Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
186
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
20.8.3 Asynchronous Operational Range
The operational range of the Receiver is dependent on the mismatch between the received bit rate and the
internally generated baud rate. If the Transmitter is sending frames at too fast or too slow bit rates, or the
internally generated baud rate of the Receiver does not have a similar (see
internally generated baud rate. If the Transmitter is sending frames at too fast or too slow bit rates, or the
internally generated baud rate of the Receiver does not have a similar (see
) base
frequency, the Receiver will not be able to synchronize the frames to the start bit.
The following equations can be used to calculate the ratio of the incoming data rate and internal receiver baud
rate.
rate.
D
Sum of character size and parity size (D = 5 to 10 bit)
S
Samples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed
mode.
S
F
First sample number used for majority voting. S
F
= 8 for normal speed and S
F
= 4
for Double Speed mode.
S
M
Middle sample number used for majority voting. S
M
= 9 for normal speed and
S
M
= 5 for Double Speed mode.
R
slow
is the ratio of the slowest incoming data rate that can be accepted in relation to the
receiver baud rate. R
fast
is the ratio of the fastest incoming data rate that can be
accepted in relation to the receiver baud rate.
list the maximum receiver baud rate error that can be
tolerated. Note that Normal Speed mode has higher toleration of baud rate variations.
Table 1.
Table 20-2.
Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode (U2Xn = 0)
D
# (Data+Parity Bit)
R
slow
(%)
R
fast
(%)
Max Total Error (%)
Recommended Max
Receiver Error (%)
5
93.20
106.67
+6.67/-6.8
± 3.0
6
94.12
105.79
+5.79/-5.88
± 2.5
7
94.81
105.11
+5.11/-5.19
± 2.0
8
95.36
104.58
+4.58/-4.54
± 2.0
9
95.81
104.14
+4.14/-4.19
± 1.5
10
96.17
103.78
+3.78/-3.83
± 1.5
Table 20-3.
Recommended Maximum Receiver Baud Rate Error for Double Speed Mode (U2Xn = 1)
D
# (Data+Parity Bit)
R
slow
(%)
R
fast
(%)
Max Total Error (%)
Recommended Max
Receiver Error (%)
5
94.12
105.66
+5.66/-5.88
± 2.5
6
94.92
104.92
+4.92/-5.08
± 2.0
7
95.52
104,35
+4.35/-4.48
± 1.5
R
slow
D
1
+
S
S
1
–
D S
S
F
+
+
-------------------------------------------
=
R
fast
D
2
+
S
D
1
+
S S
M
+
-----------------------------------
=