Interrupting code

I have a have a IEtimer control on a form and 2 command buttons on a worksheet. One of the buttons enables the timer and the other button disables it.

When the timer is enabled code starts scanning cells looking for certain values and then
modifies other cells if needed. I have DoEvents in every line of code. The problem is that the second button that disables the timer, has to be pressed multiple time before it fires. Is there a way to interrupt code with one click of the button?