18.9.5
UBRRLn and UBRRHn – USART Baud Rate Registers
Bit
15
14
13
12
11
10
9
8
(0xC5)
(0xC4)
–
–
–
–
UBRRn[11:8]
UBRRHn
UBRRLn
UBRRn[7:0]
7
R
6
R
5
R
4
R
3
R/W
R/W
0
2
R/W
R/W
0
1
R/W
R/W
0
0
R/W
R/W
0
Read/Write
Initial Value
R/W
0
R/W
0
R/W
0
R/W
0
0
0
0
0
0
0
0
0
• 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 UBRRHn is written.
• Bit 11:0 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRHn contains the four
most significant bits, and the UBRRLn 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 UBRRLn will trigger an immediate update of the baud rate prescaler.
194
ATmega169P
8018A–AVR–03/06
ATMEL [ ATMEL ]
