Hello Henk, thank you for you attention.
Yes, I clear the timer before the interrupt routine. I forget this in my example.
Pulse period I want to measure is about 512us. I have been using the crystal 11,0592MHz, so I have machine cycle period 1,085us. The result should be near 472 (+/-24 depending on input signal frequency). Timer is in 16-bit timer mode, so the result should fit into registers.
I measured the input signal by osciloscope and the period was 512us. I have no idea... Do you remember The Muppet Show? The situation is like "Pigs in space!!!" ;-))