DAC1282: Register readback failed

Hi team,

Here's an issue from the customer may need your help:

The DAC1282 output DC voltage is controlled using the TMS320F28379D with SPI communication, SPICLK and SPISIMO are normal according to the oscilloscope as the following figure, with a period of 12.5us. 

But SPISOMI is always low and the debug interface is unable to read the value of SPISOMI. Please see the below program:

/*
 * DAC read debug 
 *
 */

#include "F28x_Project.h"

typedef unsigned char Uint8;


//Notice 
void gpio_init();//Configure all GPIO ports to the PCB board (including 3-wire SPI) 
void spia_init();
void dac_init();
void spia_xmit(Uint8 a);

Uint8 rdata;

void main()
{
    //Initialization 
    InitSysCtrl();//System control 
    InitGpio();//GPIO
    DINT;//Turn off the interrupt 
    InitPieCtrl();//PIE control registers 
    IER = 0x0000;//The interrupt flag bit is cleared 
    IFR = 0x0000;//The interrupt flag bit is cleared 
    InitPieVectTable();//Interrupt vector table 


    gpio_init();//Configure all GPIO ports to the PCB board (including 3-wire SPI) 
    spia_init();
    dac_init();

    spia_xmit(0x20);//Read the GANMOD register address 
    DELAY_US(100);
    spia_xmit(0x00);//Read a register 
    DELAY_US(100);
    while(SpiaRegs.SPISTS.bit.INT_FLAG != 1){}
    rdata = SpiaRegs.SPIRXBUF;







}

void gpio_init()
{
    /* GPIO connection port                           I/O        The initial value 
     * 111  GPIO_CS_DA     O          0
     * 60   SPICLKA_DA     SPIA CLK
     * 59   SPISOMIA_DA    SPIA SOMI
     * 58   SPISIMOA_DA    SPIA SIMO
     * 22   GPIO_SW/TD_DA  O          0
     */

    EALLOW;

    //CS、SW/TD、RESET、DRDY
    GpioCtrlRegs.GPDPUD.bit.GPIO111 = 0;
    GpioCtrlRegs.GPDMUX1.bit.GPIO111 = 0;
    GpioCtrlRegs.GPDDIR.bit.GPIO111 = 1;
    GpioDataRegs.GPDCLEAR.bit.GPIO111 = 1;//GPIO_CS_DA

    GpioCtrlRegs.GPAPUD.bit.GPIO22 = 0;
    GpioCtrlRegs.GPAMUX2.bit.GPIO22 = 0;
    GpioCtrlRegs.GPADIR.bit.GPIO22 = 1;
    GpioDataRegs.GPACLEAR.bit.GPIO22 = 1;//GPIO_SW/TD_DA

    //SPI
    //DA（Enable, Asynchronous, SPI) 
    GpioCtrlRegs.GPBPUD.bit.GPIO60 = 0;
    GpioCtrlRegs.GPBQSEL2.bit.GPIO60 = 3;
    GpioCtrlRegs.GPBMUX2.bit.GPIO60 = 3;
    GpioCtrlRegs.GPBGMUX2.bit.GPIO60 = 3;//SPICLKA_DA

    GpioCtrlRegs.GPBPUD.bit.GPIO59 = 0;
    GpioCtrlRegs.GPBQSEL2.bit.GPIO59 = 3;
    GpioCtrlRegs.GPBMUX2.bit.GPIO59 = 3;
    GpioCtrlRegs.GPBGMUX2.bit.GPIO59 = 3;//SPISOMIA_DA

    GpioCtrlRegs.GPBPUD.bit.GPIO58 = 0;
    GpioCtrlRegs.GPBQSEL2.bit.GPIO58 = 3;
    GpioCtrlRegs.GPBMUX2.bit.GPIO58 = 3;
    GpioCtrlRegs.GPBGMUX2.bit.GPIO58 = 3;//SPISIMOA_DA

    EDIS;

