I am having trouble configuring Arduino Due SPI to an ADC. Here is a link to the ADC: https://www.analog.com/media/en/technical-documentation/data-sheets/AD7490.pdf

Here is how I have the pins connected: 
+3.3V > 7490 pin 22 Vin 
+3.3V > 7490 Vref 
DUE CS (8) > 7490 pin 20 SS - slave select)
 DUE SCK > 7490 pin 16 (SCK - clock)
 DUE MOSI > 7490 pin 19 (MOSI - data out)
 Ground > 7490 pin 24( all gnds tied together
DUE MISO > 7490 pin 15 

Below is my code, I feel like I am writing the correct bits into the register. The problem I think I'm having is getting the timing write. The code is a simple attempt to read a single channel. 

    #include <SPI.h>

    // Set Constants
    const int adcChipSelectPin = 8;      // set pin 8 as the chip select for the 
    ADC:

    // Start setup function:
    void setup() {

    pinMode (adcChipSelectPin, OUTPUT);
    // set the ChipSelectPins high initially:
    digitalWrite(adcChipSelectPin, HIGH);
    // initialise SPI:
    SPI.begin();
    SPI.setBitOrder(MSBFIRST);         // Not strictly needed but just to be 
    sure.
    SPI.setDataMode(SPI_MODE0);        // Not strictly needed but just to be 
    sure.
    Serial.begin(9600);
    //Clock Speed: Master clock/divider
    //84Mhz/64 =  1.3 MHz
    SPI.setClockDivider(SPI_CLOCK_DIV64);
  
    } // End setup function.

    // Start loop function:
    void loop() {
    float voltage[2];
    for (int i = 0; i < 3; i++) {
    voltage[i] = readAdc(0, 0);
    }
  
 
    }// End of loop function.

    //Function to read the ADC, accepts the channel to be read.
    float readAdc(int channel, int slave) {

    float value;
    if (slave == 0) {
    noInterrupts(); // disable interupts to prepare to send address data to the 
    ADC.
    digitalWrite(adcChipSelectPin, LOW); // take the Chip Select pin low to 
    select the ADC.
    
   
    byte FirstByte = 0b10000011;  // b00000111 Isolates the three LSB.  
    byte SecondByte = 0b00110000;      // b00001111 isolates the 4 LSB for the 
    value returned.

    SPI.transfer(FirstByte);

    byte response1 = SPI.transfer(SecondByte);
    byte response2 = SPI.transfer(0x00);
    
    digitalWrite(adcChipSelectPin, HIGH); // take the Chip Select pin high to 
    de-select the ADC.
    interrupts(); // Enable interupts.
    Serial.println(response1);
    Serial.println(response2);
    
  }


Any pointers are appreciated. 

Cheers!