Rainbow-electronics ATmega128L Manual de usuario descargar pdf (Pagina 186)

186

ATmega128(L)

2467B–09/01

• Bit 2:1 - UCSZ1:0: Character Size

The UCSZ1:0 bits combined with the UCSZ2 bit in UCSRB sets the number of data bits

(character size) in a frame the receiver and transmitter use.

• Bit 0 - UCPOL: Clock Polarity

This bit is used for synchronous mode only. Write this bit to zero when asynchronous

mode is used. The UCPOL bit sets the relationship between data output change and

data input sample, and the synchronous clock (XCK).

USART Baud Rate Registers –

UBRRL and UBRRH

UBRRH is not available in mega103 compatibility mode

• Bit 15:12 - Reserved Bits

These bits are reserved for future use. For compatibility with future devices, these bit

must be written to zero when UBRRH is written.

• 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.

Table 80. UCSZ Bits Settings

UCSZ2 UCSZ1 UCSZ0 Character Size

0005-bit

0016-bit

0107-bit

0118-bit

1 0 0 (reserved)

1 0 1 (reserved)

1 1 0 (reserved)

1119-bit

Table 81. UCPOL Bit Settings

UCPOL

Transmitted Data Changed (Output of

TxD Pin)

Received Data Sampled (Input on

RxD Pin)

0 Falling XCK Edge Rising XCK Edge

1 Rising XCK Edge Falling XCK Edge

Bit 151413121110 9 8

–––– UBRR[11:8] UBRRH

UBRR[7:0] UBRRL

76543210

Read/Write R R R R R/W R/W R/W R/W

R/W R/W R/W R/W R/W R/W R/W R/W

Initial value00000000

00000000

1 2 ... 181 182 183 184 185 186 187 188 189 190 191 ... 330 331

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