ATmega64A
20.11.5 UBRRnL and UBRRnH – USART Baud Rate Registers(1)
Bit
15
14
13
12
11
10
9
8
–
–
–
–
UBRRn[11:8]
UBRRnH
UBRRn[7:0]
UBRRnL
7
R
6
R
5
R
4
R
3
R/W
R/W
0
2
R/W
R/W
0
1
0
Read/Write
Initial Value
R/W
R/W
0
R/W
R/W
0
R/W
0
R/W
0
R/W
0
R/W
0
0
0
0
0
0
0
0
0
Note:
1. UBRRH is not available in mega103 compatibility mode
• 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 UBRRH is written.
• Bit 11:0 – UBRRn11:0: 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.
200
8160C–AVR–07/09
ATMEL [ ATMEL ]
