AT90PWM2 datasheet(199/361 Pages) ATMEL

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199

4317J–AVR–08/10

AT90PWM2/3/2B/3B

18.8.3

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

Table 18-2) 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 SF = 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.

fast is the ratio of the fastest incoming data rate that can be accepted in relation to the

receiver baud rate.

Table 18-2 and Table 18-3 list the maximum receiver baud rate error that can be tolerated. Note

that Normal Speed mode has higher toleration of baud rate variations.

Table 18-2.

Recommended Maximum Receiver Baud Rate Error for Normal Speed Mode

(U2X = 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

()SS

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

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