2.7.1 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	SPI.CTRLB.MODE[1:0]	SPI Mode Select
SPCR.SPR1	SPI.CTRLA.PRESC[1:0]	SPI Clock Prescaler (divider)
SPCR.SPR0	SPI.CTRLA.PRESC[1:0]	SPI Clock Prescaler (divider)
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

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)))
    ;
}

AVR® Dx - SPI Initialization in Host Mode

void SPI0_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;
}