ATmega16 datasheet(159/357 Pages) ATMEL

159 / 357 page

159

2466S–AVR–05/09

ATmega16(L)

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

Table 61) 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.

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 61 and Table 62 list the maximum receiver baud rate error that can be tolerated. Note that

Normal Speed mode has higher toleration of baud rate variations.

Table 61. Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode (U2X =

# (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

Table 62. Recommended Maximum Receiver Baud Rate Error for Double Speed Mode (U2X =

# (Data+Parity Bit)

Rslow (%)

Rfast (%)

Max Total

Error (%)

Recommended Max

Receiver Error (%)

94.12

105.66

+5.66/-5.88

± 2.5

94.92

104.92

+4.92/-5.08

± 2.0

95.52

104.35

+4.35/-4.48

± 1.5

Rslow

D 1

()S

S 1

–

⋅

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

Rfast

D 2

()S

D 1

()SS

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

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