TXC bit in UCSRA is set.
• Bit 5 – UDRIE: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDRE Flag. A Data Register Empty interrupt will
be generated only if the UDRIE bit is written to one, the Global Interrupt Flag in SREG is written
to one and the UDRE bit in UCSRA is set.
• Bit 4 – RXEN: Receiver Enable
Writing this bit to one enables the USART Receiver. The Receiver will override normal port oper-
ation for the RxD pin when enabled. Disabling the Receiver will flush the receive buffer
invalidating the FE, DOR and PE Flags.
• Bit 3 – TXEN: Transmitter Enable
Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port
operation for the TxD pin when enabled. The disabling of the Transmitter (writing TXEN to zero)
will not become effective until ongoing and pending transmissions are completed (i.e., when the
Transmit Shift Register and Transmit Buffer Register do not contain data to be transmitted).
When disabled, the Transmitter will no longer override the TxD port.
• Bit 2 – UCSZ2: Character Size
The UCSZ2 bits combined with the UCSZ1:0 bit in UCSRC sets the number of data bits (Char-
acter Size) in a frame the Receiver and Transmitter use.
• Bit 1 – RXB8: Receive Data Bit 8
RXB8 is the ninth data bit of the received character when operating with serial frames with nine
data bits. Must be read before reading the low bits from UDR.
• Bit 0 – TXB8: Transmit Data Bit 8
TXB8 is the ninth data bit in the character to be transmitted when operating with serial frames
with nine data bits. Must be written before writing the low bits to UDR.
2486T–AVR–05/08
155