
184
7810C–AVR–10/12
Atmel ATmega328P [Preliminary]
The following equations can be used to calculate the ratio of the incoming data rate and internal
receiver baud 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.
that can be tolerated. Note that Normal Speed mode has higher toleration of baud rate
variations.
Table 19-2.
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
Rslow
D 1
+
()S
S 1
–
DS
SF
++
-------------------------------------------
=
Rfast
D 2
+
()S
D 1
+
()SS
M
+
-----------------------------------
=