Can't get my DAC(PT8211) to work correctly using a PIC32MX uc and SPI

Question

I'm just trying to learn to use external ADC and DAC (PT8211) with my PIC32MX534f06h.

So far, my code is just about sampling a signal with my ADC every time a timer-interrupt is triggered, then sending then same signal out to the DAC. The interrupt and ADC part works fine and have been tested independently, but the voltages that my DAC outputs don't make much sens to me and stay at 2,5V (it's powered at 0 - 5V).

I've tried to feed the DAC various values ranging from 0 to 65534 (16bits DAC so i guess it should be the expected range of the values to feed to it, right?) voltage stays at 2.5V.

I've tried changing the SPI configuration, using different SPIs (3 and 4) and DACs (I have one soldered to my pcb, soldered to SPI3, and one one breadboard, linked to SPI4 in case the one soldered on my board was defective). I made sure that the chip selection line works as expected. I couldn't see the data and clock that are transmissed since i don't have a scope yet.

I'm a bit out of ideas now.

Chip selection and SPI configuration settings


signed short adc_value;
signed short DAC_output_value;
int Empty_SPI3_buffer;

#define Chip_Select_DAC_Set() {LATDSET=_LATE_LATE0_MASK;}
#define Chip_Select_DAC_Clr() {LATDCLR=_LATE_LATE0_MASK;}

#define SPI4_CONF 0b1000010100100000 // SPI on, 16-bit master,CKE=1,CKP=0   
#define SPI4_BAUD 100 // clock divider

DAC output function

//output to external DAC
void DAC_Output(signed int valueDAC) {
    INTDisableInterrupts();
    Chip_Select_DAC_Clr();
    while(!SPI4STATbits.SPITBE);    // wait for TX buffer to empty 
    SPI4BUF=valueDAC;               // write byte to TX buffer 
    while(!SPI4STATbits.SPIRBF);    // wait for RX buffer to fill 
    Empty_SPI3_buffer=SPI4BUF;      // read RX buffer 
    Chip_Select_DAC_Set();
    INTEnableInterrupts();
}

ISR sampling the data, triggered by Timer1. This works fine. ADC_input inputs the data in the global variable adc_value (12 bits, signed)

//ISR to sample data 
void __ISR( _TIMER_1_VECTOR, IPL7SRS) Test_data_sampling_in( void)
{
    IFS0bits.T1IF = 0;
    ADC_Input();
    //rescale the signed 12 bit audio values to unsigned 16 bits wide values
    DAC_output_value = adc_value + 2048;  //first unsign the signed 12 bit values (between 0 - 4096, center 2048)
    DAC_output_value = DAC_output_value *16;  // the scale between 12 and 16 bits is actually 16=65536/4096
    DAC_Output(DAC_output_value);
 }

main function with SPI, IO, Timer configuration

void main() {

    SPI4CON = SPI4_CONF; 
    SPI4BRG = SPI4_BAUD;

    TRISE = 0b00100000;
    TRISD = 0b000000110100;
    TRISG = 0b0010000000;

    LATD = 0x0;
    SYSTEMConfigPerformance(80000000L);  //
    INTCONSET = _INTCON_MVEC_MASK;    /* Set the interrupt controller for multi-vector mode */

//  
    T1CONbits.TON = 0;              /* turn off Timer 1 */
    T1CONbits.TCKPS = 0b11;            /* pre-scale = 1:1 (T1CLKIN = 80MHz (?) ) */
    PR1 = 1816;                    /* T1 period ~ ?  */
    TMR1 = 0;                       /* clear Timer 1 counter */
//    
    IPC1bits.T1IP = 7;              /* Set Timer 1 interrupt priority to 7 */
    IFS0bits.T1IF = 0;              /* Reset the Timer 1 interrupt flag */
    IEC0bits.T1IE = 1;               /* Enable interrupts from Timer 1 */
    T1CONbits.TON = 1;              /* Enable Timer 1 peripheral */

    INTEnableInterrupts();

    while (1){ 



  }
}

I would expect to see the voltage at the ouput of my DAC to mimic those I put at the input of my ADC, instead the DAC output value is always constant, no matter what I input to the ADC

What am i missing? Also, when turning the SPIs on, should I still manually manage the IO configuration of the SDI SDO SCK pins using TRIS or is it automatically taken care of?

pm101 pm101 · Accepted Answer · 2019-06-07T21:06:38

First of all I agree that the documentation I first found for PT8211 is rather poor. I found extended documentation here. Your DAC (PT8211) is actually an I2S device, not SPI. WS is not chip select, it is word select (left/right channel). In I2S, If you are setting WS to 0, that means the left channel. However it looks like in the extended datasheet I found that WS 0 is actually right channel (go figure).

The PIC you've chosen doesn't seem to have any I2S hardware so you might have to bit bash it. There is a lot of info on I2S though ,see I2S bus specification .

There are some slight differences with SPI and I2C. Notice that the first bit is when WS transitions from high to low is the LSB of the right channel. and when WS transitions from low to high, it is not the LSB of the left channel. Note that the output should be between 0.4v to 2.4v (I2S standard), not between 0 and 5V. (Max is 2.5V which is what you've been seeing).

I2S

Basically, I'd try it with the proper protocol first with a bit bashing algorithm with continuous flip flopping between a left/right channel.

Can't get my DAC(PT8211) to work correctly using a PIC32MX uc and SPI

2 Answers

I2S