I am using pic 16F628A and I want it to coutdown from a max time of 99sec. It will have two 7 segment displays, but for now I am only using one so that I can experiment. The countdown sequence is set with a + 1 sec function and decreased with a -1 sec function. then I need to be able to start it with another button. I think if i can adjust the frequency a led blinks by making it go faster or slower with two different buttons then I should be able to grasp the concept.