ADS1243-HT No Response

Hi all.

I'm trying to use the ADS1243-HT in my senior design project and I have a few questions about how we have the device currently set up.  Right now I'm sending it the SELFCAL command via SPI from an MSP430F2619S-HT microcontroller, and DRDY is not being pulled low by the ADC, which should indicate that the calibration has completed.  Here's how we setup our hardware.

The DRDY and *CS pins are connected to GPIO pins (interrupt capable for DRDY), and the SPI lines are tied to the outputs of a USCI module in SPI mode.  The ADC is being run at 4.9152MHz (MCLK) to achieve the maximum 30Hz conversion rate, and the serial communications are being clocked at 1.0488MHz (MCLK/4).  

We are only sampling the voltage of two RTD sensors with an output range of 0V to +3.3V.  The reference voltage is +1.65V and any differential pair will be sampled with the negative channel tied to +1.65V to give a fullscale reading at +3.3V and a negative fullscale reading at 0V.

Below is a shot of the output from our MSP430.  

I'll also share some of my code.

void main()
{
	 /***********************************************
	 *	 			    ADC TEST				    *
	 ***********************************************/

	 	 ADC_Calibrate();


	 	 while(!conversion_ready);		// Wait for calibration to complete
	 	 conversion_ready = false;		// Clear DRDY flag

	 	 ADC_Write_Reg(ACR, 0x00, 0x00);

	 	 SamplePair = Select_Fullscale;
	 	 ADC_Set_Mux(SamplePair);

	 	 while(!conversion_ready);		// Wait for calibration to complete
	 	 SamplePair = Select_Ground;
	 	 ADC_Set_Mux(SamplePair);
	 	 test = ADC_Read_Conversion();

	 	 while(!conversion_ready);		// Wait for calibration to complete
	 	 SamplePair = Select_Midscale;
	 	 ADC_Set_Mux(SamplePair);
	 	 test = ADC_Read_Conversion();

	 	 while(!conversion_ready)
	 	 test = ADC_Read_Conversion();
}

uint8_t spiSendByte(uint8_t data)
{
    while (!(SPI_IFG & SPI_TXIFG));		// USCI_B1 TX buffer empty?
    SPI_TXBUF = data;    			// write
    while (!(SPI_IFG & SPI_RXIFG)); 		// wait for transfer to complete
    return(SPI_RXBUF);
}

void ADC_Calibrate()
{
     ADC_CommandByte command = SelfCal;

     P4OUT = 0x40;			         // Set ADC Chip Select Low
     spiSendByte(command);
     P4OUT |= ADC_CS;			         // Set ADC Chip Select High
}

void ADC_Set_Mux(ADC_SelectMux SelectLine)
{
     uint8_t NumRegs = 0;

     switch(SelectLine)
     {
          case Select_IntTemp_Sensor: //Select Internal Temperature Sensor
               ADC_Write_Reg(MUX, NumRegs, 0x12);  // Debug Voltage Pair
               break;
          case Select_ExtTemp_Sensor: //Select External Temperature Sensor
               ADC_Write_Reg(MUX, NumRegs, 0x60);
               break;
          case Select_ExtPress_Sensor: //Select External Pressure Sensor
               ADC_Write_Reg(MUX, NumRegs, 0x80);
               break;
          case Select_OffsetCal_Pair: //Select External Pressure Sensor
               ADC_Write_Reg(MUX, NumRegs, 0x72);
               break;
          case Select_GainCal_Pair: //Select External Pressure Sensor
               ADC_Write_Reg(MUX, NumRegs, 0x32);
               break;
          case Select_Fullscale:
               ADC_Write_Reg(MUX, NumRegs, 0x01);
        	   break;
          case Select_Midscale:
        	   ADC_Write_Reg(MUX, NumRegs, 0x10);
        	   break;
          case Select_Ground:
        	   ADC_Write_Reg(MUX, NumRegs, 0x00);
        	   break;
          default:
               //ERROR CASE
        	  break;
     }
}

void ADC_Write_Reg(ADC_CommandByte address, uint8_t NumRegs, uint8_t data)
{
     int x;
     uint8_t com_and_address;
     ADC_CommandByte command = WriteReg;
     
     com_and_address = command + address;       // combine register address and command
     P4OUT = 0x40;
     spiSendByte(com_and_address);
     spiSendByte(NumRegs);
     
     for(x = 0; x <= NumRegs; x++)
          spiSendByte(data & 0xFF);             // masking all but lower 8 bits
     P4OUT |= ADC_CS;
}

uint32_t ADC_Read_Conversion()
{
     extern bool conversion_ready;
     ADC_CommandByte command = ReadData;
     uint8_t in_data[3];
     uint32_t out_data;
     uint8_t x;

     P4OUT = 0x40;
     spiSendByte(command);
     spiReadFrame(in_data, 3);

     for(x = 0; x < 2; x++)
    	 out_data |= in_data[x]  << (8 * x);

     P4OUT |= ADC_CS;
     conversion_ready = false;			//reset conversion ready flag

     return out_data;
}