Have you tried your code in the simulator? As posted, your code is difficult to read and there are a number of suspect lines.

You do this a lot:

(4.548e6/frequency). Remember you're only using integer operations, so will the result be what you expect?


Keil has function for 'atol' ascii to long conversion and probably a gets function to get a string from the serial port. This should simplify your code a bit.

When posting code, use the 'insert code' button so that the code formatting is kept.