
191
7810C–AVR–10/12
Atmel ATmega328P [Preliminary]
Bit 0 – UCPOLn: Clock Polarity
This bit is used for synchronous mode only. Write this bit to zero when asynchronous mode is
used. The UCPOLn bit sets the relationship between data output change and data input sample,
and the synchronous clock (XCKn).
19.10.5
UBRRnL and UBRRnH – USART Baud Rate Registers
Bit 15:12 – Reserved Bits
These bits are reserved for future use. For compatibility with future devices, these bit must be
written to zero when UBRRnH is written.
Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRnH contains the four
most significant bits, and the UBRRnL contains the eight least significant bits of the USART
baud rate. Ongoing transmissions by the Transmitter and Receiver will be corrupted if the baud
rate is changed. Writing UBRRnL will trigger an immediate update of the baud rate prescaler.
Table 19-7.
UCSZn Bits Settings
UCSZn2
UCSZn1
UCSZn0
Character Size
00
0
5-bit
00
1
6-bit
01
0
7-bit
01
1
8-bit
1
0
Reserved
1
0
1
Reserved
1
0
Reserved
11
1
9-bit
Table 19-8.
UCPOLn Bit Settings
UCPOLn
Transmitted Data Changed (Output of
TxDn Pin)
Received Data Sampled (Input on RxDn
Pin)
0
Rising XCKn Edge
Falling XCKn Edge
1
Falling XCKn Edge
Rising XCKn Edge
Bit
151413
1211
10
9
8
–
UBRRn[11:8]
UBRRnH
UBRRn[7:0]
UBRRnL
76
54
32
10
Read/Write
R
R/W
Initial Value
0
00