145
ATmega8A [DATASHEET]
8159E–AVR–02/2013
20.10.3
UCSRB – USART Control and Status Register B
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 written 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 written 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 operation 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 ongo-
ing 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 (Character 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.
20.10.4
UCSRC – USART Control and Status Register C
Bit
7654
3210
RXCIE
TXCIE
UDRIE
RXEN
TXEN
UCSZ2
RXB8
TXB8
UCSRB
Read/Write
R/W
R
R/W
Initial Value
0000
Bit
7654
3210
URSEL
UMSEL
UPM1
UPM0
USBS
UCSZ1
UCSZ0
UCPOL
UCSRC
Read/Write
R/W
Initial Value
1000
0110