Hi,

You may assign pulse from wheel (or whatever) interrupt with first priority and the display multiplexing interrupt the lower priority.

Pulse interrupt to calculte RPM, high priorit for accuracy:

Display interrupt to keep displays glowing good:

At the slowest speed like @100RPM you will have the longest service time of 0.6 seconds for pulse interrupt. This will cause display to flicker.

Well you fist calculate the multiplexing rate and the display interrupt timer reload time. I think switching should be way below 0.6 seconds per display to avoid flicker.

So you may want to divide the wheel into 4, 8 or even 12 segments so as to get those many pulses per revolution. But you will have to change your formula as well to calculate the RPM from time period of 1/4, 1/8 or 1/12 revolution.

If your gadget is only one time, use extra hardware for the display for high productions do it in your code.

Regards

Babar