ATMEGA325-16AJ ATMEL [ATMEL Corporation], ATMEGA325-16AJ Datasheet - Page 170

• Manufacturer Part Number: ATMEGA325-16AJ
• Description: 8-bit Microcontroller with In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

USART Control and Status
Register n B – UCSRnB
170
ATmega325/3250/645/6450
• 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: 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 (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 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 effec-
tively doubling 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 writ-
ten 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 MPCMn set-
ting. For more detailed information see “Multi-processor Communication Mode” on page
168.
• Bit 7 – RXCIEn: RX Complete Interrupt Enable
Writing this bit to one enables interrupt on the RXCn Flag. A USART Receive Complete
interrupt will be generated only if the RXCIEn bit is written to one, the Global Interrupt
Flag in SREG is written to one and the RXCn bit in UCSRnA is set.
• Bit 6 – TXCIEn: TX Complete Interrupt Enable
Writing this bit to one enables interrupt on the TXCn Flag. A USART Transmit Complete
interrupt will be generated only if the TXCIEn bit is written to one, the Global Interrupt
Flag in SREG is written to one and the TXCn bit in UCSRnA is set.
• Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable
Writing this bit to one enables interrupt on the UDREn Flag. A Data Register Empty
interrupt will be generated only if the UDRIEn bit is written to one, the Global Interrupt
Flag in SREG is written to one and the UDREn bit in UCSRnA is set.
• Bit 4 – RXENn: 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 FEn, DORn, and UPEn Flags.
Bit
Read/Write
Initial Value
RXCIEn
R/W
7
0
TXCIEn
R/W
6
0
UDRIEn
R/W
5
0
RXENn
R/W
4
0
TXENn
R/W
3
0
UCSZn2
R/W
2
0
RXB8n
R
1
0
TXB8n
R/W
0
0
2570A–AVR–09/04
UCSRnB