ADS1263: DOUT/DRDY stuck at 0

Hello,

I am trying to write and read from the ADS1263 SPI using the STM32F437 processor but the data I get on the DOUT/DRDY is always 0.

The SPI setting I use is:

SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge; 
SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_8; 
SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
SPI_InitStructure.SPI_CRCPolynomial = 7;

The SCLK frequency is 6 MHz (48 M / 8).

To read a register I use the following code:

adc_in[0] = ADS1263_RREG_CMD + REGX    // REGX = 0 .. 26
adc_in[1] = 0;
SPI_ADC_ReadReg(adc_in, adc_out);

The function SPI_ADC_ReadReg look like this:

void SPI_ADC_ReadReg(u8 u8 *adc_in, u8 *adc_out)
{

/* Loop while DR register in not emplty */
while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_BSY) == SET);

/* Select the ADC: Chip Select low */
SPI_ADC_CS1_LOW;
for (int i=0; i<3+adc_in[1]; i++)
{

/* Send Half Word through the SPI2 peripheral */
SPI_I2S_SendData(SPI1, adc_in[i]);

/* Loop while DR register in not emplty */
while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE) == RESET);
}

/* Wait to receive a byte */
while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE) == RESET);

/* Loop while DR register in not emplty */
while (SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_BSY) == SET);

/* Return the Half Word read from the SPI bus */
adc_out[0] = SPI_I2S_ReceiveData(SPI1);

/* Deselect the ADC: Chip Select low */
SPI_ADC_CS1_HIGH;
}

 On a logic scope all the signals - CS, SCLK and MOSI look OK. Only DOUT/DRDY is stuck at 0.

Can you tell me what I'm missing?

Thanks