HSC operation mode

In TIA portal the mode selection are as in the attached view.

But I cannot find in the S7-1200 system manual any reference to the mode PERIOD.

How does the counter operate in this mode ?

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In TIA portal V13 we find for the HSC properties "mode"  Counting, Period time,Frequency and Motion control.

In S7 1200 manual we cannot find any reference about period time measuring.

We use HSC to measure frequency, but for low frequency values a period measurement will be helpfull.

Best Regards,

Pier Giovanni Gordini