Datasheet

198
8272E–AVR–04/2013
ATmega164A/PA/324A/PA/644A/PA/1284/P
19.12 Examples of Baud Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asyn-
chronous operation can be generated by using the UBRR settings in Table 19-9 to Table 19-12.
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 190). The error values are calculated using the following equation:
Error[%]
BaudRate
Closest Match
BaudRate
-------------------------------------------------------- 1–


100%=
Table 19-9. Examples of UBRRn settings for commonly used oscillator frequencies.
Baud
rate
[bps]
f
osc
= 1.0000MHz f
osc
= 1.8432MHz f
osc
= 2.0000MHz
U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1U2Xn = 0U2Xn = 1
UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error
2400 250.2%510.2%470.0%950.0%510.2%1030.2%
4800 120.2%250.2%230.0%470.0%250.2%510.2%
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––––––00.0%––––
250k––––––––––00.0%
Max.
(1)
62.5kbps 125kbps 115.2kbps 230.4kbps 125kbps 250kbps
1. UBRR = 0, Error = 0.0%.