Datasheet

ATmega323(L)

1457E–11/01

• Bit 3 - TXEN: Transmitter Enable

Setting this bit to one enables the USART transmitter. The transmitter will override nor-

mal port operation for the TxD pin when enabled. The disabling of the transmitter

(setting the TXEN to zero) will not become effective until ongoing and pending transmis-

sions are completed, i.e. when the transmit shift register and transmit buffer register

does 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 9th data bit of the received character when operating with serial frames with

9 data bits. Must be read before reading the low bits from UDR.

• Bit 0 - TXB8: Transmit Data Bit 8

TXB8 is the 9th data bit in the character to be transmitted when operating with serial

frames with 9 data bits. Must be written before writing the low bits to UDR.

USART Control and Status

The UCSRC register shares the same I/O location as the UBRRH register. See the

“Accessing UBRRH/UCSRC Registers” on page 91 section which describes how to

access this register.

• Bit 7 - URSEL: Register Select

This bit selects between accessing the UCSRC or the UBRRH register. It is read as one

when reading UCSRC. The URSEL must be one when writing the UCSRC.

• Bit 6 - UMSEL: USART Mode Select

This bit selects between asynchronous and synchronous mode of operation.

• Bit 5:4 - UPM1:0: Parity Mode

This bit enable and set type of parity generation and check. If enabled, the transmitter

will automatically generate and send the parity of the transmitted data bits within each

frame. The receiver will generate a parity value for the incoming data and compare it to

the UPM0 setting. If a mismatch is detected, the PE flag in UCSRA will be set.

Bit 76543210

$20 ($40)

URSEL UMSEL UPM1 UPM0 USBS UCSZ1 UCSZ0 UCPOL UCSRC

Read/Write R/W R/W R/W R/W R/W R/W R/W R/W

Initial Value10000110

Table 32. USART Mode

UMSEL Mode

0 Asynchronous Operation

1 Synchronous Operation