Reading from slave chip (ADS1293) through SPI

[Konrad213]

Hi everyone!

I'm trying to read a register from the ADS1293 chip by using SPI but have been stuck for a good two days. The very basic code I have is right below:

#define SPI_INSTANCE   0

static uint8_t tx;
static uint8_t rx;

static const nrf_drv_spi_t m_spi_master_0 = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE);

void ADS_init( void )
{
    nrf_drv_spi_config_t const spi_config =
    {
        .sck_pin        = 27,
        .mosi_pin       = 6,
        .miso_pin       = 42,
        .ss_pin         = 44,
        .irq_priority   = APP_IRQ_PRIORITY_LOW,
        .orc            = 0xFF,
        .frequency      = NRF_DRV_SPI_FREQ_4M,
        .mode           = NRF_DRV_SPI_MODE_0,
        .bit_order      = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST, 
    };
    ret_code_t err_code = nrf_drv_spi_init(&m_spi_master_0, &spi_config, NULL, NULL);
    //SEGGER_RTT_printf(0, nrf_strerror_get(err_code));
     
}

uint8_t Read_reg(uint8_t addr)
{ 
  tx = ADS1293_READ_BIT | addr;
  ret_code_t err_code = nrf_drv_spi_transfer(&m_spi_master_0, &tx, 1, &rx, 1);
  SEGGER_RTT_printf(0, nrf_strerror_get(err_code));
  return rx;
}

There are two things I'm not 100% sure about:

1) If the pins I'm using are correct. Is there any way to make sure that the pins I'm using are correct that is simpler than managing to read the register on the ADS? Here's how they are connected:

 NRF      ADS
P0.19 -> SDO
P0.20 -> SDI
P0.04 -> SCLK
P0.03 -> CSB

2) If the way I'm using nrf_drv_spi_transfer is correct for the ADS. If I understand correctly what's on page 37 in their documentation I should send in 8 bits and will receive 8 bits and I do this by sending in the uint8_t tx (address but set the first bit to 1) and uint8_t rx. 

When I do this I get the NRF_SUCCESS code but the data received is 0x00 and is supposed to be 0x02 for the register I'm trying. I'm really new to this so I have really no idea what I should be doing right now.

[hmolesworth]

You have the 'scope incorrectly set to the AC setting on both probes; change to DC ..for the slower clock speed also slow down the timebase to see the whole waveform. 50mSecs seems already very slow, what speed are the SPI clocks?

The Arduino is doing 2 separate SPI transactions of 1 byte each; you can do the same on the nRF by sending 2 messages of 1 byte each; the first would be the command and the second would clock out the response. Inefficient, but then you compare like with like and can increase the clock back to the same as Arduino.

[Konrad213]

Thanks again! I changed to DC and now I see that everything is the same for the Arduino and Nordic chip except for the SDO on the slave chip, nothing gets sent back from the ads for some reason when using the Nordic chip.

[NeMo93]

Hi, i am facing a similar problem while trying to set up the SPI connection between ads1293 and nrf52840. Did you figure out how to solve this issue? 

[Simonr]

Hi

This case is close to 4 years old at this point, so the chances you'll get a reply from anyone active in this ticket are not likely to reply. If you need technical support I'd recommend creating a separate ticket where you describe your problem in detail and it will be assigned to the correct person. You can link to this case if you think it's relevant as well.

Best regards,

Simon