Atmel ATmega128, Manual

Page: 166 / 386

166
2467S–AVR–07/09
ATmega128
The following code examples show how to initialize the SPI as a slave and how to perform a sim-
ple reception.
Note: 1. See “About Code Examples” on page 9.
Assembly Code Example
(1)
SPI_SlaveInit:
; Set MISO output, all others input
ldi r17,(1<<DD_MISO)
out DDR_SPI,r17
; Enable SPI
ldi r17,(1<<SPE)
out SPCR,r17
ret
SPI_SlaveReceive:
; Wait for reception complete
sbis SPSR,SPIF
rjmp SPI_SlaveReceive
; Read received data and return
in r16,SPDR
ret
C Code Example
(1)
void SPI_SlaveInit( void )
{
/* Set MISO output, all others input */
DDR_SPI = (1<<DD_MISO);
/* Enable SPI */
SPCR = (1<<SPE);
}
char SPI_SlaveReceive( void )
{
/* Wait for reception complete */
while (!(SPSR & (1<<SPIF)))
;
/* Return data register */
return SPDR;
}