Rainbow-electronics ATmega128RFA1 Manual de usuario Pagina 365

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8266A-MCU Wireless-12/09
ATmega128RFA1
Bit 3:0 – UBRR11:8 - USART Baud Rate Register
These bits represent bits [11:8] of the Baud Rate Register. Sample values for
commonly used clock frequencies can be found in section "Examples of Baud Rate
Setting".
23.10.12 UBRR1L – USART1 Baud Rate Register Low Byte
Bit 7 6 5 4 3 2 1 0
NA ($CC) UBRR7 UBRR6 UBRR5 UBRR4 UBRR3 UBRR2 UBRR1 UBRR0 UBRR1L
Read/Write RW RW RW RW RW RW RW RW
Initial Value 0 0 0 0 0 0 0 0
UBRR1 is a 12-bit register which contains the USART baud rate. The UBRR1H
contains the four most significant bits, and the UBRR1L 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 UBRR1L will trigger an
immediate update of the baud rate prescaler.
Bit 7:0 – UBRR7:0 - USART Baud Rate Register
These bits represent bits [7:0] of the Baud Rate Register. Sample values for commonly
used clock frequencies can be found in section "Examples of Baud Rate Setting".
23.11 Examples of Baud Rate Setting
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 23-14
below to Table 23-16 on page 367. 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 353). The error values are calculated using the following equation:
[ ]
%1001%
=
BaudRate
BaudRate
Error
MatchClosest
Table 23-14. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies
fOSC = 1.8432 MHz fOSC = 2.0000 MHz fOSC = 3.6864 MHz
U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1
Baud
Rate
(bps)
UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error
2400 47 0.0% 95 0.0% 51 0.2% 103 0.2% 95 0.0% 191 0.0%
4800 23 0.0% 47 0.0% 25 0.2% 51 0.2% 47 0.0% 95 0.0%
9600 11 0.0% 23 0.0% 12 0.2% 25 0.2% 23 0.0% 47 0.0%
14.4k 7 0.0% 15 0.0% 8 -3.5% 16 2.1% 15 0.0% 31 0.0%
19.2k 5 0.0% 11 0.0% 6 -7.0% 12 0.2% 11 0.0% 23 0.0%
28.8k 3 0.0% 7 0.0% 3 8.5% 8 -3.5% 7 0.0% 15 0.0%
38.4k 2 0.0% 5 0.0% 2 8.5% 6 -7.0% 5 0.0% 11 0.0%
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