Hi Matt,

My first suggestion would be go to http://www.keil.com and download their free evaluation 8051 development software. It's limited, but should be more than sufficient for your needs. And it has some pretty great debugging features. You will be able to run/step your code while watching all of the pertinent registers.

Now about your code above. Is that the whole program, or did you leave out some things for brevity's sake? Understand that I do this sort of thing with assembler, not C++, so I may be completely off about this. Still, I'm wondering how the compiler knows where, in memory, to put the ISR. I don't remember where it is off the top of my head, but there is a fixed memory location the µ-controller transfers control to upon either TI or RI being triggered. Does your compiler know where to put the ISR? It can't just go anywhere. While you're reading, check out the tutorial on this site. It does a pretty good job of explaining (with examples) what you have to do to use UART ISRs.