F28027 Piccolo SPI Problem

Other Parts Discussed in Thread: DAC8871

I'm using the SPI to communicate with the DAC8871. If I write to the SPITXBUF register it looses the MSB and therefore I can only count to 32767 instead of 65535. I have a global variable, volatile unsigned int DAC_value, and a function, DAC_update(void), that sends the value over the SPI. By using the global variable I loose the MSB. If I make a temp variable inside DAC_update(void) and send that, just to test it, it works fine.

Code:

void DAC_update(void)
{
    while(SpiaRegs.SPISTS.bit.BUFFULL_FLAG != 0);

    SpiaRegs.SPITXBUF = (unsigned int) DAC_value;   
}

inside an timer interrupt:

if(DAC_value > 65000)
        DAC_value = 0;
else
        DAC_value += 10;   

DAC_update();

If I change the update function to that below it send the full value and the DAC outputs the maximum value.

void DAC_update(void)
{

    unsigned int data = 65535;
    while(SpiaRegs.SPISTS.bit.BUFFULL_FLAG != 0);

    SpiaRegs.SPITXBUF = data;   
}