Hi Jenny,

I read and reread your problem description quite a few times. Is this what you're trying to do? (Bear with me, I'm kinda slow sometimes.)

Send a byte from a PC to the uC over a serial bus.

uC waits for reception of this byte before initiating polling of compass chip via a different port.

Retrieved information from compass is returned to PC through UART over serial bus.

OK. If the PC and uC aren't talking:

Are serial interrupts enabled?
Is serial receive enabled?
Are baud rates set correctly?
Do you need a null-modem cable?
Do you have access to a oscope?

You can verify that serial data is being received on the correct pin, and you can wiggle a port pin to indicate that serial interrupts are occurring. An LED appropriately connected to a port pin can help debug as well, but remember you won't see it blink at serial data rates.

Dennis