ATmega328P datasheet(197/448 Pages) ATMEL

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8161D–AVR–10/09

ATmega48PA/88PA/168PA/328P

• Bit 5 – UDRIEn: USART Data Register Empty Interrupt Enable n

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 n

Writing this bit to one enables the USART Receiver. The Receiver will override normal port oper-

ation for the RxDn pin when enabled. Disabling the Receiver will flush the receive buffer

invalidating the FEn, DORn, and UPEn Flags.

• Bit 3 – TXENn: Transmitter Enable n

Writing this bit to one enables the USART Transmitter. The Transmitter will override normal port

operation for the TxDn pin when enabled. The disabling of the Transmitter (writing TXENn 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 trans-

mitted. When disabled, the Transmitter will no longer override the TxDn port.

• Bit 2 – UCSZn2: Character Size n

The UCSZn2 bits combined with the UCSZn1:0 bit in UCSRnC sets the number of data bits

(Character SiZe) in a frame the Receiver and Transmitter use.

• Bit 1 – RXB8n: Receive Data Bit 8 n

RXB8n 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 UDRn.

• Bit 0 – TXB8n: Transmit Data Bit 8 n

TXB8n 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 UDRn.

19.10.4

UCSRnC – USART Control and Status Register n C

• Bits 7:6 – UMSELn1:0 USART Mode Select

These bits select the mode of operation of the USARTn as shown in Table 19-4.

Note:

1. See ”USART in SPI Mode” on page 204 for full description of the Master SPI Mode (MSPIM)

operation

Bit

UMSELn1

UMSELn0

UPMn1

UPMn0

USBSn

UCSZn1

UCSZn0

UCPOLn

UCSRnC

Read/Write

R/W

Initial Value

Table 19-4.

UMSELn Bits Settings

UMSELn1

UMSELn0

Mode

Asynchronous USART

Synchronous USART

(Reserved)

Master SPI (MSPIM)(1)

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