192
2467S–AVR–07/09
ATmega128
• 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 (XCKn).
USART Baud Rate
Registers – UBRRnL
and UBRRnH
UBRRnH is not available in mega103 compatibility mode
Table 79. USBSn Bit Settings
USBSn Stop Bit(s)
01-bit
12-bits
Table 80. UCSZn Bits Settings
UCSZn2 UCSZn1 UCSZn0 Character Size
0005-bit
0016-bit
0107-bit
0118-bit
100Reserved
101Reserved
110Reserved
1119-bit
Table 81. 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 151413121110 9 8
– – – – UBRRn[11:8] UBRRnH
UBRRn[7:0] UBRRnL
76543210
Read/Write R R R R R/W R/W R/W R/W
R/W R/W R/W R/W R/W R/W R/W R/W
Initial Value00000000
00000000
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