The flexibility of the DDS is somewhat comprimised by the need to edit and recompile a program whenever we want to change its output frequency. Since the serial port on our CPU module is currently unused, an obvious solution to this shortcoming would be to allow the frequency to be set by typing it on the keyboard. More elaborate user interfaces are possible, using Labview or your favorite graphics toolkit, but they will all have to utilize the serial interface, since that's our only way into the CPU.
So here is your programming challenge: Write a program for the MSP430/AD9851 combination which will accept a frequency via the serial port and produce that frequency as it output until a new frequency is entered.