ATMEga64L ATMEL Corporation, ATMEga64L Datasheet - Page 191

• Manufacturer Part Number: ATMEga64L
• Description: 8-bit AVR Microcontroller with 64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

USART Baud Rate Registers –
UBRRL and UBRRH
Examples of Baud Rate
Setting
2490G–AVR–03/04
(1)
Note:
• 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 – UBRR11:0: USART Baud Rate Register
This is a 12-bit register which contains the USART baud rate. The UBRRH contains the
four most significant bits, and the UBRRL contains the eight least significant bits of the
USART baud rate. Ongoing transmissions by the Transmitter and Receiver will be cor-
rupted if the baud rate is changed. Writing UBRRL will trigger an immediate update of
the baud rate prescaler.
For standard crystal and resonator frequencies, the most commonly used baud rates for
asynchronous operation can be generated by using the UBRR settings in Table 82 to
Table 85. UBRR values which yield an actual baud rate differing less than 0.5% from the
target baud rate, are bold in the table. Higher error ratings are acceptable, but the
receiver will have less noise resistance when the error ratings are high, especially for
large serial frames (see “Asynchronous Operational Range” on page 184). The error
values are calculated using the following equation:
Bit
Read/Write
Initial Value
1. UBRRH is not available in mega103 compatibility mode
R/W
15
R
–
7
0
0
Error[%]
R/W
14
R
–
6
0
0
=
R/W
13
R
–
5
0
0


BaudRate
------------------------------------------------------- - 1
BaudRate
R/W
12
R
–
4
0
0
UBRR[7:0]
Closest Match
R/W
R/W
11
3
0
0
–
R/W
R/W


10
2
0
0
UBRR[11:8]
•
100%
ATmega64(L)
R/W
R/W
9
1
0
0
R/W
R/W
8
0
0
0
UBRRH
UBRRL
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