Datasheet

ATmega164A/PA/324A/PA/644A/PA/1284/P
 2018 Microchip Technology Inc. Data Sheet Complete DS40002070A-page 205
Note: 1. See “About code examples” on page 17.
20.6 Data Transfer
Using the USART in MSPI mode requires the Transmitter to be enabled, that is, 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 writing to the UDRn
I/O location. This is the case for both sending and receiving data since the transmitter controls the transfer
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;
}