DOC7707 datasheet(177/307 Pages) ETC1

177 / 307 page

177

7707F–AVR–11/10

AT90USB82/162

Note:

1. See “About Code Examples” on page 7.

18.5

Data Transfer

Using the USART in MSPI mode requires the Transmitter to be enabled, i.e. the TXENn bit in

the UCSRnB register is set to one. When the Transmitter is enabled, the normal port operation

of the TxDn pin is overridden and given the function as the Transmitter's serial output. Enabling

the receiver is optional and is done by setting the RXENn bit in the UCSRnB register to one.

When the receiver is enabled, the normal pin operation of the RxDn pin is overridden and given

the function as the Receiver's serial input. The XCKn will in both cases be used as the transfer

clock.

After initialization the USART is ready for doing data transfers. A data transfer is initiated by writ-

ing to the UDRn I/O location. This is the case for both sending and receiving data since the

Assembly Code Example

(1)

USART_Init:

clr

r18

out

UBRRnH,r18

out

UBRRnL,r18

; Setting the XCKn port pin as output, enables master mode.

sbi

XCKn_DDR, XCKn

; Set MSPI mode of operation and SPI data mode 0.

ldi

r18, (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn)

out

UCSRnC,r18

; Enable receiver and transmitter.

ldi

r18, (1<<RXENn)|(1<<TXENn)

out

UCSRnB,r18

; Set baud rate.

; IMPORTANT: The Baud Rate must be set after the transmitter is enabled!

out

UBRRnH, r17

out

UBRRnL, r18

ret

C Code Example

(1)

void

USART_Init( unsigned int baud )

{

UBRRn = 0;

/* Setting the XCKn port pin as output, enables master mode. */

XCKn_DDR |= (1<<XCKn);

/* Set MSPI mode of operation and SPI data mode 0. */

UCSRnC = (1<<UMSELn1)|(1<<UMSELn0)|(0<<UCPHAn)|(0<<UCPOLn);

/* Enable receiver and transmitter. */

UCSRnB = (1<<RXENn)|(1<<TXENn);

/* Set baud rate. */

/* IMPORTANT: The Baud Rate must be set after the transmitter is enabled

UBRRn = baud;

}

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