Datasheet

21.12.5. USART Baud Rate n Register Low and High byte
The UBRRnL and UBRRnH register pair represents the 16-bit value, UBRRn (n=0,1).The low byte [7:0]
(suffix L) is accessible at the original offset. The high byte [15:8] (suffix H) can be accessed at offset +
0x01. For more details on reading and writing 16-bit registers, refer to Accessing 16-bit Registers.
Name: UBRR0L and UBRR0H, UBRR1L and UBRR1H
Offset: 0xC4 + n*0x08 [n=0..1]
Reset: 0x00
Property: -
Bit 15 14 13 12 11 10 9 8
UBRR[11:8]
Access
R/W R/W R/W R/W
Reset 0 0 0 0
Bit 7 6 5 4 3 2 1 0
UBRR[7:0]
Access
R/W R/W R/W R/W R/W R/W R/W R/W
Reset 0 0 0 0 0 0 0 0
Bits 11:0 – UBRR[11:0]: USART Baud Rate
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 n 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.
Atmel ATmega644A [DATASHEET]
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