Atmega128(l) – Rainbow Electronics ATmega128L User Manual
Page 159
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ATmega128(L)
2467B–09/01
The following code examples show how to initialize the SPI as a master and how to per-
form a simple transmission. DDR_SPI in the examples must be replaced by the actual
data direction register controlling the SPI pins. DD_MOSI, DD_MISO and DD_SCK
must be replaced by the actual data direction bits for these pins. E.g. if MOSI is placed
on pin PB5, replace DD_MOSI with DDB5 and DDR_SPI with DDRB.
Note:
1. The example code assumes that the part specific header file is included.
Assembly Code Example
SPI_MasterInit:
; Set MOSI and SCK output, all others input
ldi
r17,(1<<DD_MOSI)|(1<<DD_SCK)
out
DDR_SPI,r17
; Enable SPI, Master, set clock rate fck/16
ldi
r17,(1<<SPE)|(1<<MSTR)|(1<<SPR0)
out
SPCR,r17
ret
SPI_MasterTransmit:
; Start transmission of data (r16)
out
SPDR,r16
Wait_Transmit:
; Wait for transmission complete
sbis
SPSR,SPIF
rjmp
Wait_Transmit
ret
C Code Example
void SPI_MasterInit(void)
{
/* Set MOSI and SCK output, all others input */
DDR_SPI = (1<<DD_MOSI)|(1<<DD_SCK);
/* Enable SPI, Master, set clock rate fck/16 */
SPCR = (1<<SPE)|(1<<MSTR)|(1<<SPR0);
}
void SPI_MasterTransmit(char cData)
{
/* Start transmission */
SPDR = cData;
/* Wait for transmission complete */
while(!(SPSR & (1<<SPIF)))
;
}