Datasheet

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.
Table 19-2 on page 184 and Table 19-3 on page 185 list the maximum receiver baud rate error
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
R
slow
D 1+()S
S 1– DS⋅ S
F
++
-------------------------------------------=
R
fast
D 2+()S
D 1+()SS
M
+
-----------------------------------=