ADS7843 Touch Screen Controller with SPI - data problem

[Micro9900]

Hey guys I'm having a bit of trouble understanding the data I am receiving. I took a bit of time to do the other portions of my project and then came back to the touch screen. So far, I am able to read data upon the second pass through for x and y. The main problem is that the expected values should be up to 12 bits of data (max 4096), and instead I am reading values as high a 32,000.

I am using unsigned shot (UINT16) to read the data from the 16bit SPI receive buffer. The good news is that as I press up, down, left, or right, the values do increase/decrease (sometimes it can be glitchy and it gives me a lower value when I am expecting to read a higher one).

Datasheet for ADS7843

I am using C32, MPLAB X, and a pic32mx795F512H. Here is my code:

void Touch_Init(void)		// Initialises the touch screen
{
	Touch_CS = 1;				// Deasserts the CS line.
	Touch_PenIRQ_TRIS = 1;

        // Initialize SPI hardware module pg. 206/314 of C32 user guide
        // SPI Channel (set to 4), Set uC as Master, clock polarity cotrol, baud rate
        // Baud Rate = BR = Fpb/(2*(SPIBRG+1)), Fpb is 1:1 => 80MHz
        // Baud RAte = 80MHz/(2*(2MHz+1))=>20
        SpiChnOpen(SpiChn, SPICON_MSTEN|SPICON_CKP|SPICON_MODE16|SPICON_ON,20);

	Touch_CS = 0;
        TDelay(); //200ns

        // See pg. 6 and 9 of 18 in ADS7843 datasheet/ pg.21 of XPT2046
        // S = start bit, A=addressing-input for multiplexer, MODE=selects ADC resolution PD = power down bits for idle
        // Bits 0 -> 7 = S A2 A1 A0 MODE SFR/DFRnot PD1 PD0
	SpiChnPutC(SpiChn, 0b10010100);				// Sends the initialisation byte
        dummyReadSPI=SPI4BUF;                                       // clears the receive buffer
	Touch_CS = 1;
}

void ReadTouchXY(void)
{
    UINT16 readX, readY,sampleCount=0,avgCount=0; 
	
		Touch_PenIRQ_TRIS = 0;                          // Sets the PenIRQ to an output
		Touch_PenIRQ_LAT = 0;                           // Drives the PenIRQ low so the diode is not forward biased

		Touch_CS = 0;
                TDelay();                                       // Asserts the CS line and gives a required delay

                // Read twice to ensure data is recieved
                for(sampleCount=1;sampleCount<=6;sampleCount++)
                {
                    SpiChnPutC(SpiChn, 0b11010100);	   // Sends the control byte
                    SpiChnGetC(SpiChn);                             // Reads the dummy data to clear the receive buffer
       
                    SpiChnPutC(SpiChn, 0x00);                   // Sends a dummy byte in order to clock the data out
                    readY = SpiChnGetC(SpiChn);               // Reads Y coordinates
          
                    SpiChnPutC(SpiChn, 0b10010100);      // Sends the next control byte to read the other axis
                    readX = SpiChnGetC(SpiChn);              // Reads X coordinates
                }
                
                coordXresult=readX;
                coordYresult=readY;

             

		Touch_CS = 1;                                           // Deasserts the chip select line

		Touch_PenIRQ_TRIS = 1;					// Sets the PenIRQ to an input again

}

I also have a 200ms delay after I read to prevent the interrupt from the ADS7843 from triggering again. However, if it is held down longer it triggers the interrupt again.


Basically my questions are as follows:
_____________________________
1. Why am I getting higher values (higher than 4096) when I receive the 12bit data?
2. Is there anything that I am forgetting/not including when reading/writing to the ADS7843?

Thank you.