Rainbow-electronics ATmega64L Manuel d'utilisateur télécharger pdf (Page 160)

160

ATmega16(L)

2466B–09/01

• Bit 11:0 - UBRR11:0: USART Baud Rate Register

This is a 12-bit register which contains the USART baud rate. The UBRRH contains the

4 most significant bits, and the UBRRL contains the 8 least significant bits of the USART

baud rate. Ongoing transmissions by the transmitter and receiver will be corrupted if the

baud rate is changed. Writing UBRRL will trigger an immediate update of the baud rate

prescaler.

Examples of Baud Rate

Setting

For standard crystal and resonator frequencies, the most commonly used baud rates for

asynchronous operation can be generated by using the UBRR settings in Table 68.

UBRR values which yield an actual baud rate differing less than 0.5% from the target

baud rate, are bold in the table. Higher error ratings are acceptable, but the receiver will

have less noise resistance when the error ratings are high, especially for large serial

frames (see “Asynchronous Operational Range” on page 151). The error values are cal-

culated using the following equation:

Error[%]

BaudRate

Closest Match

BaudRate

-------------------------------------------------------- 1–

æö

100%•=

Table 68. Examples of UBRR Settings for Commonly Used Oscillator Frequencies

Baud

Rate

(bps)

osc

= 1.0000 MHz f

osc

= 1.8432 MHz f

osc

= 2.0000 MHz

U2X = 0 U2X = 1 U2X = 0 U2X = 1 U2X = 0 U2X = 1

UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error UBRR Error

2400 25 0.2% 51 0.2% 47 0.0% 95 0.0% 51 0.2% 103 0.2%

4800 12 0.2% 25 0.2% 23 0.0% 47 0.0% 25 0.2% 51 0.2%

9600 6 -7.0% 12 0.2% 11 0.0% 23 0.0% 12 0.2% 25 0.2%

14.4k 3 8.5% 8 -3.5% 7 0.0% 15 0.0% 8 -3.5% 16 2.1%

19.2k 2 8.5% 6 -7.0% 5 0.0% 11 0.0% 6 -7.0% 12 0.2%

28.8k 1 8.5% 3 8.5% 3 0.0% 7 0.0% 3 8.5% 8 -3.5%

38.4k 1 -18.6% 2 8.5% 2 0.0% 5 0.0% 2 8.5% 6 -7.0%

57.6k 0 8.5% 1 8.5% 1 0.0% 3 0.0% 1 8.5% 3 8.5%

76.8k - - 1 -18.6% 1 -25.0% 2 0.0% 1 -18.6% 2 8.5%

115.2k - - 0 8.5% 0 0.0% 1 0.0% 0 8.5% 1 8.5%

230.4k------00.0%----

250k----------00.0%

Max

(1)

62.5kbps 125kbps 115.2kbps 230.4Mbps 125kpbs 250kbps

1. UBRR = 0, Error = 0.0%

1 2 ... 155 156 157 158 159 160 161 162 163 164 165 ... 297 298

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Rainbow-electronics ATmega64L Manuel d'utilisateur Page 160

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