Hi, I have a very similar task to solve. I need to calculate mm per cycle.

I'm using HSC to count pulses. 1 pulse = 1mm.

HSC counts to 10 and then resets to get cm (I would count mm but reseting HSC every 1 count didn't work on great speeds).

I've set cycle interrupt to occur every 10ms and now I would like to try implement something like Pegaia explained above:

Pegaia

You can alternativaly make the follow logic in cyclic OB, for example:

atual:= ID1000:P
delta:= atual-last
if delta<0 then delta =delta + 2147483647 ' (2^31-1)
frequecy = delta/ delta time'delta time is a constant

last:= atual

But I'm concerned about negative delta.

Why adding 2147483647? For example if last value is 8 and current value is 2, delta is -6. If I add 2147483647 delta is too high.