ADS1255. Spontaneous resets while data receiving

Other Parts Discussed in Thread: ADS1255

Hello!

Currently I am studying ADC ADS1255 using stm32 with chibios. I have developed a prototyping board for the ADC . Board contains the power supplies of analog and digital parts ( 5 V, as the reference 2.5V and 3.3V ). XTAL 8 MHz 10ppm. Scheme is represented below

I have carefully studied the datasheet and wrote a minimally functional program that performs the following tasks:

1) Power up sequence;

2) Reset sequence;

3) ADC configuration;

4) Data receiving.

Here is the code:

// Sending command to ADC
void ads_command(uint8_t command) {
    CsLo();                              // Chip select low
    uint8_t temp = command;
    spiSend(SPI_Driver, 1, &temp);       // spiSend is chibiOS's function, that send n bytes (1 in this function) from the variable "temp"
    CsHi();                              // Chip select high
  }

// Reset ADC
void ads_reset(void) {
  ads_command(ADS125X_RESET);
  chThdSleepMilliseconds(MS2ST(4));      // 4 ms delay
  ads_command(ADS125X_SELFCAL);
  chThdSleepMilliseconds(MS2ST(10));     // 10 ms delay
}

// Wakeup ADC from Standby
void ads_wakeup(void) {
  ads_command(ADS125X_WAKEUP);
}

// Write data to ADC's register
void ads_wreg(uint8_t firstreg, uint8_t numreg) {
  uint8_t temp = ADS125X_WREG + firstreg;
  CsLo();
  spiSend(SPI_Driver, 1, &temp);
  temp = numreg-1;
  spiSend(SPI_Driver, 1, &temp);
  spiSend(SPI_Driver, numreg, &regstack);         // regstack - is a global array (length 0x0A) for ADC's reg data collection
  CsHi();
}

//Read data from ADC's register
void ads_rreg(uint8_t firstreg, uint8_t numreg) {
  uint8_t temp = ADS125X_RREG + firstreg;
  CsLo();
  spiSend(SPI_Driver, 1, &temp);
  temp = numreg-1;
  spiSend(SPI_Driver, 1, &temp);
  chThdSleepMilliseconds(MS2ST(2));
  spiReceive(SPI_Driver, numreg, &regstack);
  CsHi();
}

void ads_rdatac() {
  PWaitingThread = chThdGetSelfX();
  chSchGoSleepS(CH_STATE_SUSPENDED);
  ads_command(ADS125X_RDATAC);
}

void ads_sdatac() {                         
  PWaitingThread = chThdGetSelfX();        
  chSchGoSleepS(CH_STATE_SUSPENDED);       
  ads_command(ADS125X_SDATAC);
}

// Read ADC's conversion data in continuous mode
void read_data(uint8_t numdata, void *pbuff) {
  CsLo();
  for (uint8_t i=1; i < numdata+1; i++) {
    PWaitingThread = chThdGetSelfX();              // Here is a routine that wainting for external event (DRDY changing from high to low)
    chSchGoSleepS(CH_STATE_SUSPENDED);             // to perform read operation 
    spiReceive(SPI_Driver, 3, pbuff);
    pbuff = pbuff + 3;
  }
  CsHi();
}

// One shot mode
void read_data_oneshot(uint8_t numdata, void *pbuff) {
  ads_sdatac();
  for (uint8_t i=1; i < numdata+1; i++) {
    PWaitingThread = chThdGetSelfX();
    chSchGoSleepS(CH_STATE_SUSPENDED);
    ads_command(ADS125X_RDATA);
    CsLo();
    spiReceive(SPI_Driver, 3, pbuff);
    pbuff = pbuff + 3;
    CsHi();
  }
}

void ads_conf() {
  ads_rreg(0,1);                                   // read status
  regstack[0] = regstack[0] | ADS125X_BUFON;       // Change reg value
  ads_wreg(0,1);                                   // Buff on

  regstack[0] = 0x01;                              // Positive - AIN0
  ads_wreg(0x01, 1);                               // Negative - AIN1 differential mode

  regstack[0] = 0xB0;
  ads_wreg(0x03,1);                                // Sampling speed 2 kSPS

  ads_rreg(0x02,1);
  regstack[0] = regstack[0] | 0x00;                //  PGA = 1
  ads_wreg(0x02,1);

  ads_command(ADS125X_SELFCAL);                    // Self calibration
  chThdSleepMilliseconds(MS2ST(2));
}

/*
 * Threads
 */

int main(void) {


  halInit();
  chSysInit();
/*
 * GPIO configuration
 */

  palSetPadMode(GPIOSPI, CS, PAL_MODE_OUTPUT_PUSHPULL);   /*  CS  */
  palSetPadMode(GPIOSPI, SCK, PAL_MODE_ALTERNATE(5) | PAL_STM32_OSPEED_HIGHEST |GPIO_MODER_MODER5_1);  /*   SCK */
  palSetPadMode(GPIOSPI, SO, PAL_MODE_ALTERNATE(5) | GPIO_MODER_MODER6_1);  /*  MISO    */
  palSetPadMode(GPIOSPI, SI, PAL_MODE_ALTERNATE(5) | PAL_STM32_OSPEED_HIGHEST | GPIO_MODER_MODER7_1);  /*   MOSI    */

  palSetPadMode(GPIOC, 10, PAL_MODE_ALTERNATE(7));       // TX
  palSetPadMode(GPIOC, 11, PAL_MODE_ALTERNATE(7));      // RX

 /*
  * Drivers starting
  */
  uartStart(&UARTD3, &uart_cfg);
  spiStart(SPI_Driver, &spicnfg);
  extStart(&EXTD1, &extcfg);


  ads_reset();                                 // ADC reset
  ads_conf();                                  // Configure 
  //ads_rdatac();                              // Dont used in one shot mode

  while (true) {
    //read_data(30, &inbuff);                  // Donnt used in one shot mode
    read_data_oneshot(30, &inbuff);            // Perform data receiving
    uartStartSend(&UARTD3, 90, &inbuff);       // Sending data to computer for debug purpose
  }
}

Here is logic oscillogram, that shows properly configuration o SPI and ADC (its saleae logic oscillogram with 10 sec length. Its difficult to make screenshot, that provide detailed information about signals). If there is no possibility to open then I'll send a screenshot.

16 MHz, 160 M Samples [22].rar

PROBLEM.

If you look at the trace, you may notice that after 360 ms there is a spontaneous reset. It occurs in different times, and only when reading data. If you configure the ADC and read the data, this is not a problem. The following waveform data without reading.

16 MHz, 160 M Samples [23].rar 

On the last waveform reset does not occure.

As this problem occurs when any attempt to change source at the input. I have suggested that it may be either a defense mechanism within the ADC from the ESD or any another overvoltage, but I did not find anything in the datasheet.

Please any help in solving the mystery. Thank you!

With respect,

Maslov Artem