Maybe you're beyond this point already, but maybe not. I wonder if you might learn something by backing up a step and trying something really, really, really simple. A quick little test like the following might be worth the effort.

If it runs as expected, great -- use it as a starting point to build towards what you want. If it doesn't, then you know that your problems don't have anything to do with the serial port and that you should focus your attention elsewhere.

-- Russ

/*  Square-one test program to see if anything works at all.  Puts
    a recognizable waveforem on P1.0 that should be perfectly
    stable and look something like this:
    __    __    _______    __    _______    __    _______
      |__|  |__|       |__|  |__|       |__|  |__|       

*/


#define GREEN_LED       0x01    // Green LED is on bit 0 of P1

main() {
    while (1) {                 // Repeat forever
        P1 &= ~GREEN_LED;       // Green LED on
        P1 |=  GREEN_LED;       // Green LED off
        P1 &= ~GREEN_LED;       // Green LED on
        P1 |=  GREEN_LED;       // Green LED off

        P1 |=  GREEN_LED;       // Wait a short while
        P1 |=  GREEN_LED;
        P1 |=  GREEN_LED;
        P1 |=  GREEN_LED;
        }                       // End 'repeat forever'
    }                           // End main()