157
ATmega8515(L)
2512K–AVR–01/10
Writing 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
(writing TXEN to zero) will not become effective until ongoing and pending transmis-
sions are completed. For example, 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 9 data bits. Must be written before writing the low bits to UDR.
USART Control and Status
Register C – UCSRC
The UCSRC Register shares the same I/O location as the UBRRH Register. See the
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
These bits enable and set type of parity generation and check. If enabled, the Transmit-
ter 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 com-
pare it to the UPM0 setting. If a mismatch is detected, the PE Flag in UCSRA will be set.
Bit
7654
321
0
URSEL
UMSEL
UPM1
UPM0
USBS
UCSZ1
UCSZ0
UCPOL
UCSRC
Read/Write
R/W
Initial Value
1000
011
0
Table 63. UMSEL Bit Settings
UMSEL
Mode
0
Asynchronous Operation
1
Synchronous Operation