如何使用28069操作ADS1259？

我在项目中使用spib与ads1259链接，希望读出1259的9个寄存器的内容，可是没有成功。

我的程序如下：

main(){

.....

     spi_xmit(0x20);

    spi_xmit(0x08);

for( i=0;i<9;i++){

spi_xmit(0x00);
     while(SpibRegs.SPIFFRX.bit.RXFFST !=1) { }    
         rdata[i] = SpibRegs.SPIRXBUF;

        }

}

void spi_init()
{   
 SpibRegs.***.all =0x0007;              // Reset on, rising edge, 16-bit char bits 
 SpibRegs.***.all =0x0006;           // Enable master mode, normal phase,
                                                 // enable talk, and SPI int disabled.
 SpibRegs.SPIBRR =0x007F;         
    SpibRegs.***.all =0x0087;           // Relinquish SPI from Reset  
    SpibRegs.SPIPRI.bit.FREE = 1;                // Set so breakpoints don't disturb xmission
}

void spi_xmit(Uint16 a)
{

   a<<=8;
    SpibRegs.SPITXBUF=a;
}   

void spi_fifo_init()          
{
// Initialize SPI FIFO registers
    SpibRegs.SPIFFTX.all=0xE040;
    SpibRegs.SPIFFRX.all=0x2044;
    SpibRegs.SPIFFCT.all=0x0;
}