Data Sheet
188
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
Using any of the 5- to 8-bit character frame formats is possible, but impractical since the Receiver must change
between using n and n+1 character frame formats. This makes full-duplex operation difficult since the
Transmitter and Receiver uses the same character size setting. If 5- to 8-bit character frames are used, the
Transmitter must be set to use two stop bit (USBSn = 1) since the first stop bit is used for indicating the frame
type.
Do not use Read-Modify-Write instructions (SBI and CBI) to set or clear the MPCMn bit. The MPCMn bit shares
the same I/O location as the TXCn Flag and this might accidentally be cleared when using SBI or CBI
instructions.
20.10 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 UBRRn settings in Table 20-4. UBRRn 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 186). The error values are calculated using the
following equation:
Note: 1. UBRRn = 0, Error = 0.0%
Error[%]
BaudRate
Closest Match
BaudRate
-------------------------------------------------- 1–
100%=
Table 20-4. 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 = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1 U2Xn = 0 U2Xn = 1
UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn Error UBRRn 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––––––00.0%––––
250k – – – – – – – – – – 0 0.0%
Max.
(1)
62.5kbps 125kbps 115.2kbps 230.4kbps 125kbps 250kbps