}

void spia_init()
{
    //DAC1282 clock polarity (CPOL) is 0 and the clock phase (CPHA) is 0 
    //configure control register（8-bit reserved，0000 0000 0000 0111 = 0x0007）
    SpiaRegs.SPICCR.bit.SPISWRESET = 0;//SPI reset
    SpiaRegs.SPICCR.bit.CLKPOLARITY = 0;//clock polarity is 0（SCK idle is low）
    SpiaRegs.SPICCR.bit.HS_MODE = 0;//Turns off high-speed mode 
    SpiaRegs.SPICCR.bit.SPILBK = 0;//Turn off loopback mode 
    SpiaRegs.SPICCR.bit.SPICHAR = (8-1);//Word length 8 bits 

    //Run control registers (11-bit reserved，0000 0000 0000 0110 = 0x0016）
    SpiaRegs.SPICTL.bit.OVERRUNINTENA = 1;//The receive overflow interrupt is disabled 
    SpiaRegs.SPICTL.bit.CLK_PHASE = 0;//The clock phase is 0 (sampled on the first transition edge）
    SpiaRegs.SPICTL.bit.MASTER_SLAVE = 1;//MCU host
    SpiaRegs.SPICTL.bit.TALK = 1;//Master transmit is enabled 
    SpiaRegs.SPICTL.bit.SPIINTENA = 0;//SPI interrupts are disabled

    //SpiaRegs.SPISTS.all = 0;

    //Baud rate register (9-bit reserved，0000 0000 0000 007C）
    /*
     * LSPCLKfreq=CPUfreq/n //(n=1,2,4,6,8,10,12,14)
     * SPI Baud Rate=LSPCLKfreq/(SPIBRR+1)
     * Without adding an external auxiliary clock 
* The F28379D has a CPU frequency of 10 MHz, which corresponds to a minimum low-speed peripheral clock of 715 KHz and a minimum baud rate of 5586 SPS 
* This minimum baud rate is greater than the maximum baud rate of 4000 SPS when FIR filter mode is selected 
* Therefore, the sinc filter mode is selected with the baud rate set to 8000 SPS, divide by 10, SPIBRR = 124 = 0x007C 
     */

    EALLOW;
    ClkCfgRegs.LOSPCP.all = 0x0005;//101（10分频）
    EDIS;

    SpiaRegs.SPIBRR.bit.SPI_BIT_RATE = 0x007C;

    //Priority control register 
    SpiaRegs.SPIPRI.bit.FREE = 1;//Free to run during emulation, pause on breakpoint does not stop the SPI 

    //Stop SPI software reset to be ready for receive or transmit 
    SpiaRegs.SPICCR.bit.SPISWRESET = 1;
}


    //2、External component initial configuration（DAC、ADC）

void dac_init()
{
    spia_xmit(0x40);//Write the GANMOD register address 
    DELAY_US(100);
    spia_xmit(0x00);//write a register
    DELAY_US(100);
    spia_xmit(0x0D);//write 0000 1101，GAIN=8，DC mode
    DELAY_US(100);



    //The SINEG register is not configured 

    spia_xmit(0x42);//Write the SWM register address 
    DELAY_US(100);
    spia_xmit(0x00);//write a register
    DELAY_US(100);
    spia_xmit(0x10);//write 0001 0000，switches are fully open for differential 
    DELAY_US(100);

    //N registers are not configured 

    spia_xmit(0x44);//Write the DCG register address 
    DELAY_US(100);
    spia_xmit(0x02);//write three registers 
    DELAY_US(100);
    spia_xmit(0xE9);//DCG0
    DELAY_US(100);
    spia_xmit(0x26);//DCG1
    DELAY_US(100);
    spia_xmit(0x31);//DCG2
    DELAY_US(100);

    //PULSE register is not configured 
}


void spia_xmit(Uint8 a)
{
    SpiaRegs.SPITXBUF = (Uint16)(a<<8);//Transfers 8-bit data to the serial transmit buffer 
}

Could you help check this case? Thanks.

Best Regards,

Cherry