Rainbow-electronics ATmega32L Manuel d'utilisateur télécharger pdf (Page 154)

154

ATmega32(L)

2503C–AVR–10/02

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.

The recommendations of the maximum receiver baud rate error was made under the

assumption that the receiver and transmitter equally divides the maximum total error.

There are two possible sources for the receivers baud rate error. The receiver’s system

clock (XTAL) will always have some minor instability over the supply voltage range and

the temperature range. When using a crystal to generate the system clock, this is rarely

a problem, but for a resonator the system clock may differ more than 2% depending of

the resonators tolerance. The second source for the error is more controllable. The baud

rate generator can not always do an exact division of the system frequency to get the

baud rate wanted. In this case an UBRR value that gives an acceptable low error can be

used if possible.

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

(U2X = 0)

# (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

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

(U2X = 1)

# (Data+Parity Bit) R

slow

(%) R

fast

(%)

Max Total

Error (%)

Recommended Max

Receiver Error (%)

5 94.12 105.66 +5.66/-5.88 ± 2.5

6 94.92 104.92 +4.92/-5.08 ± 2.0

7 95.52 104.35 +4.35/-4.48 ± 1.5

8 96.00 103.90 +3.90/-4.00 ± 1.5

9 96.39 103.53 +3.53/-3.61 ± 1.5

10 96.70 103.23 +3.23/-3.30 ± 1.0

1 2 ... 149 150 151 152 153 154 155 156 157 158 159 ... 312 313

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Rainbow-electronics ATmega32L Manuel d'utilisateur Page 154

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