
183
2570N–AVR–05/11
ATmega325/3250/645/6450
Bit 3 – USBSn: Stop Bit Select
This bit selects the number of stop bits to be inserted by the Transmitter. The Receiver ignores
this setting.
Bit 2:1 – UCSZn1:0: Character Size
The UCSZn1:0 bits combined with the UCSZn2 bit in UCSRnB sets the number of data bits
(Character SiZe) in a frame the Receiver and Transmitter use.
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 (XCK).
Table 20-10. USBS Bit Settings
USBSn
Stop Bit(s)
01-bit
12-bit
Table 20-11. UCSZ Bits Settings
UCSZn2
UCSZn1
UCSZn0
Character Size
0
5-bit
0
1
6-bit
0
1
0
7-bit
011
8-bit
100
Reserved
101
Reserved
110
Reserved
1
9-bit
Table 20-12. UCPOL Bit Settings
UCPOLn
Transmitted Data Changed
(Output of TxD Pin)
Received Data Sampled
(Input on RxD Pin)
0
Rising XCK Edge
Falling XCK Edge
1
Falling XCK Edge
Rising XCK Edge