ATmega328P datasheet(184/345 Pages) ATMEL

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184

7810A–AVR–11/09

ATmega328P [Preliminary]

The following equations can be used to calculate the ratio of the incoming data rate and internal

receiver baud rate.

Sum of character size and parity size (D = 5 to 10 bit)

Samples per bit. S = 16 for Normal Speed mode and S = 8 for Double Speed

mode.

First sample number used for majority voting. S

F = 8 for normal speed and

F = 4 for Double Speed mode.

Middle sample number used for majority voting. S

M = 9 for normal speed and

M = 5 for Double Speed mode.

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)

# (Data+Parity Bit)

slow (%)

fast (%)

Max Total Error (%)

Recommended Max

Receiver Error (%)

93.20

106.67

+6.67/-6.8

± 3.0

94.12

105.79

+5.79/-5.88

± 2.5

94.81

105.11

+5.11/-5.19

± 2.0

95.36

104.58

+4.58/-4.54

± 2.0

95.81

104.14

+4.14/-4.19

± 1.5

96.17

103.78

+3.78/-3.83

± 1.5

Rslow

D 1

()S

S 1

–

⋅

---------------------------------------------

Rfast

D 2

()S

D 1

()SSM

-----------------------------------

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