refresh rate updation

[any thing]

I have to actually change the scan rate with changes in frequency....My scan 
rate is calculated as follows.

scan rate=40Mhz/16*fin
for example for an incoming frequency of 10 khz, my scan rate would be 250
If suppose the incoming frequency is changed, I want the scan rate to be 
changed automatically so that the frequency of the look up table is updated.

 

How should this be done.........Please help