196
AT90PWM216/316 [DATASHEET]
7710H–AVR–07/2013
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 corrupted if the baud rate is changed. Writing UBRRL will trigger an immediate
update of the baud rate prescaler.
17.11 Examples of Baud Rate Setting
For standard crystal, resonator and external oscillator frequencies, the most commonly used baud rates for asyn-
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
using the following equation:
Error[%]
1
BaudRate
Closest Match
BaudRate
--------------------------------------------------------
–
100%
=
Table 17-9.
Examples of UBRR Settings for Commonly Frequencies
Baud
Rate
(bps)
fclk
io = 1.0000 MHz
fclk
io = 1.8432 MHz
fclk
io = 2.0000 MHz
U2X = 0
U2X = 1
U2X = 0
U2X = 1
U2X = 0
U2X = 1
UBRR
Error
UBRR
Error
UBRR
Error
UBRR
Error
UBRR
Error
UBRR
Error
2400
25
0.2%
51
0.2%
47
0.0%
95
0.0%
51
0.2%
103
0.2%
4800
12
0.2%
25
0.2%
23
0.0%
47
0.0%
25
0.2%
51
0.2%
9600
6
-7.0%
12
0.2%
11
0.0%
23
0.0%
12
0.2%
25
0.2%
14.4k
3
8.5%
8
-3.5%
7
0.0%
15
0.0%
8
-3.5%
16
2.1%
19.2k
2
8.5%
6
-7.0%
5
0.0%
11
0.0%
6
-7.0%
12
0.2%
28.8k
1
8.5%
3
8.5%
3
0.0%
7
0.0%
3
8.5%
8
-3.5%
38.4k
1
-18.6%
2
8.5%
2
0.0%
5
0.0%
2
8.5%
6
-7.0%
57.6k
0
8.5%
1
8.5%
1
0.0%
3
0.0%
1
8.5%
3
8.5%
76.8k
–
1
-18.6%
1
-25.0%
2
0.0%
1
-18.6%
2
8.5%
115.2k
–
0
8.5%
0
0.0%
1
0.0%
0
8.5%
1
8.5%
230.4k
–––
0
0.0%
–
––
–
250k
–––
––
–
500k
–––
––
–
1M
–––
––
–
Max. (1)
62.5 kbps
125 kbps
115.2 kbps
230.4 Kbps
125 kpbs
250 kbps
1.
UBRR = 0, Error = 0.0%