Common Functionalities

The functionalities of the AVR Dx SPI peripheral in Host/Client mode are similar to ATmega128 when Normal mode is used, but the register names and bit order can be different. The following table shows the mapping of the megaAVR SPI configuration bits into the AVR Dx SPI register structure:

megaAVR® AVR® Dx Description
SPCR.DORD SPI.CTRLA.DORD SPI Data order
SPCR.MSTR SPI.CTRLA.MASTER Host/Client Select
SPCR.CPOL SPI.CTRLB.MODE[1:0] SPI Mode Select
SPCR.CPHA
SPCR.SPR1 SPI.CTRLA.PRESC[1:0] SPI Clock Prescaler (divider)
SPCR.SPR0
SPSR.SPI2X SPI.CTRLA.CLK2X Clock Double
SPCR.SPE SPI.CTRLA.ENABLE SPI Enable
SPCR.SPIE SPI.INTCTRL.IE SPI Interrupt Enable
SPSR.SPIF SPI.INTFLAGS.IF SPI Interrupt Flag
SPSR.WCOL SPI.INTFLAGS.WRCOL Write Collision Flag
SPDR SPI.DATA SPI Data Register

Another difference between families is the I/O pin configuration for use with the SPI peripheral. The megaAVR needs a proper configuration of used pins, while AVR Dx devices overwrite the I/O pin functionality when the pin is used by the SPI peripheral. Refer to the Pin Override section for details.

The following code snippets show initialization of the SPI peripheral in Host mode:

megaAVR® - SPI Initialization in Host Mode

voidSPI_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);}voidSPI_MasterTransmit(char cData){/* Start transmission */
    SPDR = cData;/* Wait for transmission complete */while(!(SPSR &(1<<SPIF)));}

AVR® Dx - SPI Initialization in Host Mode

voidSPI0_init(void){
    PORTA.DIR &=~PIN4_bm;/* Set MOSI pin direction to input */
    PORTA.DIR |= PIN5_bm;/* Set MISO pin direction to output */
    PORTA.DIR &=~PIN6_bm;/* Set SCK pin direction to input */
    PORTA.DIR &=~PIN7_bm;/* Set SS pin direction to input */
    SPI0.CTRLA = SPI_DORD_bm        /* LSB is transmitted first */| SPI_ENABLE_bm     /* Enable module */&(~SPI_MASTER_bm);/* SPI module in Client mode */}

uint8_t SPI0_exchangeData(uint8_t data){
    SPI0.DATA = data;while(!(SPI0.INTFLAGS & SPI_IF_bm))/* waits until data is exchanged*/{;}return SPI0.DATA;}
Parent topic: SPI